modelcontextprotocol · cliffhall · Jun 18, 2025 · Jun 16, 2025 · Jun 16, 2025 · Jun 16, 2025
diff --git a/README.md b/README.md
@@ -148,9 +148,9 @@ The MCP Inspector proxy server requires authentication by default. When starting
    http://localhost:6274/?MCP_PROXY_AUTH_TOKEN=3a1c267fad21f7150b7d624c160b7f09b0b8c4f623c7107bbf13378f051538d4
 ```
 
-This token must be included as a Bearer token in the Authorization header for all requests to the server. When authentication is enabled, auto-open is disabled by default to ensure you use the secure URL.
+This token must be included as a Bearer token in the Authorization header for all requests to the server. The inspector will automatically open your browser with the token pre-filled in the URL.
 
-**Recommended: Use the pre-filled URL** - Click or copy the link shown in the console to open the inspector with the token already configured.
+**Automatic browser opening** - The inspector now automatically opens your browser with the token pre-filled in the URL when authentication is enabled.
 
 **Alternative: Manual configuration** - If you already have the inspector open:
 
@@ -188,13 +188,13 @@ ALLOWED_ORIGINS=http://localhost:6274,http://127.0.0.1:6274,http://localhost:800
 
 The MCP Inspector supports the following configuration settings. To change them, click on the `Configuration` button in the MCP Inspector UI:
 
-| Setting                                 | Description                                                                                                   | Default |
-| --------------------------------------- | ------------------------------------------------------------------------------------------------------------- | ------- |
-| `MCP_SERVER_REQUEST_TIMEOUT`            | Timeout for requests to the MCP server (ms)                                                                   | 10000   |
-| `MCP_REQUEST_TIMEOUT_RESET_ON_PROGRESS` | Reset timeout on progress notifications                                                                       | true    |
-| `MCP_REQUEST_MAX_TOTAL_TIMEOUT`         | Maximum total timeout for requests sent to the MCP server (ms) (Use with progress notifications)              | 60000   |
-| `MCP_PROXY_FULL_ADDRESS`                | Set this if you are running the MCP Inspector Proxy on a non-default address. Example: http://10.1.1.22:5577  | ""      |
-| `MCP_AUTO_OPEN_ENABLED`                 | Enable automatic browser opening when inspector starts. Only as environment var, not configurable in browser. | true    |
+| Setting                                 | Description                                                                                                                                       | Default |
+| --------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------- | ------- |
+| `MCP_SERVER_REQUEST_TIMEOUT`            | Timeout for requests to the MCP server (ms)                                                                                                       | 10000   |
+| `MCP_REQUEST_TIMEOUT_RESET_ON_PROGRESS` | Reset timeout on progress notifications                                                                                                           | true    |
+| `MCP_REQUEST_MAX_TOTAL_TIMEOUT`         | Maximum total timeout for requests sent to the MCP server (ms) (Use with progress notifications)                                                  | 60000   |
+| `MCP_PROXY_FULL_ADDRESS`                | Set this if you are running the MCP Inspector Proxy on a non-default address. Example: http://10.1.1.22:5577                                      | ""      |
+| `MCP_AUTO_OPEN_ENABLED`                 | Enable automatic browser opening when inspector starts (works with authentication enabled). Only as environment var, not configurable in browser. | true    |
 
 These settings can be adjusted in real-time through the UI and will persist across sessions.
 

diff --git a/client/bin/start.js b/client/bin/start.js
@@ -2,22 +2,175 @@
 
 import open from "open";
 import { resolve, dirname } from "path";
-import { spawnPromise } from "spawn-rx";
+import { spawnPromise, spawn } from "spawn-rx";
 import { fileURLToPath } from "url";
+import { randomBytes } from "crypto";
 
 const __dirname = dirname(fileURLToPath(import.meta.url));
 
 function delay(ms) {
   return new Promise((resolve) => setTimeout(resolve, ms, true));
 }
 
+async function startDevServer(serverOptions) {
+  const { SERVER_PORT, CLIENT_PORT, sessionToken, envVars, abort } =
+    serverOptions;
+  const serverCommand = "npx";
+  const serverArgs = ["tsx", "watch", "--clear-screen=false", "src/index.ts"];
+  const isWindows = process.platform === "win32";
+
+  const spawnOptions = {
+    cwd: resolve(__dirname, "../..", "server"),
+    env: {
+      ...process.env,
+      PORT: SERVER_PORT,
+      CLIENT_PORT: CLIENT_PORT,
+      MCP_PROXY_TOKEN: sessionToken,
+      MCP_ENV_VARS: JSON.stringify(envVars),
+    },
+    signal: abort.signal,
+    echoOutput: true,
+  };
+
+  // For Windows, we need to use stdin: 'ignore' to simulate < NUL
+  if (isWindows) {
+    spawnOptions.stdin = "ignore";
+  }
+
+  const server = spawn(serverCommand, serverArgs, spawnOptions);
+
+  // Give server time to start
+  const serverOk = await Promise.race([
+    new Promise((resolve) => {
+      server.subscribe({
+        complete: () => resolve(false),
+        error: () => resolve(false),
+        next: () => {}, // We're using echoOutput
+      });
+    }),
+    delay(3000).then(() => true),
+  ]);
+
+  return { server, serverOk };
+}
+
+async function startProdServer(serverOptions) {
+  const {
+    SERVER_PORT,
+    CLIENT_PORT,
+    sessionToken,
+    envVars,
+    abort,
+    command,
+    mcpServerArgs,
+  } = serverOptions;
+  const inspectorServerPath = resolve(
+    __dirname,
+    "../..",
+    "server",
+    "build",
+    "index.js",
+  );
+
+  const server = spawnPromise(
+    "node",
+    [
+      inspectorServerPath,
+      ...(command ? [`--env`, command] : []),
+      ...(mcpServerArgs ? [`--args=${mcpServerArgs.join(" ")}`] : []),
+    ],
+    {
+      env: {
+        ...process.env,
+        PORT: SERVER_PORT,
+        CLIENT_PORT: CLIENT_PORT,
+        MCP_PROXY_TOKEN: sessionToken,
+        MCP_ENV_VARS: JSON.stringify(envVars),
+      },
+      signal: abort.signal,
+      echoOutput: true,
+    },
+  );
+
+  // Make sure server started before starting client
+  const serverOk = await Promise.race([server, delay(2 * 1000)]);
+
+  return { server, serverOk };
+}
+
+async function startDevClient(clientOptions) {
+  const { CLIENT_PORT, authDisabled, sessionToken, abort, cancelled } =
+    clientOptions;
+  const clientCommand = "npx";
+  const clientArgs = ["vite", "--port", CLIENT_PORT];
+
+  const client = spawn(clientCommand, clientArgs, {
+    cwd: resolve(__dirname, ".."),
+    env: { ...process.env, PORT: CLIENT_PORT },
+    signal: abort.signal,
+    echoOutput: true,
+  });
+
+  // Auto-open browser after vite starts
+  if (process.env.MCP_AUTO_OPEN_ENABLED !== "false") {
+    const url = authDisabled
+      ? `http://127.0.0.1:${CLIENT_PORT}`
+      : `http://127.0.0.1:${CLIENT_PORT}/?MCP_PROXY_AUTH_TOKEN=${sessionToken}`;
+
+    // Give vite time to start before opening browser
+    setTimeout(() => {
+      open(url);
+      console.log(`\n🔗 Opening browser at: ${url}\n`);
+    }, 3000);
+  }
+
+  await new Promise((resolve) => {
+    client.subscribe({
+      complete: resolve,
+      error: (err) => {
+        if (!cancelled || process.env.DEBUG) {
+          console.error("Client error:", err);
+        }
+        resolve(null);
+      },
+      next: () => {}, // We're using echoOutput
+    });
+  });
+}
+
+async function startProdClient(clientOptions) {
+  const { CLIENT_PORT, authDisabled, sessionToken, abort } = clientOptions;
+  const inspectorClientPath = resolve(
+    __dirname,
+    "../..",
+    "client",
+    "bin",
+    "client.js",
+  );
+
+  // Auto-open browser with token
+  if (process.env.MCP_AUTO_OPEN_ENABLED !== "false") {
+    const url = authDisabled
+      ? `http://127.0.0.1:${CLIENT_PORT}`
+      : `http://127.0.0.1:${CLIENT_PORT}/?MCP_PROXY_AUTH_TOKEN=${sessionToken}`;
+    open(url);
+  }
+
+  await spawnPromise("node", [inspectorClientPath], {
+    env: { ...process.env, PORT: CLIENT_PORT },
+    signal: abort.signal,
+    echoOutput: true,
+  });
+}
+
 async function main() {
   // Parse command line arguments
   const args = process.argv.slice(2);
   const envVars = {};
   const mcpServerArgs = [];
   let command = null;
   let parsingFlags = true;
+  let isDev = false;
 
   for (let i = 0; i < args.length; i++) {
     const arg = args[i];
@@ -27,6 +180,11 @@ async function main() {
       continue;
     }
 
+    if (parsingFlags && arg === "--dev") {
+      isDev = true;
+      continue;
+    }
+
     if (parsingFlags && arg === "-e" && i + 1 < args.length) {
       const envVar = args[++i];
       const equalsIndex = envVar.indexOf("=");
@@ -38,34 +196,25 @@ async function main() {
       } else {
         envVars[envVar] = "";
       }
-    } else if (!command) {
+    } else if (!command && !isDev) {
       command = arg;
-    } else {
+    } else if (!isDev) {
       mcpServerArgs.push(arg);
     }
   }
 
-  const inspectorServerPath = resolve(
-    __dirname,
-    "../..",
-    "server",
-    "build",
-    "index.js",
-  );
-
-  // Path to the client entry point
-  const inspectorClientPath = resolve(
-    __dirname,
-    "../..",
-    "client",
-    "bin",
-    "client.js",
-  );
-
   const CLIENT_PORT = process.env.CLIENT_PORT ?? "6274";
   const SERVER_PORT = process.env.SERVER_PORT ?? "6277";
 
-  console.log("Starting MCP inspector...");
+  console.log(
+    isDev
+      ? "Starting MCP inspector in development mode..."
+      : "Starting MCP inspector...",
+  );
+
+  // Generate session token for authentication
+  const sessionToken = randomBytes(32).toString("hex");
+  const authDisabled = !!process.env.DANGEROUSLY_OMIT_AUTH;
 
   const abort = new AbortController();
 
@@ -74,42 +223,41 @@ async function main() {
     cancelled = true;
     abort.abort();
   });
+
   let server, serverOk;
+
   try {
-    server = spawnPromise(
-      "node",
-      [
-        inspectorServerPath,
-        ...(command ? [`--env`, command] : []),
-        ...(mcpServerArgs ? [`--args=${mcpServerArgs.join(" ")}`] : []),
-      ],
-      {
-        env: {
-          ...process.env,
-          PORT: SERVER_PORT,
-          MCP_ENV_VARS: JSON.stringify(envVars),
-        },
-        signal: abort.signal,
-        echoOutput: true,
-      },
-    );
+    const serverOptions = {
+      SERVER_PORT,
+      CLIENT_PORT,
+      sessionToken,
+      envVars,
+      abort,
+      command,
+      mcpServerArgs,
+    };
 
-    // Make sure server started before starting client
-    serverOk = await Promise.race([server, delay(2 * 1000)]);
+    const result = isDev
+      ? await startDevServer(serverOptions)
+      : await startProdServer(serverOptions);
+
+    server = result.server;
+    serverOk = result.serverOk;
   } catch (error) {}
 
   if (serverOk) {
     try {
-      // Only auto-open when auth is disabled
-      const authDisabled = !!process.env.DANGEROUSLY_OMIT_AUTH;
-      if (process.env.MCP_AUTO_OPEN_ENABLED !== "false" && authDisabled) {
-        open(`http://127.0.0.1:${CLIENT_PORT}`);
-      }
-      await spawnPromise("node", [inspectorClientPath], {
-        env: { ...process.env, PORT: CLIENT_PORT },
-        signal: abort.signal,
-        echoOutput: true,
-      });
+      const clientOptions = {
+        CLIENT_PORT,
+        authDisabled,
+        sessionToken,
+        abort,
+        cancelled,
+      };
+
+      await (isDev
+        ? startDevClient(clientOptions)
+        : startProdClient(clientOptions));
     } catch (e) {
       if (!cancelled || process.env.DEBUG) throw e;
     }

diff --git a/package.json b/package.json
@@ -27,8 +27,8 @@
     "build-client": "cd client && npm run build",
     "build-cli": "cd cli && npm run build",
     "clean": "rimraf ./node_modules ./client/node_modules ./cli/node_modules ./build ./client/dist ./server/build ./cli/build ./package-lock.json && npm install",
-    "dev": "concurrently \"cd client && npm run dev\" \"cd server && npm run dev\"",
-    "dev:windows": "concurrently \"cd client && npm run dev\" \"cd server && npm run dev:windows\"",
+    "dev": "node client/bin/start.js --dev",
+    "dev:windows": "node client/bin/start.js --dev",
     "start": "node client/bin/start.js",
     "start-server": "cd server && npm run start",
     "start-client": "cd client && npm run preview",

diff --git a/server/src/index.ts b/server/src/index.ts
@@ -89,7 +89,9 @@ app.use((req, res, next) => {
 const webAppTransports: Map<string, Transport> = new Map<string, Transport>(); // Web app transports by web app sessionId
 const serverTransports: Map<string, Transport> = new Map<string, Transport>(); // Server Transports by web app sessionId
 
-const sessionToken = randomBytes(32).toString("hex");
+// Use provided token from environment or generate a new one
+const sessionToken =
+  process.env.MCP_PROXY_TOKEN || randomBytes(32).toString("hex");
 const authDisabled = !!process.env.DANGEROUSLY_OMIT_AUTH;
 
 // Origin validation middleware to prevent DNS rebinding attacks
@@ -544,7 +546,7 @@ server.on("listening", () => {
     const clientPort = process.env.CLIENT_PORT || "6274";
     const clientUrl = `http://localhost:${clientPort}/?MCP_PROXY_AUTH_TOKEN=${sessionToken}`;
     console.log(
-      `\n🔗 Open inspector with token pre-filled:\n   ${clientUrl}\n   (Auto-open is disabled when authentication is enabled)\n`,
+      `\n🔗 Open inspector with token pre-filled:\n   ${clientUrl}\n`,
     );
   } else {
     console.log(