diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..fb00b25
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,243 @@
+# This file was automatically generated by sbt-github-actions using the
+# githubWorkflowGenerate task. You should add and commit this file to
+# your git repository. It goes without saying that you shouldn't edit
+# this file by hand! Instead, if you wish to make changes, you should
+# change your sbt build configuration to revise the workflow description
+# to meet your needs, then regenerate this file.
+
+name: Continuous Integration
+
+on:
+  pull_request:
+    branches: ['**', '!update/**', '!pr/**']
+  push:
+    branches: ['**', '!update/**', '!pr/**']
+    tags: [v*]
+
+env:
+  GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+
+concurrency:
+  group: ${{ github.workflow }} @ ${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build:
+    name: Test
+    strategy:
+      matrix:
+        os: [ubuntu-22.04]
+        scala: [3]
+        java: [temurin@17]
+        project: [rootJS, rootJVM, rootNative]
+    runs-on: ${{ matrix.os }}
+    timeout-minutes: 60
+    steps:
+      - name: Checkout current branch (full)
+        uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+
+      - name: Setup sbt
+        uses: sbt/setup-sbt@v1
+
+      - name: Setup Java (temurin@17)
+        id: setup-java-temurin-17
+        if: matrix.java == 'temurin@17'
+        uses: actions/setup-java@v5
+        with:
+          distribution: temurin
+          java-version: 17
+          cache: sbt
+
+      - name: sbt update
+        if: matrix.java == 'temurin@17' && steps.setup-java-temurin-17.outputs.cache-hit == 'false'
+        run: sbt +update
+
+      - name: Check that workflows are up to date
+        run: sbt githubWorkflowCheck
+
+      - name: Check headers and formatting
+        if: matrix.java == 'temurin@17' && matrix.os == 'ubuntu-22.04'
+        run: sbt 'project ${{ matrix.project }}' '++ ${{ matrix.scala }}' headerCheckAll scalafmtCheckAll 'project /' scalafmtSbtCheck
+
+      - name: scalaJSLink
+        if: matrix.project == 'rootJS'
+        run: sbt 'project ${{ matrix.project }}' '++ ${{ matrix.scala }}' Test/scalaJSLinkerResult
+
+      - name: nativeLink
+        if: matrix.project == 'rootNative'
+        run: sbt 'project ${{ matrix.project }}' '++ ${{ matrix.scala }}' Test/nativeLink
+
+      - name: Test
+        run: sbt 'project ${{ matrix.project }}' '++ ${{ matrix.scala }}' test
+
+      - name: Check binary compatibility
+        if: matrix.java == 'temurin@17' && matrix.os == 'ubuntu-22.04'
+        run: sbt 'project ${{ matrix.project }}' '++ ${{ matrix.scala }}' mimaReportBinaryIssues
+
+      - name: Generate API documentation
+        if: matrix.java == 'temurin@17' && matrix.os == 'ubuntu-22.04'
+        run: sbt 'project ${{ matrix.project }}' '++ ${{ matrix.scala }}' doc
+
+      - name: Make target directories
+        if: github.event_name != 'pull_request' && (github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/tags/v'))
+        run: mkdir -p core/.native/target core/.js/target core/.jvm/target project/target
+
+      - name: Compress target directories
+        if: github.event_name != 'pull_request' && (github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/tags/v'))
+        run: tar cf targets.tar core/.native/target core/.js/target core/.jvm/target project/target
+
+      - name: Upload target directories
+        if: github.event_name != 'pull_request' && (github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/tags/v'))
+        uses: actions/upload-artifact@v5
+        with:
+          name: target-${{ matrix.os }}-${{ matrix.java }}-${{ matrix.scala }}-${{ matrix.project }}
+          path: targets.tar
+
+  publish:
+    name: Publish Artifacts
+    needs: [build]
+    if: github.event_name != 'pull_request' && (github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/tags/v'))
+    strategy:
+      matrix:
+        os: [ubuntu-22.04]
+        java: [temurin@17]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: Checkout current branch (full)
+        uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+
+      - name: Setup sbt
+        uses: sbt/setup-sbt@v1
+
+      - name: Setup Java (temurin@17)
+        id: setup-java-temurin-17
+        if: matrix.java == 'temurin@17'
+        uses: actions/setup-java@v5
+        with:
+          distribution: temurin
+          java-version: 17
+          cache: sbt
+
+      - name: sbt update
+        if: matrix.java == 'temurin@17' && steps.setup-java-temurin-17.outputs.cache-hit == 'false'
+        run: sbt +update
+
+      - name: Download target directories (3, rootJS)
+        uses: actions/download-artifact@v6
+        with:
+          name: target-${{ matrix.os }}-${{ matrix.java }}-3-rootJS
+
+      - name: Inflate target directories (3, rootJS)
+        run: |
+          tar xf targets.tar
+          rm targets.tar
+
+      - name: Download target directories (3, rootJVM)
+        uses: actions/download-artifact@v6
+        with:
+          name: target-${{ matrix.os }}-${{ matrix.java }}-3-rootJVM
+
+      - name: Inflate target directories (3, rootJVM)
+        run: |
+          tar xf targets.tar
+          rm targets.tar
+
+      - name: Download target directories (3, rootNative)
+        uses: actions/download-artifact@v6
+        with:
+          name: target-${{ matrix.os }}-${{ matrix.java }}-3-rootNative
+
+      - name: Inflate target directories (3, rootNative)
+        run: |
+          tar xf targets.tar
+          rm targets.tar
+
+      - name: Import signing key
+        if: env.PGP_SECRET != '' && env.PGP_PASSPHRASE == ''
+        env:
+          PGP_SECRET: ${{ secrets.PGP_SECRET }}
+          PGP_PASSPHRASE: ${{ secrets.PGP_PASSPHRASE }}
+        run: echo $PGP_SECRET | base64 -d -i - | gpg --import
+
+      - name: Import signing key and strip passphrase
+        if: env.PGP_SECRET != '' && env.PGP_PASSPHRASE != ''
+        env:
+          PGP_SECRET: ${{ secrets.PGP_SECRET }}
+          PGP_PASSPHRASE: ${{ secrets.PGP_PASSPHRASE }}
+        run: |
+          echo "$PGP_SECRET" | base64 -d -i - > /tmp/signing-key.gpg
+          echo "$PGP_PASSPHRASE" | gpg --pinentry-mode loopback --passphrase-fd 0 --import /tmp/signing-key.gpg
+          (echo "$PGP_PASSPHRASE"; echo; echo) | gpg --command-fd 0 --pinentry-mode loopback --change-passphrase $(gpg --list-secret-keys --with-colons 2> /dev/null | grep '^sec:' | cut --delimiter ':' --fields 5 | tail -n 1)
+
+      - name: Publish
+        env:
+          SONATYPE_USERNAME: ${{ secrets.SONATYPE_USERNAME }}
+          SONATYPE_PASSWORD: ${{ secrets.SONATYPE_PASSWORD }}
+          SONATYPE_CREDENTIAL_HOST: ${{ secrets.SONATYPE_CREDENTIAL_HOST }}
+        run: sbt tlCiRelease
+
+  dependency-submission:
+    name: Submit Dependencies
+    if: github.event.repository.fork == false && github.event_name != 'pull_request'
+    strategy:
+      matrix:
+        os: [ubuntu-22.04]
+        java: [temurin@17]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: Checkout current branch (full)
+        uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+
+      - name: Setup sbt
+        uses: sbt/setup-sbt@v1
+
+      - name: Setup Java (temurin@17)
+        id: setup-java-temurin-17
+        if: matrix.java == 'temurin@17'
+        uses: actions/setup-java@v5
+        with:
+          distribution: temurin
+          java-version: 17
+          cache: sbt
+
+      - name: sbt update
+        if: matrix.java == 'temurin@17' && steps.setup-java-temurin-17.outputs.cache-hit == 'false'
+        run: sbt +update
+
+      - name: Submit Dependencies
+        uses: scalacenter/sbt-dependency-submission@v2
+        with:
+          modules-ignore: rootjs_3 rootjvm_3 rootnative_3
+          configs-ignore: test scala-tool scala-doc-tool test-internal
+
+  validate-steward:
+    name: Validate Steward Config
+    strategy:
+      matrix:
+        os: [ubuntu-22.04]
+        java: [temurin@17]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: Checkout current branch (fast)
+        uses: actions/checkout@v6
+
+      - name: Setup Java (temurin@17)
+        id: setup-java-temurin-17
+        if: matrix.java == 'temurin@17'
+        uses: actions/setup-java@v5
+        with:
+          distribution: temurin
+          java-version: 17
+
+      - uses: coursier/setup-action@v1
+        with:
+          apps: scala-steward
+
+      - run: scala-steward validate-repo-config .scala-steward.conf
diff --git a/.github/workflows/clean.yml b/.github/workflows/clean.yml
new file mode 100644
index 0000000..547aaa4
--- /dev/null
+++ b/.github/workflows/clean.yml
@@ -0,0 +1,59 @@
+# This file was automatically generated by sbt-github-actions using the
+# githubWorkflowGenerate task. You should add and commit this file to
+# your git repository. It goes without saying that you shouldn't edit
+# this file by hand! Instead, if you wish to make changes, you should
+# change your sbt build configuration to revise the workflow description
+# to meet your needs, then regenerate this file.
+
+name: Clean
+
+on: push
+
+jobs:
+  delete-artifacts:
+    name: Delete Artifacts
+    runs-on: ubuntu-latest
+    env:
+      GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+    steps:
+      - name: Delete artifacts
+        run: |
+          # Customize those three lines with your repository and credentials:
+          REPO=${GITHUB_API_URL}/repos/${{ github.repository }}
+
+          # A shortcut to call GitHub API.
+          ghapi() { curl --silent --location --user _:$GITHUB_TOKEN "$@"; }
+
+          # A temporary file which receives HTTP response headers.
+          TMPFILE=/tmp/tmp.$$
+
+          # An associative array, key: artifact name, value: number of artifacts of that name.
+          declare -A ARTCOUNT
+
+          # Process all artifacts on this repository, loop on returned "pages".
+          URL=$REPO/actions/artifacts
+          while [[ -n "$URL" ]]; do
+
+            # Get current page, get response headers in a temporary file.
+            JSON=$(ghapi --dump-header $TMPFILE "$URL")
+
+            # Get URL of next page. Will be empty if we are at the last page.
+            URL=$(grep '^Link:' "$TMPFILE" | tr ',' '\n' | grep 'rel="next"' | head -1 | sed -e 's/.*<//' -e 's/>.*//')
+            rm -f $TMPFILE
+
+            # Number of artifacts on this page:
+            COUNT=$(( $(jq <<<$JSON -r '.artifacts | length') ))
+
+            # Loop on all artifacts on this page.
+            for ((i=0; $i < $COUNT; i++)); do
+
+              # Get name of artifact and count instances of this name.
+              name=$(jq <<<$JSON -r ".artifacts[$i].name?")
+              ARTCOUNT[$name]=$(( $(( ${ARTCOUNT[$name]} )) + 1))
+
+              id=$(jq <<<$JSON -r ".artifacts[$i].id?")
+              size=$(( $(jq <<<$JSON -r ".artifacts[$i].size_in_bytes?") ))
+              printf "Deleting '%s' #%d, %'d bytes\n" $name ${ARTCOUNT[$name]} $size
+              ghapi -X DELETE $REPO/actions/artifacts/$id
+            done
+          done
diff --git a/.gitignore b/.gitignore
index eefaae8..fea82ec 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,8 @@
+.direnv/
 .scala-build/
+**/target
 .bsp/
+node_modules/
 .metals/
+.bloop/
+metals.sbt
diff --git a/.mergify.yml b/.mergify.yml
new file mode 100644
index 0000000..883e699
--- /dev/null
+++ b/.mergify.yml
@@ -0,0 +1,27 @@
+# This file was automatically generated by sbt-typelevel-mergify using the
+# mergifyGenerate task. You should add and commit this file to
+# your git repository. It goes without saying that you shouldn't edit
+# this file by hand! Instead, if you wish to make changes, you should
+# change your sbt build configuration to revise the mergify configuration
+# to meet your needs, then regenerate this file.
+
+pull_request_rules:
+- name: merge scala-steward's PRs
+  conditions:
+  - author=scala-steward
+  - or:
+    - body~=labels:.*early-semver-patch
+    - body~=labels:.*early-semver-minor
+  - status-success=Test (ubuntu-22.04, 3, temurin@17, rootJS)
+  - status-success=Test (ubuntu-22.04, 3, temurin@17, rootJVM)
+  - status-success=Test (ubuntu-22.04, 3, temurin@17, rootNative)
+  actions:
+    merge: {}
+- name: Label core PRs
+  conditions:
+  - files~=^core/
+  actions:
+    label:
+      add:
+      - core
+      remove: []
diff --git a/.scala-steward.conf b/.scala-steward.conf
new file mode 100644
index 0000000..3e2ad3a
--- /dev/null
+++ b/.scala-steward.conf
@@ -0,0 +1,3 @@
+updates.cooldown = {
+  minimumAge = "7 days"
+}
diff --git a/.scalafmt.conf b/.scalafmt.conf
new file mode 100644
index 0000000..23dbe0f
--- /dev/null
+++ b/.scalafmt.conf
@@ -0,0 +1,36 @@
+version = 3.11.1
+runner.dialect=scala3
+
+runner.dialectOverride.allowSignificantIndentation = false
+runner.dialectOverride.allowQuietSyntax = true
+
+maxColumn = 100
+align.preset = some
+
+newlines.beforeMultiline = unfold
+newlines.topLevelStatements = [before, after]
+newlines.topLevelStatementsMinBreaks = 2
+newlines.implicitParamListModifierForce = [before]
+continuationIndent.defnSite = 2
+continuationIndent.extendSite = 2
+optIn.breakChainOnFirstMethodDot = true
+includeCurlyBraceInSelectChains = true
+includeNoParensInSelectChains = true
+
+trailingCommas = "multiple"
+
+rewrite.rules = [
+  RedundantBraces,
+  RedundantParens,
+  ExpandImportSelectors,
+  PreferCurlyFors
+]
+
+runner.optimizer.forceConfigStyleMinArgCount = 3
+danglingParentheses.defnSite = true
+danglingParentheses.callSite = true
+danglingParentheses.exclude = [
+  "`trait`"
+]
+verticalMultiline.newlineAfterOpenParen = true
+verticalMultiline.atDefnSite = true
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..4bf9933
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,13 @@
+   Copyright 2026 Polyvariant
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
diff --git a/build.sbt b/build.sbt
new file mode 100644
index 0000000..684ce85
--- /dev/null
+++ b/build.sbt
@@ -0,0 +1,50 @@
+ThisBuild / tlBaseVersion := "0.1"
+ThisBuild / organization := "org.polyvariant"
+ThisBuild / organizationName := "Polyvariant"
+ThisBuild / startYear := Some(2026)
+ThisBuild / licenses := Seq(License.Apache2)
+ThisBuild / developers := List(tlGitHubDev("kubukoz", "Jakub Kozłowski"))
+
+ThisBuild / githubWorkflowPublishTargetBranches := Seq(
+  RefPredicate.Equals(Ref.Branch("main")),
+  RefPredicate.StartsWith(Ref.Tag("v")),
+)
+
+ThisBuild / scalaVersion := "3.9.0"
+ThisBuild / tlJdkRelease := Some(17)
+ThisBuild / githubWorkflowJavaVersions := Seq(JavaSpec.temurin("17"))
+ThisBuild / tlFatalWarnings := false
+
+ThisBuild / mergifyStewardConfig ~= (_.map(_.withMergeMinors(true)))
+
+val hearthVersion = "0.4.2"
+val kindlingsVersion = "0.3.2"
+val http4sVersion = "0.23.37"
+val circeVersion = "0.14.16"
+
+lazy val core = crossProject(JVMPlatform, JSPlatform, NativePlatform)
+  .crossType(CrossType.Pure)
+  .in(file("core"))
+  .settings(
+    name := "jev4s",
+    scalacOptions ++= Seq(
+      "-no-indent",
+      "-Wunused:all",
+    ),
+    addCompilerPlugin("com.kubuszok" %% "hearth-cross-quotes" % hearthVersion),
+    libraryDependencies ++= Seq(
+      "org.typelevel" %%% "cats-effect" % "3.7.1",
+      "org.typelevel" %%% "cats-free" % "2.13.0",
+      "org.http4s" %%% "http4s-client" % http4sVersion,
+      "org.http4s" %%% "http4s-circe" % http4sVersion,
+      "io.circe" %%% "circe-core" % circeVersion,
+      "com.kubuszok" %%% "hearth" % hearthVersion,
+      "com.kubuszok" %%% "kindlings-derivation-commons" % kindlingsVersion,
+      "com.kubuszok" %%% "kindlings-circe-derivation" % kindlingsVersion,
+      "org.typelevel" %%% "munit-cats-effect" % "2.2.1" % Test,
+      "org.http4s" %%% "http4s-ember-client" % http4sVersion % Test,
+      "io.circe" %%% "circe-parser" % circeVersion % Test,
+    ),
+  )
+
+lazy val root = tlCrossRootProject.aggregate(core)
diff --git a/src/jev4s/Jev.scala b/core/src/main/scala/jev4s/Jev.scala
similarity index 64%
rename from src/jev4s/Jev.scala
rename to core/src/main/scala/jev4s/Jev.scala
index 3844524..efec0ec 100644
--- a/src/jev4s/Jev.scala
+++ b/core/src/main/scala/jev4s/Jev.scala
@@ -1,3 +1,19 @@
+/*
+ * Copyright 2026 Polyvariant
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 package jev4s
 
 import cats.effect.Concurrent
@@ -30,8 +46,9 @@ import scala.concurrent.duration.*
 /** A client for TypeSafe's System One models (Jev). */
 trait Jev[F[_]] {
 
-  /** Evaluates every question in `question` against `state` in one request. `state` is any JSON-encodable value:
-    * a String for plain text, or a case class / map / list for structured context.
+  /** Evaluates every question in `question` against `state` in one request. `state` is any
+    * JSON-encodable value: a String for plain text, or a case class / map / list for structured
+    * context.
     */
   def evaluate[S: Encoder, A](state: S, question: Question[A]): F[Evaluation[A]]
 
@@ -57,7 +74,9 @@ object JevConfig {
     val disabled: RetryConfig = RetryConfig(maxRetries = 0, maxBackoff = Duration.Zero)
   }
 
-  /** Reads `TYPESAFE_API_KEY` (required), `TYPESAFE_BASE_URL` and `TYPESAFE_DEFAULT_MODEL`, like the official SDKs. */
+  /** Reads `TYPESAFE_API_KEY` (required), `TYPESAFE_BASE_URL` and `TYPESAFE_DEFAULT_MODEL`, like
+    * the official SDKs.
+    */
   def fromEnv[F[_]: Env: Concurrent]: F[JevConfig] =
     (
       Env[F].get("TYPESAFE_API_KEY").flatMap(_.liftTo[F](JevError.MissingApiKey)),
@@ -70,6 +89,7 @@ object JevConfig {
         model = model.fold(base.model)(ModelId(_)),
       )
     }
+
 }
 
 enum JevError(message: String) extends Exception(message) {
@@ -79,25 +99,37 @@ enum JevError(message: String) extends Exception(message) {
   case Unprocessable(body: Json) extends JevError(s"Request failed validation: ${body.noSpaces}")
   case RateLimited(body: String) extends JevError(s"Rate limited: $body")
   case Overloaded(body: String) extends JevError(s"Overloaded: $body")
-  case UnexpectedStatus(status: Status, body: String) extends JevError(s"Unexpected status $status: $body")
+  case UnexpectedStatus(status: Status, body: String)
+    extends JevError(s"Unexpected status $status: $body")
   case UnexpectedAnswer(reason: String) extends JevError(s"Unexpected answer: $reason")
 }
 
 object Jev {
 
-  /** Timeouts, connection pooling etc. are up to the `Client` you provide; retries are added on top of it. */
-  def instance[F[_]: Temporal](config: JevConfig)(using client: Client[F]): Jev[F] =
+  /** Timeouts, connection pooling etc. are up to the `Client` you provide; retries are added on top
+    * of it.
+    */
+  def instance[F[_]: Temporal](
+    config: JevConfig
+  )(
+    using client: Client[F]
+  ): Jev[F] =
     JevImpl(config, withRetries(config.retry, client))
 
   // Same statuses as the official SDKs: 408, 429, 5xx (529 included). Retry-After is honored by the middleware.
-  private def withRetries[F[_]: Temporal](config: JevConfig.RetryConfig, client: Client[F]): Client[F] =
-    if (config.maxRetries <= 0) client
+  private def withRetries[F[_]: Temporal](config: JevConfig.RetryConfig, client: Client[F])
+    : Client[F] =
+    if (config.maxRetries <= 0)
+      client
     else
       Retry[F](
         RetryPolicy(
           RetryPolicy.exponentialBackoff(config.maxBackoff, config.maxRetries),
           (_, result) =>
-            result.fold(_ => true, r => r.status.code == 408 || r.status.code == 429 || r.status.code >= 500),
+            result.fold(
+              _ => true,
+              r => r.status.code == 408 || r.status.code == 429 || r.status.code >= 500,
+            ),
         ),
         Headers.SensitiveHeaders.contains,
       )(client)
@@ -107,9 +139,17 @@ object Jev {
 
     def evaluate[S: Encoder, A](state: S, question: Question[A]): F[Evaluation[A]] =
       for {
-        body <- Question.requestBody(state, question, config.model).leftMap(JevError.InvalidQuestion(_)).liftTo[F]
-        response <- client.run(authorized(Method.POST, "v1/systemone").withEntity(body)).use(decodeOrFail[ResponseBody])
-        evaluation <- Question.decodeResponse(question, response).leftMap(JevError.UnexpectedAnswer(_)).liftTo[F]
+        body <- Question
+          .requestBody(state, question, config.model)
+          .leftMap(JevError.InvalidQuestion(_))
+          .liftTo[F]
+        response <- client
+          .run(authorized(Method.POST, "v1/systemone").withEntity(body))
+          .use(decodeOrFail[ResponseBody])
+        evaluation <- Question
+          .decodeResponse(question, response)
+          .leftMap(JevError.UnexpectedAnswer(_))
+          .liftTo[F]
       } yield evaluation
 
     def models: F[List[ModelCard]] =
@@ -127,13 +167,17 @@ object Jev {
     private def decodeOrFail[A: Decoder](response: Response[F]): F[A] = {
       given EntityDecoder[F, A] = jsonOf[F, A]
       response.status match {
-        case s if s.isSuccess                => response.as[A]
-        case Status.Unauthorized             => response.as[String].flatMap(JevError.Unauthorized(_).raiseError)
-        case Status.UnprocessableContent     => response.as[Json].flatMap(JevError.Unprocessable(_).raiseError)
-        case Status.TooManyRequests          => response.as[String].flatMap(JevError.RateLimited(_).raiseError)
-        case s if s.code == 529              => response.as[String].flatMap(JevError.Overloaded(_).raiseError)
-        case s                               => response.as[String].flatMap(JevError.UnexpectedStatus(s, _).raiseError)
+        case s if s.isSuccess    => response.as[A]
+        case Status.Unauthorized => response.as[String].flatMap(JevError.Unauthorized(_).raiseError)
+        case Status.UnprocessableContent =>
+          response.as[Json].flatMap(JevError.Unprocessable(_).raiseError)
+        case Status.TooManyRequests =>
+          response.as[String].flatMap(JevError.RateLimited(_).raiseError)
+        case s if s.code == 529 => response.as[String].flatMap(JevError.Overloaded(_).raiseError)
+        case s => response.as[String].flatMap(JevError.UnexpectedStatus(s, _).raiseError)
       }
     }
+
   }
+
 }
diff --git a/src/jev4s/Options.scala b/core/src/main/scala/jev4s/Options.scala
similarity index 66%
rename from src/jev4s/Options.scala
rename to core/src/main/scala/jev4s/Options.scala
index e4d0558..8238632 100644
--- a/src/jev4s/Options.scala
+++ b/core/src/main/scala/jev4s/Options.scala
@@ -1,3 +1,19 @@
+/*
+ * Copyright 2026 Polyvariant
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 package jev4s
 
 import cats.data.NonEmptyVector
@@ -8,8 +24,8 @@ import jev4s.internal.OptionsMacros
 
 /** The possible answers of a Choice, or the ordered levels of a Score.
   *
-  * For a Choice, `label` is the option key sent to the model (it carries meaning, unlike question IDs). For a
-  * Score, `values` must be ordered from lowest to highest level.
+  * For a Choice, `label` is the option key sent to the model (it carries meaning, unlike question
+  * IDs). For a Score, `values` must be ordered from lowest to highest level.
   */
 trait Options[A] {
   def values: NonEmptyVector[A]
@@ -18,14 +34,22 @@ trait Options[A] {
 
   final def labelledBy(f: A => String): Options[A] = Options.instance(values, f, description)
 
-  final def describedBy[D: Encoder](f: A => D): Options[A] = Options.instance(values, label, a => Some(f(a).asJson))
+  final def describedBy[D: Encoder](f: A => D): Options[A] = Options.instance(
+    values,
+    label,
+    a => Some(f(a).asJson),
+  )
+
 }
 
 object Options {
 
-  def apply[A](using o: Options[A]): Options[A] = o
+  def apply[A](
+    using o: Options[A]
+  ): Options[A] = o
 
-  def instance[A](values: NonEmptyVector[A], label: A => String, description: A => Option[Json]): Options[A] = {
+  def instance[A](values: NonEmptyVector[A], label: A => String, description: A => Option[Json])
+    : Options[A] = {
     val (v, l, d) = (values, label, description)
     new Options[A] {
       val values: NonEmptyVector[A] = v
@@ -47,8 +71,8 @@ object Options {
 
   /** Derives options for an enum (or sealed trait) of parameterless cases, in declaration order.
     *
-    * Each case is labelled by its name unless annotated with [[label]], and described by its [[description]]
-    * annotation if present. Also usable as `derives Options`.
+    * Each case is labelled by its name unless annotated with [[label]], and described by its
+    * [[description]] annotation if present. Also usable as `derives Options`.
     */
   inline def derived[A]: Options[A] = ${ OptionsMacros.derive[A] }
 
@@ -63,6 +87,11 @@ object Options {
   /** Score levels given by position: level `i` is described by the `i`-th string. */
   def levels(first: String, second: String, rest: String*): Options[Int] = {
     val all = first +: second +: rest.toVector
-    instance(NonEmptyVector.fromVectorUnsafe(all.indices.toVector), all(_), i => Some(all(i).asJson))
+    instance(
+      NonEmptyVector.fromVectorUnsafe(all.indices.toVector),
+      all(_),
+      i => Some(all(i).asJson),
+    )
   }
+
 }
diff --git a/src/jev4s/Question.scala b/core/src/main/scala/jev4s/Question.scala
similarity index 72%
rename from src/jev4s/Question.scala
rename to core/src/main/scala/jev4s/Question.scala
index b964fad..05b6107 100644
--- a/src/jev4s/Question.scala
+++ b/core/src/main/scala/jev4s/Question.scala
@@ -1,3 +1,19 @@
+/*
+ * Copyright 2026 Polyvariant
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 package jev4s
 
 import cats.Applicative
@@ -17,7 +33,9 @@ import jev4s.internal.ResponseBody
 
 import scala.collection.immutable.ListMap
 
-/** Answer to a yes/no question. There is no separate confidence: 0.5 means "yes and no equally likely". */
+/** Answer to a yes/no question. There is no separate confidence: 0.5 means "yes and no equally
+  * likely".
+  */
 final case class Noul(yes: Probability) {
   def no: Probability = yes.complement
 }
@@ -25,11 +43,17 @@ final case class Noul(yes: Probability) {
 final case class Choice[A](choice: A, probabilities: Map[A, Probability], confidence: Confidence)
 
 /** `score` is the probability-weighted level index, and can land between levels. */
-final case class Score[A](score: Double, probabilities: Map[A, Probability], confidence: Confidence) {
+final case class Score[A](
+  score: Double,
+  probabilities: Map[A, Probability],
+  confidence: Confidence,
+) {
   def mostLikely: A = probabilities.maxBy(_._2)._1
 }
 
-/** A single question: what goes over the wire, and how to read its answer. Lifted into [[Question]]. */
+/** A single question: what goes over the wire, and how to read its answer. Lifted into
+  * [[Question]].
+  */
 private[jev4s] final case class Ask[A](
   spec: QuestionSpec,
   decode: RawAnswer => Either[String, A],
@@ -39,9 +63,9 @@ private[jev4s] final case class Ask[A](
 
 /** One or more questions about the same state, whose combined answer is an `A`.
   *
-  * Compose with `mapN`/`tupled`/`traverse`: all questions in a `Question` go out in a single request and are
-  * evaluated in parallel, independently of each other. Question IDs are assigned by the library (the model never
-  * sees them), so answers can't be looked up under the wrong key.
+  * Compose with `mapN`/`tupled`/`traverse`: all questions in a `Question` go out in a single
+  * request and are evaluated in parallel, independently of each other. Question IDs are assigned by
+  * the library (the model never sees them), so answers can't be looked up under the wrong key.
   */
 opaque type Question[A] = FreeApplicative[Ask, A]
 
@@ -50,21 +74,28 @@ object Question {
   given Applicative[Question] = summon[Applicative[FreeApplicative[Ask, *]]]
 
   def noul[I: Encoder](instructions: I): Question[Noul] =
-    single(QuestionSpec.Noul(instructions.asJson, None)) { case RawAnswer.Noul(p) => Right(Noul(p)) }
+    single(QuestionSpec.Noul(instructions.asJson, None)) { case RawAnswer.Noul(p) =>
+      Right(Noul(p))
+    }
 
   /** A Noul with descriptions of what "yes" and "no" mean. */
   def noul[I: Encoder, Y: Encoder, N: Encoder](instructions: I, yes: Y, no: N): Question[Noul] =
-    single(QuestionSpec.Noul(instructions.asJson, Some(NoulCriteria(Some(yes.asJson), Some(no.asJson))))) {
-      case RawAnswer.Noul(p) => Right(Noul(p))
-    }
+    single(
+      QuestionSpec.Noul(instructions.asJson, Some(NoulCriteria(Some(yes.asJson), Some(no.asJson))))
+    ) { case RawAnswer.Noul(p) => Right(Noul(p)) }
 
   /** Picks one of `A`'s options, e.g. the cases of an enum with a `given Options`. */
-  def choice[A](using options: Options[A]): ChoicePartiallyApplied[A] = ChoicePartiallyApplied(options)
+  def choice[A](
+    using options: Options[A]
+  ): ChoicePartiallyApplied[A] = ChoicePartiallyApplied(options)
 
   /** Rates the state on `A`'s levels, lowest first. */
-  def score[A](using levels: Options[A]): ScorePartiallyApplied[A] = ScorePartiallyApplied(levels)
+  def score[A](
+    using levels: Options[A]
+  ): ScorePartiallyApplied[A] = ScorePartiallyApplied(levels)
 
   final class ChoicePartiallyApplied[A] private[Question] (options: Options[A]) {
+
     def apply[I: Encoder](instructions: I): Question[Choice[A]] = {
       val labels = options.values.toVector.map(options.label)
       val byLabel = labels.zip(options.values.toVector).toMap
@@ -73,7 +104,8 @@ object Question {
         ListMap.from(options.values.toVector.map(a => options.label(a) -> options.description(a))),
       )
       val duplicates = labels.diff(labels.distinct).distinct
-      val problems = Option.when(duplicates.nonEmpty)(s"Duplicate Choice labels: ${duplicates.mkString(", ")}")
+      val problems =
+        Option.when(duplicates.nonEmpty)(s"Duplicate Choice labels: ${duplicates.mkString(", ")}")
       single(spec, problems.toVector) { case RawAnswer.Choice(choice, probabilities, confidence) =>
         (
           lookup(byLabel, choice),
@@ -81,9 +113,11 @@ object Question {
         ).mapN(Choice(_, _, confidence))
       }
     }
+
   }
 
   final class ScorePartiallyApplied[A] private[Question] (levels: Options[A]) {
+
     def apply[I: Encoder](instructions: I): Question[Score[A]] = {
       val byIndex = levels.values.toVector.zipWithIndex.map((a, i) => i.toString -> a).toMap
       // Score criteria are descriptions only; fall back to the label when a level has none.
@@ -92,21 +126,31 @@ object Question {
         levels.values.toVector.map(a => levels.description(a).getOrElse(levels.label(a).asJson)),
       )
       single(spec) { case RawAnswer.Score(score, probabilities, confidence) =>
-        probabilities.toList
+        probabilities
+          .toList
           .traverse((k, p) => lookup(byIndex, k).tupleRight(p))
           .map(ps => Score(score, ps.toMap, confidence))
       }
     }
+
   }
 
   private def lookup[A](m: Map[String, A], key: String): Either[String, A] =
     m.get(key).toRight(s"Unexpected option in answer: $key")
 
-  private def single[A](spec: QuestionSpec, problems: Vector[String] = Vector.empty)(
+  private def single[A](
+    spec: QuestionSpec,
+    problems: Vector[String] = Vector.empty,
+  )(
     f: PartialFunction[RawAnswer, Either[String, A]]
   ): Question[A] =
     FreeApplicative.lift(
-      Ask(spec, raw => f.applyOrElse(raw, other => Left(s"Answer type mismatch: expected $spec, got $other")), problems)
+      Ask(
+        spec,
+        raw =>
+          f.applyOrElse(raw, other => Left(s"Answer type mismatch: expected $spec, got $other")),
+        problems,
+      )
     )
 
   private def idOf(index: Int): String = s"q$index"
@@ -125,7 +169,8 @@ object Question {
       })
       .getConst
 
-  private[jev4s] def requestBody[S: Encoder, A](state: S, question: Question[A], model: ModelId): Either[String, Json] = {
+  private[jev4s] def requestBody[S: Encoder, A](state: S, question: Question[A], model: ModelId)
+    : Either[String, Json] = {
     val all = specs(question)
     val definitionProblems = problems(question)
     for {
@@ -142,11 +187,13 @@ object Question {
   // Walks the questions in the same order as `specs`, so the n-th question reads the answer under `idOf(n)`.
   private type Decoding[x] = StateT[Either[String, *], Int, x]
 
-  private[jev4s] def decodeResponse[A](question: Question[A], body: ResponseBody): Either[String, Evaluation[A]] =
+  private[jev4s] def decodeResponse[A](question: Question[A], body: ResponseBody)
+    : Either[String, Evaluation[A]] =
     question
       .foldMap(new (Ask ~> Decoding) {
         def apply[x](ask: Ask[x]): Decoding[x] = StateT { index =>
-          body.answers
+          body
+            .answers
             .get(idOf(index))
             .toRight(s"Missing answer for question ${idOf(index)}")
             .flatMap(ask.decode)
@@ -155,4 +202,5 @@ object Question {
       })
       .runA(0)
       .map(Evaluation(_, body.model, body.usage))
+
 }
diff --git a/core/src/main/scala/jev4s/annotations.scala b/core/src/main/scala/jev4s/annotations.scala
new file mode 100644
index 0000000..1d01153
--- /dev/null
+++ b/core/src/main/scala/jev4s/annotations.scala
@@ -0,0 +1,25 @@
+/*
+ * Copyright 2026 Polyvariant
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package jev4s
+
+import scala.annotation.StaticAnnotation
+
+/** Overrides the option key sent to the model for an enum case. Defaults to the case name. */
+final class label(val value: String) extends StaticAnnotation
+
+/** Describes what an enum case means: a Choice option's rubric, or a Score level's description. */
+final class description(val value: String) extends StaticAnnotation
diff --git a/core/src/main/scala/jev4s/internal/OptionsMacros.scala b/core/src/main/scala/jev4s/internal/OptionsMacros.scala
new file mode 100644
index 0000000..15bb90e
--- /dev/null
+++ b/core/src/main/scala/jev4s/internal/OptionsMacros.scala
@@ -0,0 +1,38 @@
+/*
+ * Copyright 2026 Polyvariant
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package jev4s.internal
+
+import hearth.MacroCommonsScala3
+import hearth.kindlings.derivation.compiletime.AnnotationSupport
+import jev4s.Options
+
+import scala.quoted.*
+
+final private[jev4s] class OptionsMacros(q: Quotes)
+  extends MacroCommonsScala3(
+    using q
+  ),
+    AnnotationSupport,
+    OptionsMacrosImpl
+
+private[jev4s] object OptionsMacros {
+
+  def derive[A: Type](
+    using q: Quotes
+  ): Expr[Options[A]] = new OptionsMacros(q).deriveOptions[A]
+
+}
diff --git a/src/jev4s/internal/OptionsMacrosImpl.scala b/core/src/main/scala/jev4s/internal/OptionsMacrosImpl.scala
similarity index 65%
rename from src/jev4s/internal/OptionsMacrosImpl.scala
rename to core/src/main/scala/jev4s/internal/OptionsMacrosImpl.scala
index 7c641e4..d4607c9 100644
--- a/src/jev4s/internal/OptionsMacrosImpl.scala
+++ b/core/src/main/scala/jev4s/internal/OptionsMacrosImpl.scala
@@ -1,3 +1,19 @@
+/*
+ * Copyright 2026 Polyvariant
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 package jev4s.internal
 
 import hearth.*
@@ -7,7 +23,9 @@ import jev4s.Options
 import jev4s.description
 import jev4s.label
 
-/** Derives `Options[A]` for an enum or sealed trait of singleton cases, reading `@label` and `@description`. */
+/** Derives `Options[A]` for an enum or sealed trait of singleton cases, reading `@label` and
+  * `@description`.
+  */
 private[jev4s] trait OptionsMacrosImpl { this: MacroCommons & StdExtensions & AnnotationSupport =>
 
   def deriveOptions[A: Type]: Expr[Options[A]] = {
@@ -17,7 +35,9 @@ private[jev4s] trait OptionsMacrosImpl { this: MacroCommons & StdExtensions & An
     implicit val OptionStringT: Type[Option[String]] = Type.of[Option[String]]
 
     val children = Type[A].directChildren.filter(_.nonEmpty).getOrElse {
-      Environment.reportErrorAndAbort(s"${Type[A].prettyPrint} is not an enum or sealed trait with at least one case")
+      Environment.reportErrorAndAbort(
+        s"${Type[A].prettyPrint} is not an enum or sealed trait with at least one case"
+      )
     }
 
     val cases: List[Expr[(A, String, Option[String])]] = children.toList.map { (name, child) =>
@@ -36,4 +56,5 @@ private[jev4s] trait OptionsMacrosImpl { this: MacroCommons & StdExtensions & An
 
     Expr.quote(Options.fromCases[A](Expr.splice(VarArgs.from(cases))*))
   }
+
 }
diff --git a/core/src/main/scala/jev4s/internal/wire.scala b/core/src/main/scala/jev4s/internal/wire.scala
new file mode 100644
index 0000000..49efb46
--- /dev/null
+++ b/core/src/main/scala/jev4s/internal/wire.scala
@@ -0,0 +1,117 @@
+/*
+ * Copyright 2026 Polyvariant
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package jev4s.internal
+
+import hearth.kindlings.circederivation.Configuration
+import hearth.kindlings.circederivation.KindlingsDecoder
+import hearth.kindlings.circederivation.KindlingsEncoder
+import hearth.kindlings.circederivation.annotations.fieldName
+import io.circe.Decoder
+import io.circe.Encoder
+import io.circe.Json
+import jev4s.Confidence
+import jev4s.ModelCard
+import jev4s.ModelId
+import jev4s.Probability
+import jev4s.Usage
+
+import scala.collection.immutable.ListMap
+
+/** The API's JSON conventions: snake_case fields, and a lowercase `type` discriminator on
+  * questions/answers.
+  */
+private[jev4s] val wireConfig: Configuration =
+  Configuration()
+    .withSnakeCaseMemberNames
+    .withDiscriminator("type")
+    .withTransformConstructorNames(_.toLowerCase)
+
+/** One question as it goes over the wire, minus its ID. */
+private[jev4s] enum QuestionSpec {
+  case Noul(instructions: Json, criteria: Option[NoulCriteria])
+  case Choice(instructions: Json, criteria: ListMap[String, Option[Json]])
+  case Score(instructions: Json, criteria: Vector[Json])
+
+  def validate: Either[String, Unit] =
+    this match {
+      case Noul(_, _)         => Right(())
+      case Choice(_, options) =>
+        Either.cond(
+          options.sizeIs <= 255,
+          (),
+          s"A Choice accepts at most 255 options, got ${options.size}",
+        )
+      case Score(_, levels) =>
+        Either.cond(
+          levels.sizeIs >= 2 && levels.sizeIs <= 10,
+          (),
+          s"A Score needs 2 to 10 levels, got ${levels.size}",
+        )
+    }
+
+}
+
+private[jev4s] object QuestionSpec {
+
+  given Encoder[QuestionSpec] = KindlingsEncoder.derived(
+    using wireConfig
+  )
+
+}
+
+private[jev4s] final case class NoulCriteria(
+  @fieldName("true") yes: Option[Json],
+  @fieldName("false") no: Option[Json],
+)
+
+private[jev4s] enum RawAnswer {
+  case Noul(noul: Probability)
+  case Choice(choice: String, probabilities: Map[String, Probability], confidence: Confidence)
+  case Score(score: Double, probabilities: Map[String, Probability], confidence: Confidence)
+}
+
+private[jev4s] object RawAnswer {
+
+  given Decoder[RawAnswer] = KindlingsDecoder.derived(
+    using wireConfig
+  )
+
+}
+
+private[jev4s] final case class ResponseBody(
+  model: ModelId,
+  answers: Map[String, RawAnswer],
+  usage: Usage,
+)
+
+private[jev4s] object ResponseBody {
+
+  given Decoder[ResponseBody] = KindlingsDecoder.derived(
+    using wireConfig
+  )
+
+}
+
+private[jev4s] final case class ModelList(models: List[ModelCard])
+
+private[jev4s] object ModelList {
+
+  given Decoder[ModelList] = KindlingsDecoder.derived(
+    using wireConfig
+  )
+
+}
diff --git a/src/jev4s/model.scala b/core/src/main/scala/jev4s/model.scala
similarity index 72%
rename from src/jev4s/model.scala
rename to core/src/main/scala/jev4s/model.scala
index acac128..1466b16 100644
--- a/src/jev4s/model.scala
+++ b/core/src/main/scala/jev4s/model.scala
@@ -1,3 +1,19 @@
+/*
+ * Copyright 2026 Polyvariant
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 package jev4s
 
 import cats.Order
@@ -22,7 +38,10 @@ object Probability {
     def complement: Probability = 1.0 - p
   }
 
-  given Order[Probability] = Order.fromOrdering(using Ordering.Double.TotalOrdering)
+  given Order[Probability] = Order.fromOrdering(
+    using Ordering.Double.TotalOrdering
+  )
+
   given Ordering[Probability] = Ordering.Double.TotalOrdering
   given Decoder[Probability] = Decoder.decodeDouble.map(clamped)
 }
@@ -39,7 +58,10 @@ object Confidence {
     def value: Double = c
   }
 
-  given Order[Confidence] = Order.fromOrdering(using Ordering.Double.TotalOrdering)
+  given Order[Confidence] = Order.fromOrdering(
+    using Ordering.Double.TotalOrdering
+  )
+
   given Ordering[Confidence] = Ordering.Double.TotalOrdering
   given Decoder[Confidence] = Decoder.decodeDouble.map(d => math.max(0.0, math.min(1.0, d)))
 }
@@ -67,13 +89,21 @@ object ModelId {
 final case class Usage(inputTokens: Long, outputTokens: Long)
 
 object Usage {
-  given Decoder[Usage] = KindlingsDecoder.derived(using wireConfig)
+
+  given Decoder[Usage] = KindlingsDecoder.derived(
+    using wireConfig
+  )
+
 }
 
 final case class ModelCard(name: ModelId, description: String, releaseDate: String)
 
 object ModelCard {
-  given Decoder[ModelCard] = KindlingsDecoder.derived(using wireConfig)
+
+  given Decoder[ModelCard] = KindlingsDecoder.derived(
+    using wireConfig
+  )
+
 }
 
 /** The result of one evaluation: your typed answers plus request metadata. */
diff --git a/test/example/Triage.scala b/core/src/test/scala/example/Triage.scala
similarity index 50%
rename from test/example/Triage.scala
rename to core/src/test/scala/example/Triage.scala
index f93deb1..020c262 100644
--- a/test/example/Triage.scala
+++ b/core/src/test/scala/example/Triage.scala
@@ -1,3 +1,19 @@
+/*
+ * Copyright 2026 Polyvariant
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 package example
 
 import cats.effect.IO
@@ -36,16 +52,20 @@ object Triage {
 
   val topics: List[String] = List("refund", "account access", "data loss")
 
-  val question: Question[Triage] = (
-    Question.noul(
-      "Does `message` convey urgency?",
-      yes = "Explicitly time-sensitive",
-      no = "No urgency expressed",
-    ),
-    Question.choice[Department]("Which team should handle this ticket?"),
-    Question.score[Frustration]("How frustrated is the customer?"),
-    topics.traverse(t => Question.noul(s"Does the ticket ask about $t?").tupleLeft(t)).map(_.toMap),
-  ).mapN(Triage.apply)
+  val question: Question[Triage] =
+    (
+      Question.noul(
+        "Does `message` convey urgency?",
+        yes = "Explicitly time-sensitive",
+        no = "No urgency expressed",
+      ),
+      Question.choice[Department]("Which team should handle this ticket?"),
+      Question.score[Frustration]("How frustrated is the customer?"),
+      topics
+        .traverse(t => Question.noul(s"Does the ticket ask about $t?").tupleLeft(t))
+        .map(_.toMap),
+    ).mapN(Triage.apply)
+
 }
 
 object Main extends IOApp.Simple {
@@ -61,11 +81,20 @@ object Main extends IOApp.Simple {
           Triage.question,
         )
         triage = result.answers
-        _ <- IO.println(s"answered by ${result.model.value}, ${result.usage.inputTokens} input tokens")
+        _ <- IO.println(
+          s"answered by ${result.model.value}, ${result.usage.inputTokens} input tokens"
+        )
         _ <- IO.println(s"urgent: ${triage.urgent.yes.value}")
-        _ <- IO.println(s"department: ${triage.department.choice} (confidence ${triage.department.confidence.value})")
-        _ <- IO.println(s"frustration: ${triage.frustration.score} ~ ${triage.frustration.mostLikely}")
-        _ <- IO.println(s"topics: ${triage.topics.filter(_._2.yes.value > 0.5).keys.mkString(", ")}")
+        _ <- IO.println(
+          s"department: ${triage.department.choice} (confidence ${triage.department.confidence.value})"
+        )
+        _ <- IO.println(
+          s"frustration: ${triage.frustration.score} ~ ${triage.frustration.mostLikely}"
+        )
+        _ <- IO.println(
+          s"topics: ${triage.topics.filter(_._2.yes.value > 0.5).keys.mkString(", ")}"
+        )
       } yield ()
     }
+
 }
diff --git a/test/JevTests.scala b/core/src/test/scala/jev4s/JevTests.scala
similarity index 67%
rename from test/JevTests.scala
rename to core/src/test/scala/jev4s/JevTests.scala
index dd23df8..eca5fac 100644
--- a/test/JevTests.scala
+++ b/core/src/test/scala/jev4s/JevTests.scala
@@ -1,3 +1,19 @@
+/*
+ * Copyright 2026 Polyvariant
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 package jev4s
 
 import cats.effect.IO
@@ -19,7 +35,10 @@ class JevTests extends CatsEffectSuite {
   private def fake(status: Status, body: Json): IO[(Ref[IO, List[(String, Json)]], Jev[IO])] =
     Ref[IO].of(List.empty[(String, Json)]).map { seen =>
       given Client[IO] = Client.fromHttpApp(HttpApp[IO] { req =>
-        req.as[Json].flatMap(j => seen.update(_ :+ (req.uri.renderString -> j))).as(Response[IO](status).withEntity(body))
+        req
+          .as[Json]
+          .flatMap(j => seen.update(_ :+ (req.uri.renderString -> j)))
+          .as(Response[IO](status).withEntity(body))
       })
       (seen, Jev.instance[IO](config))
     }
@@ -77,7 +96,11 @@ class JevTests extends CatsEffectSuite {
       )
       assertEquals(
         body.hcursor.downField("questions").downField("q3").focus,
-        Some(json("""{"type": "noul", "instructions": "Does the ticket ask about refund?", "criteria": null}""")),
+        Some(
+          json(
+            """{"type": "noul", "instructions": "Does the ticket ask about refund?", "criteria": null}"""
+          )
+        ),
       )
     }
   }
@@ -86,39 +109,53 @@ class JevTests extends CatsEffectSuite {
     val options = Options.derived[Plan]
     assertEquals(options.values.toVector, Vector(Plan.Free, Plan.Pro))
     assertEquals(options.values.toVector.map(options.label), Vector("Free", "paid"))
-    assertEquals(options.values.toVector.map(options.description), Vector(Some(Json.fromString("No payment")), None))
+    assertEquals(
+      options.values.toVector.map(options.description),
+      Vector(Some(Json.fromString("No payment")), None),
+    )
   }
 
   test("derivation rejects cases with fields") {
     assert(
-      compileErrors("Options.derived[WithFields]").contains("only parameterless cases can be options"),
+      compileErrors("Options.derived[WithFields]").contains(
+        "only parameterless cases can be options"
+      ),
       compileErrors("Options.derived[WithFields]"),
     )
   }
 
   test("invalid questions fail before sending") {
-    val tooFewLevels = Question.score(using Options.derived[Single])("?")
-    fake(Status.Ok, Json.obj()).flatMap((seen, jev) =>
-      jev.evaluate("x", tooFewLevels).attempt.product(seen.get)
-    ).map { (result, requests) =>
-      assert(result.left.exists(_.isInstanceOf[JevError.InvalidQuestion]), result)
-      assertEquals(requests, Nil)
-    }
+    val tooFewLevels =
+      Question.score(
+        using Options.derived[Single]
+      )("?")
+    fake(Status.Ok, Json.obj())
+      .flatMap((seen, jev) => jev.evaluate("x", tooFewLevels).attempt.product(seen.get))
+      .map { (result, requests) =>
+        assert(result.left.exists(_.isInstanceOf[JevError.InvalidQuestion]), result)
+        assertEquals(requests, Nil)
+      }
   }
 
   test("duplicate choice labels fail before sending") {
-    val question = Question.choice(using Options.labels("a", "b", "a"))("?")
-    fake(Status.Ok, Json.obj()).flatMap((seen, jev) => jev.evaluate("x", question).attempt.product(seen.get)).map {
-      (result, requests) =>
+    val question =
+      Question.choice(
+        using Options.labels("a", "b", "a")
+      )("?")
+    fake(Status.Ok, Json.obj())
+      .flatMap((seen, jev) => jev.evaluate("x", question).attempt.product(seen.get))
+      .map { (result, requests) =>
         assertEquals(result, Left(JevError.InvalidQuestion("Duplicate Choice labels: a")))
         assertEquals(requests, Nil)
-    }
+      }
   }
 
   test("422 is surfaced with its body") {
-    fake(Status.UnprocessableContent, Json.obj("detail" -> Json.fromString("bad"))).flatMap((_, jev) =>
-      jev.evaluate("x", Question.noul("?")).attempt
-    ).map(r => assertEquals(r, Left(JevError.Unprocessable(Json.obj("detail" -> Json.fromString("bad"))))))
+    fake(Status.UnprocessableContent, Json.obj("detail" -> Json.fromString("bad")))
+      .flatMap((_, jev) => jev.evaluate("x", Question.noul("?")).attempt)
+      .map(r =>
+        assertEquals(r, Left(JevError.Unprocessable(Json.obj("detail" -> Json.fromString("bad")))))
+      )
   }
 }
 
@@ -127,6 +164,7 @@ enum Single {
 }
 
 sealed trait Plan
+
 object Plan {
   @description("No payment") case object Free extends Plan
   @label("paid") case object Pro extends Plan
diff --git a/project.scala b/project.scala
deleted file mode 100644
index 7aa8db8..0000000
--- a/project.scala
+++ /dev/null
@@ -1,14 +0,0 @@
-//> using scala 3.9.0
-//> using options -deprecation -feature -Wunused:all -no-indent -Xkind-projector
-//> using dep org.typelevel::cats-effect:3.7.1
-//> using dep org.typelevel::cats-free:2.13.0
-//> using dep org.http4s::http4s-client:0.23.37
-//> using dep org.http4s::http4s-circe:0.23.37
-//> using dep io.circe::circe-core:0.14.16
-//> using dep com.kubuszok::hearth:0.4.2
-//> using dep com.kubuszok::kindlings-derivation-commons:0.3.2
-//> using dep com.kubuszok::kindlings-circe-derivation:0.3.2
-//> using plugin com.kubuszok::hearth-cross-quotes:0.4.2
-//> using test.dep org.typelevel::munit-cats-effect:2.2.1
-//> using test.dep org.http4s::http4s-ember-client:0.23.37
-//> using test.dep io.circe::circe-parser:0.14.16
diff --git a/project/build.properties b/project/build.properties
new file mode 100644
index 0000000..7c95fc1
--- /dev/null
+++ b/project/build.properties
@@ -0,0 +1 @@
+sbt.version=1.12.13
diff --git a/project/plugins.sbt b/project/plugins.sbt
new file mode 100644
index 0000000..3c54962
--- /dev/null
+++ b/project/plugins.sbt
@@ -0,0 +1,5 @@
+addSbtPlugin("org.typelevel" % "sbt-typelevel" % "0.8.7")
+addSbtPlugin("org.typelevel" % "sbt-typelevel-mergify" % "0.8.7")
+// sbt-scalajs-crossproject and sbt-scala-native-crossproject are pulled in transitively by sbt-typelevel.
+addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.22.0")
+addSbtPlugin("org.scala-native" % "sbt-scala-native" % "0.5.12")
diff --git a/src/jev4s/annotations.scala b/src/jev4s/annotations.scala
deleted file mode 100644
index 4944142..0000000
--- a/src/jev4s/annotations.scala
+++ /dev/null
@@ -1,9 +0,0 @@
-package jev4s
-
-import scala.annotation.StaticAnnotation
-
-/** Overrides the option key sent to the model for an enum case. Defaults to the case name. */
-final class label(val value: String) extends StaticAnnotation
-
-/** Describes what an enum case means: a Choice option's rubric, or a Score level's description. */
-final class description(val value: String) extends StaticAnnotation
diff --git a/src/jev4s/internal/OptionsMacros.scala b/src/jev4s/internal/OptionsMacros.scala
deleted file mode 100644
index 9889cb9..0000000
--- a/src/jev4s/internal/OptionsMacros.scala
+++ /dev/null
@@ -1,16 +0,0 @@
-package jev4s.internal
-
-import hearth.MacroCommonsScala3
-import hearth.kindlings.derivation.compiletime.AnnotationSupport
-import jev4s.Options
-
-import scala.quoted.*
-
-final private[jev4s] class OptionsMacros(q: Quotes)
-    extends MacroCommonsScala3(using q),
-      AnnotationSupport,
-      OptionsMacrosImpl
-
-private[jev4s] object OptionsMacros {
-  def derive[A: Type](using q: Quotes): Expr[Options[A]] = new OptionsMacros(q).deriveOptions[A]
-}
diff --git a/src/jev4s/internal/wire.scala b/src/jev4s/internal/wire.scala
deleted file mode 100644
index 0dcfdb3..0000000
--- a/src/jev4s/internal/wire.scala
+++ /dev/null
@@ -1,66 +0,0 @@
-package jev4s.internal
-
-import hearth.kindlings.circederivation.Configuration
-import hearth.kindlings.circederivation.KindlingsDecoder
-import hearth.kindlings.circederivation.KindlingsEncoder
-import hearth.kindlings.circederivation.annotations.fieldName
-import io.circe.Decoder
-import io.circe.Encoder
-import io.circe.Json
-import jev4s.Confidence
-import jev4s.ModelCard
-import jev4s.ModelId
-import jev4s.Probability
-import jev4s.Usage
-
-import scala.collection.immutable.ListMap
-
-/** The API's JSON conventions: snake_case fields, and a lowercase `type` discriminator on questions/answers. */
-private[jev4s] val wireConfig: Configuration =
-  Configuration()
-    .withSnakeCaseMemberNames
-    .withDiscriminator("type")
-    .withTransformConstructorNames(_.toLowerCase)
-
-/** One question as it goes over the wire, minus its ID. */
-private[jev4s] enum QuestionSpec {
-  case Noul(instructions: Json, criteria: Option[NoulCriteria])
-  case Choice(instructions: Json, criteria: ListMap[String, Option[Json]])
-  case Score(instructions: Json, criteria: Vector[Json])
-
-  def validate: Either[String, Unit] = this match {
-    case Noul(_, _) => Right(())
-    case Choice(_, options) =>
-      Either.cond(options.sizeIs <= 255, (), s"A Choice accepts at most 255 options, got ${options.size}")
-    case Score(_, levels) =>
-      Either.cond(levels.sizeIs >= 2 && levels.sizeIs <= 10, (), s"A Score needs 2 to 10 levels, got ${levels.size}")
-  }
-}
-
-private[jev4s] object QuestionSpec {
-  given Encoder[QuestionSpec] = KindlingsEncoder.derived(using wireConfig)
-}
-
-private[jev4s] final case class NoulCriteria(@fieldName("true") yes: Option[Json], @fieldName("false") no: Option[Json])
-
-private[jev4s] enum RawAnswer {
-  case Noul(noul: Probability)
-  case Choice(choice: String, probabilities: Map[String, Probability], confidence: Confidence)
-  case Score(score: Double, probabilities: Map[String, Probability], confidence: Confidence)
-}
-
-private[jev4s] object RawAnswer {
-  given Decoder[RawAnswer] = KindlingsDecoder.derived(using wireConfig)
-}
-
-private[jev4s] final case class ResponseBody(model: ModelId, answers: Map[String, RawAnswer], usage: Usage)
-
-private[jev4s] object ResponseBody {
-  given Decoder[ResponseBody] = KindlingsDecoder.derived(using wireConfig)
-}
-
-private[jev4s] final case class ModelList(models: List[ModelCard])
-
-private[jev4s] object ModelList {
-  given Decoder[ModelList] = KindlingsDecoder.derived(using wireConfig)
-}