diff --git a/.github/workflows/pull_request.yml b/.github/workflows/pull_request.yml
index 8dc98243..234bf631 100644
--- a/.github/workflows/pull_request.yml
+++ b/.github/workflows/pull_request.yml
@@ -1,4 +1,5 @@
 name: Pull Request Check
+
 on:
   pull_request:
     branches:
@@ -16,6 +17,12 @@ on:
       - gradle.properties
       - settings.gradle
 
+permissions:
+  contents: read
+  actions: read
+  packages: read
+  pull-requests: write
+
 jobs:
   codec:
     uses: ./.github/workflows/build_and_test.yml
@@ -184,3 +191,227 @@ jobs:
       ci_build: true
       pr_build: true
       gametest: true
+
+  # ── Roseau API checks ──────────────────────────────────────────
+
+  codec-roseau:
+    needs: codec
+    uses: ./.github/workflows/roseau_check.yml
+    with:
+      module: codec
+      module_id: anvillib-codec
+
+  collision-roseau:
+    needs: collision
+    uses: ./.github/workflows/roseau_check.yml
+    with:
+      module: collision
+      module_id: anvillib-collision
+
+  config-roseau:
+    needs: config
+    uses: ./.github/workflows/roseau_check.yml
+    with:
+      module: config
+      module_id: anvillib-config
+
+  font-roseau:
+    needs: font
+    uses: ./.github/workflows/roseau_check.yml
+    with:
+      module: font
+      module_id: anvillib-font
+
+  integration-roseau:
+    needs: integration
+    uses: ./.github/workflows/roseau_check.yml
+    with:
+      module: integration
+      module_id: anvillib-integration
+
+  moveable-entity-block-roseau:
+    needs: moveable-entity-block
+    uses: ./.github/workflows/roseau_check.yml
+    with:
+      module: moveable-entity-block
+      module_id: anvillib-moveable-entity-block
+
+  multiblock-roseau:
+    needs: multiblock
+    uses: ./.github/workflows/roseau_check.yml
+    with:
+      module: multiblock
+      module_id: anvillib-multiblock
+
+  network-roseau:
+    needs: network
+    uses: ./.github/workflows/roseau_check.yml
+    with:
+      module: network
+      module_id: anvillib-network
+
+  recipe-roseau:
+    needs: recipe
+    uses: ./.github/workflows/roseau_check.yml
+    with:
+      module: recipe
+      module_id: anvillib-recipe
+
+  registrum-roseau:
+    needs: registrum
+    uses: ./.github/workflows/roseau_check.yml
+    with:
+      module: registrum
+      module_id: anvillib-registrum
+
+  rendering-roseau:
+    needs: rendering
+    uses: ./.github/workflows/roseau_check.yml
+    with:
+      module: rendering
+      module_id: anvillib-rendering
+
+  space-select-roseau:
+    needs: space-select
+    uses: ./.github/workflows/roseau_check.yml
+    with:
+      module: space-select
+      module_id: anvillib-space-select
+
+  sync-roseau:
+    needs: sync
+    uses: ./.github/workflows/roseau_check.yml
+    with:
+      module: sync
+      module_id: anvillib-sync
+
+  util-roseau:
+    needs: util
+    uses: ./.github/workflows/roseau_check.yml
+    with:
+      module: util
+      module_id: anvillib-util
+
+  wheel-roseau:
+    needs: wheel
+    uses: ./.github/workflows/roseau_check.yml
+    with:
+      module: wheel
+      module_id: anvillib-wheel
+
+  main-roseau:
+    needs: main
+    uses: ./.github/workflows/roseau_check.yml
+    with:
+      module: main
+      module_id: anvillib
+
+  # ── Roseau summary comment ─────────────────────────────────────
+
+  roseau-summary:
+    needs:
+      - codec-roseau
+      - collision-roseau
+      - config-roseau
+      - font-roseau
+      - integration-roseau
+      - moveable-entity-block-roseau
+      - multiblock-roseau
+      - network-roseau
+      - recipe-roseau
+      - registrum-roseau
+      - rendering-roseau
+      - space-select-roseau
+      - sync-roseau
+      - util-roseau
+      - wheel-roseau
+      - main-roseau
+    if: always()
+    runs-on: ubuntu-latest
+    env:
+      CODEC_BC: ${{ needs.codec-roseau.outputs.has_bc }}
+      CODEC_N: ${{ needs.codec-roseau.outputs.bc_count }}
+      COLLISION_BC: ${{ needs.collision-roseau.outputs.has_bc }}
+      COLLISION_N: ${{ needs.collision-roseau.outputs.bc_count }}
+      CONFIG_BC: ${{ needs.config-roseau.outputs.has_bc }}
+      CONFIG_N: ${{ needs.config-roseau.outputs.bc_count }}
+      FONT_BC: ${{ needs.font-roseau.outputs.has_bc }}
+      FONT_N: ${{ needs.font-roseau.outputs.bc_count }}
+      INTEGRATION_BC: ${{ needs.integration-roseau.outputs.has_bc }}
+      INTEGRATION_N: ${{ needs.integration-roseau.outputs.bc_count }}
+      MEB_BC: ${{ needs.moveable-entity-block-roseau.outputs.has_bc }}
+      MEB_N: ${{ needs.moveable-entity-block-roseau.outputs.bc_count }}
+      MULTIBLOCK_BC: ${{ needs.multiblock-roseau.outputs.has_bc }}
+      MULTIBLOCK_N: ${{ needs.multiblock-roseau.outputs.bc_count }}
+      NETWORK_BC: ${{ needs.network-roseau.outputs.has_bc }}
+      NETWORK_N: ${{ needs.network-roseau.outputs.bc_count }}
+      RECIPE_BC: ${{ needs.recipe-roseau.outputs.has_bc }}
+      RECIPE_N: ${{ needs.recipe-roseau.outputs.bc_count }}
+      REGISTRUM_BC: ${{ needs.registrum-roseau.outputs.has_bc }}
+      REGISTRUM_N: ${{ needs.registrum-roseau.outputs.bc_count }}
+      RENDERING_BC: ${{ needs.rendering-roseau.outputs.has_bc }}
+      RENDERING_N: ${{ needs.rendering-roseau.outputs.bc_count }}
+      SPACESELECT_BC: ${{ needs.space-select-roseau.outputs.has_bc }}
+      SPACESELECT_N: ${{ needs.space-select-roseau.outputs.bc_count }}
+      SYNC_BC: ${{ needs.sync-roseau.outputs.has_bc }}
+      SYNC_N: ${{ needs.sync-roseau.outputs.bc_count }}
+      UTIL_BC: ${{ needs.util-roseau.outputs.has_bc }}
+      UTIL_N: ${{ needs.util-roseau.outputs.bc_count }}
+      WHEEL_BC: ${{ needs.wheel-roseau.outputs.has_bc }}
+      WHEEL_N: ${{ needs.wheel-roseau.outputs.bc_count }}
+      MAIN_BC: ${{ needs.main-roseau.outputs.has_bc }}
+      MAIN_N: ${{ needs.main-roseau.outputs.bc_count }}
+    steps:
+      - name: Generate and post PR comment
+        run: |
+          row() {
+            local name=$1 bc=$2 count=$3
+            if [ -z "$bc" ]; then
+              echo "| ${name} | ⚪ Skipped | — |"
+            elif [ "$bc" = "true" ]; then
+              echo "| ${name} | 🔴 BC detected | ${count} |"
+            else
+              echo "| ${name} | ✅ Compatible | 0 |"
+            fi
+          }
+
+          {
+            echo "## 🌿 Roseau API Breaking Change Report"
+            echo ""
+            echo "| Module | Status | Breaking Changes |"
+            echo "|--------|--------|-----------------|"
+            row "codec"                 "$CODEC_BC"       "$CODEC_N"
+            row "collision"             "$COLLISION_BC"   "$COLLISION_N"
+            row "config"                "$CONFIG_BC"      "$CONFIG_N"
+            row "font"                  "$FONT_BC"        "$FONT_N"
+            row "integration"           "$INTEGRATION_BC" "$INTEGRATION_N"
+            row "moveable-entity-block" "$MEB_BC"         "$MEB_N"
+            row "multiblock"            "$MULTIBLOCK_BC"  "$MULTIBLOCK_N"
+            row "network"               "$NETWORK_BC"     "$NETWORK_N"
+            row "recipe"                "$RECIPE_BC"      "$RECIPE_N"
+            row "registrum"             "$REGISTRUM_BC"   "$REGISTRUM_N"
+            row "rendering"             "$RENDERING_BC"   "$RENDERING_N"
+            row "space-select"          "$SPACESELECT_BC" "$SPACESELECT_N"
+            row "sync"                  "$SYNC_BC"        "$SYNC_N"
+            row "util"                  "$UTIL_BC"        "$UTIL_N"
+            row "wheel"                 "$WHEEL_BC"       "$WHEEL_N"
+            row "main"                  "$MAIN_BC"        "$MAIN_N"
+            echo ""
+            echo "> Detailed reports: see the *Artifacts* section of [this workflow run](${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }})."
+          } > /tmp/roseau-body.md
+
+      - name: Find existing Roseau comment
+        id: find-comment
+        uses: peter-evans/find-comment@v3
+        with:
+          issue-number: ${{ github.event.pull_request.number }}
+          comment-author: github-actions[bot]
+          body-includes: Roseau API Breaking Change Report
+
+      - name: Create or update PR comment
+        uses: peter-evans/create-or-update-comment@v4
+        with:
+          comment-id: ${{ steps.find-comment.outputs.comment-id }}
+          issue-number: ${{ github.event.pull_request.number }}
+          body-path: /tmp/roseau-body.md
+          edit-mode: replace
diff --git a/.github/workflows/roseau_check.yml b/.github/workflows/roseau_check.yml
new file mode 100644
index 00000000..a3a3d052
--- /dev/null
+++ b/.github/workflows/roseau_check.yml
@@ -0,0 +1,75 @@
+name: Roseau Check
+
+on:
+  workflow_call:
+    inputs:
+      module:
+        description: 'Module directory name (e.g. codec, config)'
+        required: true
+        type: string
+      module_id:
+        description: 'Module short ID (e.g. anvillib-codec)'
+        required: true
+        type: string
+    outputs:
+      has_bc:
+        description: 'Whether breaking changes were detected'
+        value: ${{ jobs.check.outputs.has_bc }}
+      bc_count:
+        description: 'Number of breaking changes'
+        value: ${{ jobs.check.outputs.bc_count }}
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    outputs:
+      has_bc: ${{ steps.result.outputs.has_bc }}
+      bc_count: ${{ steps.result.outputs.bc_count }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - name: Read Java version
+        id: properties
+        uses: christian-draeger/read-properties@1.1.1
+        with:
+          path: gradle.properties
+          properties: java_version
+
+      - name: Setup Java ${{ steps.properties.outputs.java_version }}
+        uses: actions/setup-java@v5.2.0
+        with:
+          distribution: zulu
+          java-version: ${{ steps.properties.outputs.java_version }}
+
+      - name: Setup Gradle
+        uses: gradle/actions/setup-gradle@v6
+
+      - name: Run roseauCheck
+        id: roseau
+        continue-on-error: true
+        run: ./gradlew :${{ inputs.module_id }}-neoforge-26.1:roseauCheck
+
+      - name: Collect result
+        id: result
+        if: always()
+        run: |
+          CSV="module.${{ inputs.module }}/build/reports/roseau/report.csv"
+          if [ -f "$CSV" ] && [ "$(wc -l < "$CSV")" -gt 1 ]; then
+            COUNT=$(($(wc -l < "$CSV") - 1))
+            echo "has_bc=true" >> $GITHUB_OUTPUT
+            echo "bc_count=${COUNT}" >> $GITHUB_OUTPUT
+            echo "Roseau: ${COUNT} breaking change(s) in ${{ inputs.module }}"
+          else
+            echo "has_bc=false" >> $GITHUB_OUTPUT
+            echo "bc_count=0" >> $GITHUB_OUTPUT
+            echo "Roseau: no breaking changes in ${{ inputs.module }}"
+          fi
+
+      - name: Upload report
+        if: always()
+        uses: actions/upload-artifact@v7
+        with:
+          name: roseau-${{ inputs.module }}
+          path: module.${{ inputs.module }}/build/reports/roseau/
+          retention-days: 7
diff --git a/build.gradle b/build.gradle
index b56cc632..17481b2e 100644
--- a/build.gradle
+++ b/build.gradle
@@ -124,4 +124,7 @@ subprojects {
     apply plugin: "me.modmuss50.mod-publish-plugin"
 
     apply from: rootProject.file("module.gradle")
+    if (it.name != "anvillib-test-neoforge-26.1") {
+        apply from: rootProject.file("gradle/scripts/roseau.gradle")
+    }
 }
diff --git a/gradle/scripts/roseau.gradle b/gradle/scripts/roseau.gradle
new file mode 100644
index 00000000..ec0ca4e6
--- /dev/null
+++ b/gradle/scripts/roseau.gradle
@@ -0,0 +1,76 @@
+configurations {
+    roseau
+}
+
+dependencies {
+    roseau 'io.github.alien-tools:roseau-cli:0.6.0'
+}
+
+def jarFileProvider = tasks.named('jar').flatMap { it.archiveFile }
+def reportsDirProvider = layout.buildDirectory.dir('reports/roseau')
+def compileClasspathProvider = provider { sourceSets.main.compileClasspath.asPath }
+def roseauGroup = project.group.toString()
+def roseauArtifact = project.name
+def roseauBaselineVersion = project.findProperty('roseauBaselineVersion') ?: {
+    def groupPath = project.group.toString().replace('.', '/')
+    def artifact = project.name
+    def repos = [
+            'https://repo1.maven.org/maven2',
+            'https://server.cjsah.net:1002/maven',
+    ]
+    for (repoUrl in repos) {
+        try {
+            def metadataUrl = new URL("${repoUrl}/${groupPath}/${artifact}/maven-metadata.xml")
+            def conn = metadataUrl.openConnection()
+            conn.connectTimeout = 5000
+            conn.readTimeout = 5000
+            def xmlText = conn.inputStream.getText('UTF-8')
+            def matcher = xmlText =~ /<latest>([^<]+)<\/latest>/
+            if (matcher.find()) {
+                def latest = matcher.group(1)
+                logger.lifecycle("Roseau: resolved latest version ${latest} from ${repoUrl}")
+                return latest
+            }
+        } catch (Exception ignored) {
+            // try next repo
+        }
+    }
+    logger.warn("Roseau: could not resolve latest version from Maven, falling back to ${version}")
+    return version.toString()
+}()
+def roseauMvnCoord = "${roseauGroup}:${roseauArtifact}:${roseauBaselineVersion}"
+def roseauBaselineDep = dependencies.create(group: roseauGroup, name: roseauArtifact, version: roseauBaselineVersion)
+def roseauBaselineConfig = configurations.detachedConfiguration(roseauBaselineDep)
+def roseauBaselineJarProvider = provider { roseauBaselineConfig.singleFile }
+
+tasks.register('roseauCheck', JavaExec) {
+    group = 'verification'
+    description = 'Detects API breaking changes against a baseline version using Roseau'
+
+    dependsOn tasks.named('jar')
+
+    classpath = configurations.roseau
+    mainClass = 'io.github.alien.roseau.cli.RoseauCLI'
+    javaLauncher = javaToolchains.launcherFor {
+        languageVersion = JavaLanguageVersion.of(Integer.parseInt(project.java_version))
+    }
+
+    doFirst {
+        def currentJar = jarFileProvider.get().asFile
+        def baselineJar = roseauBaselineJarProvider.get()
+        def reportsDir = reportsDirProvider.get().asFile
+        reportsDir.mkdirs()
+
+        logger.lifecycle("Roseau: comparing baseline ${roseauMvnCoord} against ${currentJar.name}")
+
+        args(
+                '--diff',
+                '--v1', baselineJar.absolutePath,
+                '--v2', currentJar.absolutePath,
+                '--classpath', compileClasspathProvider.get(),
+                '--fail-on-bc',
+                '--report', "HTML=${new File(reportsDir, 'report.html').absolutePath}",
+                '--report', "CSV=${new File(reportsDir, 'report.csv').absolutePath}",
+        )
+    }
+}