diff --git a/README.md b/README.md
index 5a52d5cd..0c8600d0 100644
--- a/README.md
+++ b/README.md
@@ -129,6 +129,22 @@ Learn more about our design decisions and system components in the **[Architectu
 
 ---
 
+## 🔀 Multi-Instance Development
+
+Run multiple isolated dev instances on one machine for parallel feature work:
+
+```bash
+# Instance 0 (default)
+just dev
+
+# Instance 1 — offset ports (frontend :5273, backend :3311)
+SHIPSEC_INSTANCE=1 just dev
+```
+
+Each instance gets its own frontend port, backend port, database, and Temporal namespace while sharing a single Docker infra stack. See [Multi-Instance Development Guide](docs/MULTI-INSTANCE-DEV.md) for full details.
+
+---
+
 ## ✍️ Contributing
 
 We welcome contributions to the management plane, worker logic, or new security components.
diff --git a/docs/MULTI-INSTANCE-DEV.md b/docs/MULTI-INSTANCE-DEV.md
index c9547898..acd7ed7f 100644
--- a/docs/MULTI-INSTANCE-DEV.md
+++ b/docs/MULTI-INSTANCE-DEV.md
@@ -78,7 +78,7 @@ http://localhost:5273        # frontend
 http://localhost:3311/api    # backend API
 ```
 
-The Vite dev server proxies `/api` calls to the correct backend port automatically via `VITE_API_URL`.
+The Vite dev server proxies `/api` calls to the correct backend port automatically (computed from `SHIPSEC_INSTANCE` in `vite.config.ts`).
 
 ## Commands
 
diff --git a/frontend/vite.config.ts b/frontend/vite.config.ts
index 109c24a0..93ba4362 100644
--- a/frontend/vite.config.ts
+++ b/frontend/vite.config.ts
@@ -2,7 +2,9 @@ import { defineConfig } from 'vite';
 import react from '@vitejs/plugin-react';
 import path from 'path';
 
-const apiTarget = process.env.VITE_API_URL || 'http://localhost:3211';
+const instance = parseInt(process.env.SHIPSEC_INSTANCE || '0', 10);
+const frontendPort = 5173 + instance * 100;
+const backendPort = 3211 + instance * 100;
 
 // https://vitejs.dev/config/
 export default defineConfig({
@@ -23,11 +25,13 @@ export default defineConfig({
   },
   server: {
     host: '0.0.0.0',
+    port: frontendPort,
+    strictPort: true,
     open: false,
     allowedHosts: ['studio.shipsec.ai', 'frontend'],
     proxy: {
       '/api': {
-        target: apiTarget,
+        target: `http://localhost:${backendPort}`,
         changeOrigin: true,
         secure: false,
       },
diff --git a/pm2.config.cjs b/pm2.config.cjs
index f9b31dbd..ac8ebf61 100644
--- a/pm2.config.cjs
+++ b/pm2.config.cjs
@@ -331,14 +331,12 @@ module.exports = {
       name: `shipsec-frontend-${instanceNum}`,
       cwd: __dirname + '/frontend',
       script: 'bun',
-      // Ensure each instance binds to its own Vite port (default is 5173).
-      args: ['run', 'dev', '--', '--port', String(getInstancePort(5173, instanceNum)), '--strictPort'],
+      args: 'run dev',
       env_file: resolveEnvFile('frontend', instanceNum),
       env: {
         ...loadFrontendEnv(resolveEnvFile('frontend', instanceNum)),
         ...currentEnvConfig,
-        // Ensure Vite proxy targets the correct instance backend
-        VITE_API_URL: `http://localhost:${getInstancePort(3211, instanceNum)}`,
+        SHIPSEC_INSTANCE: instanceNum,
       },
       watch: !isProduction ? ['src'] : false,
       ignore_watch: ['node_modules', 'dist', '*.log'],