diff --git a/.gitignore b/.gitignore
index f01ed3a0a..414c524a1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -10,6 +10,9 @@ genesis.json
 /op-reth
 .env
 
+# decker (local devnet) clone + generated manifests/runtime state
+/.decker
+
 # editors
 .code
 .idea
diff --git a/README.md b/README.md
index c658584bc..d8714b85b 100644
--- a/README.md
+++ b/README.md
@@ -109,7 +109,7 @@ This runs both unit tests and integration tests.
 
 ## Local Devnet
 
-Local development environment setup and configuration files can be found in [`local-testing/README.md`](./local-testing/README.md).
+Local devnet setup via [decker](https://github.com/flashbots/decker) is documented in [`local-testing/README.md`](./local-testing/README.md).
 
 ## Running GitHub actions locally
 
diff --git a/decker.ts b/decker.ts
new file mode 100644
index 000000000..9500236e2
--- /dev/null
+++ b/decker.ts
@@ -0,0 +1,42 @@
+// decker (https://github.com/flashbots/decker) manifest for op-rbuilder's local
+// devnet. See local-testing/README.md for quickstart.
+
+import { recipe as opstackRecipe, type OpstackOptions } from "./.decker/recipes/opstack.ts";
+import type { DeckerProject } from "./.decker/utils/manifest.ts";
+import type { Recipe } from "./.decker/utils/types.ts";
+import { obsPods } from "./local-testing/decker/obs.ts";
+
+const options: OpstackOptions = {
+  // Run op-rbuilder behind rollup-boost
+  externalBuilder: "op-rbuilder",
+  // Host process instead of pinned op-rbuilder container
+  // Use `just devnet` or `make op-rbuilder-profiling` to compile binary.
+  builderBinary: "./target/profiling/op-rbuilder",
+  // Karst needs 1s+ blocks for local iteration.
+  l2BlockTime: 1,
+  flashblocks: { blockTimeMs: 200, endBufferMs: 75, sendOffsetMs: -30, continuousBuild: true },
+  chainMonitor: true,
+};
+
+// Builder's RPC port: decker's op-rbuilder container/process
+// prototype hardcodes rpc=9645 (authrpc=9651, metrics=6062) with no options
+// surface (recipe or prototype-override) to repin it to builder-playground's
+// old :2222 without risking a mismatch between the port it actually binds and
+// what other services resolve by name so :9645 is the port to use everywhere
+// for this devnet.
+const opstack = opstackRecipe(options);
+
+// Prometheus + Grafana appended on top of the opstack recipe's own pods
+// (see local-testing/decker/obs.ts).
+const recipe: Recipe = { ...opstack, pods: [...opstack.pods, ...obsPods(opstack)] };
+
+export const project: DeckerProject = {
+  decker: {
+    source: "https://github.com/flashbots/decker.git",
+    ref: "main",
+    into: ".decker",
+  },
+  recipe,
+  // Docker instead of podman (no rootless podman socket available):
+  // target: { pods: "docker-compose" },
+};
diff --git a/justfile b/justfile
index 23c05d476..9f2affab0 100644
--- a/justfile
+++ b/justfile
@@ -1,3 +1,9 @@
+# Build profiling op-rbuilder binary and start the decker local devnet
+# (see local-testing/README.md; requires `decker` CLI on PATH)
+devnet:
+    make op-rbuilder-profiling FEATURES=telemetry,loki
+    decker start
+
 # Build and run op-rbuilder in playground mode for testing
 run-playground:
     cargo build --bin op-rbuilder -p op-rbuilder
diff --git a/local-testing/README.md b/local-testing/README.md
index 0e640518b..9b97c37b0 100644
--- a/local-testing/README.md
+++ b/local-testing/README.md
@@ -1,14 +1,106 @@
 # Local Dev Environment
 
-This directory contains local development environment configuration for `op-rbuilder`.
+Local devnet configuration for `op-rbuilder`, powered by [decker](https://github.com/flashbots/decker). [builder-playground](https://github.com/flashbots/builder-playground) (`local-testing/playground.yaml`) is kept working as a legacy fallback, see [Legacy appendix](#legacy-builder-playground-deprecated).
 
 ## Prerequisites
 
+- **podman**, with its (rootless) API socket running. For docker instead, uncomment the `target: { pods: "docker-compose" }` line at the bottom of `decker.ts`.
+- **decker** CLI:
+  ```bash
+  curl -sSfL https://raw.githubusercontent.com/flashbots/decker/main/install.sh | bash
+  ```
+- **process-compose**: `op-rbuilder` runs as a host process here, which decker drives through its `process-compose` renderer.
+- [flashbots/contender](https://github.com/flashbots/contender), for traffic generation.
+
+## Quickstart
+
+**First time only**: clone decker into `.decker/` before anything else:
+
+```bash
+git clone https://github.com/flashbots/decker.git .decker
+```
+
+From the repository root:
+
+```bash
+just devnet
+```
+
+This builds the profiling `op-rbuilder` binary and runs `decker start` against the `.decker/` clone above, bringing the whole stack up.
+
+Or alternatively:
+
+```bash
+make op-rbuilder-profiling FEATURES=telemetry,loki
+decker start   # fg, Ctrl+C to stop; use `decker up` + `decker down` to detach
+```
+
+See `decker.ts` for the exact recipe options (fork, L2 block time, flashblocks config, chain-monitor, observability).
+
+## Generate Local Traffic
+
+```bash
+contender spam --tps 50 -r http://localhost:9645 --optimism --min-balance 0.14eth --forever
+```
+
+You should start to see blocks being built and landed on-chain with `contender` transactions.
+
+## Send a Test Transaction
+
+```bash
+decker test --rpc 9645
+```
+
+(`--rpc` accepts a bare port as shorthand for `http://localhost:<port>`, or a full URL.)
+
+## Services
+
+| Service | Port | Notes |
+|---|---|---|
+| op-rbuilder RPC | `9645` | decker's fixed port |
+| op-rbuilder authrpc | `9651` | rollup-boost engine-API |
+| op-rbuilder metrics | `6062` | |
+| op-rbuilder flashblocks (ws) | `1111` | `ws://localhost:1111` |
+| chain-monitor | `8087` | `http://localhost:8087/metrics` |
+| Prometheus | `9009` | scrapes op-rbuilder + chain-monitor metrics |
+| Grafana | `3000` | `http://localhost:3000`, anonymous Admin (no login) |
+| L1 EL (`el-1`) RPC | `8545` | |
+| L2 sequencer EL RPC | `9545` | fallback target rollup-boost |
+| L1 explorer (Blockscout) | `3002` | `http://localhost:3002` |
+| L2 explorer (Blockscout) | `3003` | `http://localhost:3003` |
+| Pod logs (Dozzle) | `18080` | podman only; under `docker-compose` use `decker attach` for logs |
+
+## Observability
+
+Provisioned by `local-testing/decker/obs.ts`:
+
+- **Prometheus** (`:9009`) scrapes `op-rbuilder`'s metrics.
+- **Grafana** (`:3000`) provisioned with op-rbuilder local dashboard.
+
+**Deferred**: Loki, Tempo and Alloy. decker has no container prototypes for them yet.
+
+## Builder-Only Restart Loop
+
+To iterate on `op-rbuilder` itself without tearing down the rest of the devnet: stop decker's own builder process (it holds `:9645`/`:9651`), rebuild, then run the binary directly from the repository root; it auto-detects the running devnet's artifacts:
+
+```bash
+make op-rbuilder-profiling FEATURES=telemetry,loki
+./target/profiling/op-rbuilder node --builder.playground
+```
+
+A bare `--builder.playground` resolves `./.decker/runtime/artifacts` first, falling back to the legacy `$HOME/.local/state/builder-playground/devnet` if that doesn't exist.
+
+## Karst
+
+The devnet defaults to the `karst` L2 fork, which requires `op-reth` v2.3.x dependency.
+
+## Legacy: builder-playground (deprecated)
+
+Kept working during the migration to decker above; do not add anything new here.
+
 1. [flashbots/builder-playground](https://github.com/flashbots/builder-playground).
 1. [flashbots/contender](https://github.com/flashbots/contender).
 
-## Start Local Devnet
-
 From the repository root:
 
 ```bash
@@ -31,20 +123,16 @@ Services:
 
 Logs can be found at `$HOME/.local/state/builder-playground/sessions/latest/logs/`
 
-## Generate Local Traffic
-
-Run `contender`:
+Generate local traffic with `contender`:
 
 ```bash
 contender spam --tps 50 -r http://localhost:2222 --optimism --min-balance 0.14eth --forever
 ```
 
-You should start to see blocks being built and landed on-chain with `contender` transactions.
-
-Alternatively, send a single test transaction:
+Send a single test transaction (note the `--rpc` flag — a bare target URL is silently ignored):
 
 ```bash
-builder-playground test http://localhost:2222 --timeout 30s --retries 10
+builder-playground test --rpc http://localhost:2222 --timeout 30s --retries 10
 ```
 
 `op-rbuilder` automatically detects settings and ports from the running playground via `--builder.playground`.
diff --git a/local-testing/decker/obs.ts b/local-testing/decker/obs.ts
new file mode 100644
index 000000000..0065e34c3
--- /dev/null
+++ b/local-testing/decker/obs.ts
@@ -0,0 +1,83 @@
+// Observability overlay for decker.ts: Prometheus scraping op-rbuilder (+
+// chain-monitor, when enabled) and Grafana provisioning.
+//
+// Loki/Tempo/Alloy are deferred and will be wired as follow up.
+import type { ContainerDef, ContainerResult, Ctx, Pod, Prototype, Recipe } from "../../.decker/utils/types.ts";
+
+// Resolved against this module's file.
+const GRAFANA_DIR = new URL("../grafana/", import.meta.url);
+
+function readLocal(relPath: string): string {
+  return Deno.readTextFileSync(new URL(relPath, GRAFANA_DIR));
+}
+
+// Read once at module load instead of per-render.
+const DASHBOARD_PROVIDER_YML = readLocal("dashboards.yaml");
+const OP_RBUILDER_DASHBOARD_JSON = readLocal("dashboards/op-rbuilder.json");
+
+const GRAFANA_HTTP_PORT = 3000;
+
+function buildGrafanaContainer(def: ContainerDef, ctx: Ctx): ContainerResult {
+  const prometheusRef = def.refs?.prometheus;
+  if (!prometheusRef) throw new Error(`grafana ${def.name}: missing refs.prometheus`);
+
+  const datasourcesYml = `apiVersion: 1
+datasources:
+  - name: Prometheus
+    type: prometheus
+    access: proxy
+    url: ${ctx.url(prometheusRef, "http")}
+    uid: prometheus
+    isDefault: true
+    editable: false
+    jsonData:
+      timeInterval: "5s"
+      httpMethod: POST
+`;
+
+  return {
+    container: {
+      image: "docker.io/grafana/grafana:13.0.1",
+      env: {
+        // Passwordless dev access
+        GF_AUTH_ANONYMOUS_ENABLED: "true",
+        GF_AUTH_ANONYMOUS_ORG_ROLE: "Admin",
+        GF_AUTH_DISABLE_LOGIN_FORM: "true",
+        GF_AUTH_BASIC_ENABLED: "false",
+        GF_USERS_DEFAULT_THEME: "dark",
+        GF_LOG_LEVEL: "warn",
+      },
+      ports: { http: GRAFANA_HTTP_PORT },
+    },
+    configs: [
+      { filename: "datasources.yml", content: datasourcesYml, mountPath: "/etc/grafana/provisioning/datasources/datasources.yml" },
+      { filename: "dashboards.yml", content: DASHBOARD_PROVIDER_YML, mountPath: "/etc/grafana/provisioning/dashboards/dashboards.yml" },
+      { filename: "op-rbuilder.json", content: OP_RBUILDER_DASHBOARD_JSON, mountPath: "/var/lib/grafana/dashboards/op-rbuilder.json" },
+    ],
+  };
+}
+
+const grafanaPrototype: Prototype = {
+  ports: { http: GRAFANA_HTTP_PORT },
+  buildContainer: buildGrafanaContainer,
+  webui: { label: "Grafana (op-rbuilder dashboard)" },
+};
+
+// Appended to the opstack recipe `pods`.
+export function obsPods(base: Recipe): Pod[] {
+  const hasChainMonitor = base.pods.some((p) => p.name === "chain-monitor");
+  const scrape = [
+    { job: "op-rbuilder", ref: "op-rbuilder", port: "metrics" },
+    ...(hasChainMonitor ? [{ job: "chain-monitor", ref: "chain-monitor", port: "http", path: "/metrics" }] : []),
+  ];
+  return [
+    {
+      name: "prometheus",
+      containers: [{ name: "prometheus", prototype: "prometheus", config: { scrape } }],
+    },
+    {
+      name: "grafana",
+      containers: [{ name: "grafana", prototype: grafanaPrototype, refs: { prometheus: "prometheus" } }],
+    },
+  ];
+}