diff --git a/docs/errors/DF0052.md b/docs/errors/DF0052.md
new file mode 100644
index 00000000..9922ef89
--- /dev/null
+++ b/docs/errors/DF0052.md
@@ -0,0 +1,29 @@
+---
+outline: deep
+---
+
+# DF0052: HTTP Server Failed to Listen
+
+## Message
+
+> Failed to listen on `{host}:{port}`: `{reason}`
+
+## Cause
+
+`startHttpAndWs` tried to bind the HTTP server it owns to `host:port` and the underlying `listen()` call failed — most commonly `EADDRINUSE` (another process, often a previous devframe instance, is already bound to that port) or `EACCES` (insufficient permissions, typically a privileged port). The WS RPC transport is torn down before this error surfaces, so nothing is leaked.
+
+## Example
+
+```ts
+// A previous instance is still bound to 4096:
+// await startHttpAndWs({ context, host: 'localhost', port: 4096 }) → DF0052
+```
+
+## Fix
+
+- Free the port, or pick another via `--port`, `cli.port` / `cli.portRange` on the definition, or `devMiddleware.port` on `viteDevBridge`.
+- The original node error is available as `error.cause` — check `error.cause.code` (e.g. `'EADDRINUSE'`) to branch on the failure kind programmatically.
+
+## Source
+
+- [`packages/devframe/src/node/server.ts`](https://github.com/devframes/devframe/blob/main/packages/devframe/src/node/server.ts) — `startHttpAndWs()` throws this when its owned HTTP server's `listen()` fails.
diff --git a/packages/devframe/src/node/__tests__/server.test.ts b/packages/devframe/src/node/__tests__/server.test.ts
index 0a497730..1888bb5c 100644
--- a/packages/devframe/src/node/__tests__/server.test.ts
+++ b/packages/devframe/src/node/__tests__/server.test.ts
@@ -100,3 +100,19 @@ describe('startHttpAndWs rpcOptions passthrough', () => {
     }
   })
 })
+
+describe('startHttpAndWs listen failures', () => {
+  it('rejects when the port is already taken instead of hanging', async () => {
+    const host = '127.0.0.1'
+    const first = await startHttpAndWs({ context: await createTestContext(), host, port: 0, auth: false })
+
+    try {
+      await expect(
+        startHttpAndWs({ context: await createTestContext(), host, port: first.port, auth: false }),
+      ).rejects.toThrow(expect.objectContaining({ code: 'DF0052' }))
+    }
+    finally {
+      await first.close()
+    }
+  })
+})
diff --git a/packages/devframe/src/node/diagnostics.ts b/packages/devframe/src/node/diagnostics.ts
index f28dfc6e..f16ed74a 100644
--- a/packages/devframe/src/node/diagnostics.ts
+++ b/packages/devframe/src/node/diagnostics.ts
@@ -112,5 +112,9 @@ export const diagnostics = defineDiagnostics({
       why: (p: { port: number }) => `The devframe instance on port ${p.port} has no MCP endpoint.`,
       fix: 'Restart the instance with the --mcp flag (or set `cli.mcp: true` on its definition) to expose its tools, then list instances again.',
     },
+    DF0052: {
+      why: (p: { host: string, port: number, reason: string }) => `Failed to listen on ${p.host}:${p.port}: ${p.reason}`,
+      fix: 'The port is likely already taken by another process (often a previous devframe instance). Free it, or pick another via `--port`, `cli.port` / `cli.portRange` on the definition, or `devMiddleware.port` on `viteDevBridge`. The original node error is available as `error.cause`.',
+    },
   },
 })
diff --git a/packages/devframe/src/node/server.ts b/packages/devframe/src/node/server.ts
index 17c53854..a30965f3 100644
--- a/packages/devframe/src/node/server.ts
+++ b/packages/devframe/src/node/server.ts
@@ -255,9 +255,30 @@ export async function startHttpAndWs(options: StartHttpAndWsOptions): Promise<St
   // Only start listening on a server we created. A shared server is already
   // (or about to be) listening under the caller's control.
   if (ownsHttpServer) {
-    await new Promise<void>((resolveListen) => {
-      httpServer.listen(port, bindHost, () => resolveListen())
-    })
+    try {
+      await new Promise<void>((resolve, reject) => {
+        const onError = (error: Error): void => reject(error)
+        // Without this listener a failed bind emits `error` with nobody
+        // attached — an uncaughtException — and the `listen` callback never
+        // fires, so this promise never settles.
+        httpServer.once('error', onError)
+        httpServer.listen(port, bindHost, () => {
+          httpServer.removeListener('error', onError)
+          resolve()
+        })
+      })
+    }
+    catch (error) {
+      // The WS transport is already attached above, so tear it down before
+      // surfacing the failure rather than leaking it and its peers.
+      await closeWs().catch(() => {})
+      throw diagnostics.DF0052({
+        host: bindHost,
+        port,
+        reason: error instanceof Error ? error.message : String(error),
+        cause: error,
+      })
+    }
   }
 
   const address = httpServer.address()