diff --git a/.changeset/swingset-auto-port.md b/.changeset/swingset-auto-port.md
new file mode 100644
index 00000000000..a845151cc84
--- /dev/null
+++ b/.changeset/swingset-auto-port.md
@@ -0,0 +1,2 @@
+---
+---
diff --git a/packages/swingset/CLAUDE.md b/packages/swingset/CLAUDE.md
index da4b8e4ba62..fff87489c40 100644
--- a/packages/swingset/CLAUDE.md
+++ b/packages/swingset/CLAUDE.md
@@ -9,7 +9,7 @@ This file provides guidance to Coding Agents when working with code in this repo
 Run from the monorepo root or scope with `--filter @clerk/swingset`:
 
 ```
-pnpm run dev:swingset                # next dev on port 6006
+pnpm run dev:swingset                # next dev on $PORT (default 6006), or the next free port
 pnpm build --filter @clerk/swingset  # next build
 pnpm format --filter @clerk/swingset # format-package.mjs (--check for CI)
 ```
diff --git a/packages/swingset/README.md b/packages/swingset/README.md
index 9fe2095cfec..8f7cb7a0000 100644
--- a/packages/swingset/README.md
+++ b/packages/swingset/README.md
@@ -1,6 +1,6 @@
 # Swingset
 
-Component explorer for the Mosaic design system. Runs at http://localhost:6006.
+Component explorer for the Mosaic design system. Runs at http://localhost:6006, or the next free port if 6006 is taken.
 
 ## Dev
 
diff --git a/packages/swingset/package.json b/packages/swingset/package.json
index dec1eefe6b9..72d455974e8 100644
--- a/packages/swingset/package.json
+++ b/packages/swingset/package.json
@@ -5,7 +5,7 @@
   "type": "module",
   "scripts": {
     "build": "next build",
-    "dev": "next dev --port 6006",
+    "dev": "node scripts/dev.mjs",
     "format": "node ../../scripts/format-package.mjs",
     "format:check": "node ../../scripts/format-package.mjs --check"
   },
@@ -42,6 +42,7 @@
     "@tailwindcss/postcss": "^4.0.0",
     "@types/react": "catalog:react",
     "@types/react-dom": "catalog:react",
+    "get-port": "^5.1.1",
     "rehype-slug": "^6.0.0",
     "remark-gfm": "^4.0.0",
     "shadcn": "^4.10.0",
diff --git a/packages/swingset/scripts/dev.mjs b/packages/swingset/scripts/dev.mjs
new file mode 100644
index 00000000000..00ef69ba0f8
--- /dev/null
+++ b/packages/swingset/scripts/dev.mjs
@@ -0,0 +1,21 @@
+import { spawn } from 'node:child_process';
+
+import getPort from 'get-port';
+
+const start = Number(process.env.PORT) || 6006;
+const port = await getPort({ port: getPort.makeRange(start, start + 100) });
+
+const child = spawn('next', ['dev', '--port', String(port), ...process.argv.slice(2)], { stdio: 'inherit' });
+
+for (const signal of ['SIGINT', 'SIGTERM']) {
+  process.on(signal, () => child.kill(signal));
+}
+
+child.on('exit', (code, signal) => {
+  if (signal) {
+    process.removeAllListeners(signal);
+    process.kill(process.pid, signal);
+  } else {
+    process.exit(code ?? 0);
+  }
+});
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 707a0c331b4..bd809f40daa 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -1205,6 +1205,9 @@ importers:
       '@types/react-dom':
         specifier: catalog:react
         version: 18.3.7(@types/react@18.3.28)
+      get-port:
+        specifier: ^5.1.1
+        version: 5.1.1
       rehype-slug:
         specifier: ^6.0.0
         version: 6.0.0