chore: validate start args (#1113)

The `start` command accepts the MCP server CLI options. This PR adds
yargs validation to the start command and re-uses the same yargs
definitions.

Author: OrKoN

src/bin/chrome-devtools.ts

@@ -10,14 +10,14 @@ import process from 'node:process';
 
 import type {Options, PositionalOptions} from 'yargs';
 
-import {parseArguments} from '../cli.js';
+import {cliOptions, parseArguments} from '../cli.js';
 import {
   startDaemon,
   stopDaemon,
   sendCommand,
   handleResponse,
 } from '../daemon/client.js';
-import {isDaemonRunning} from '../daemon/utils.js';
+import {isDaemonRunning, serializeArgs} from '../daemon/utils.js';
 import {logDisclaimers} from '../server.js';
 import {hideBin, yargs, type CallToolResult} from '../third_party/index.js';
 import {VERSION} from '../version.js';
@@ -26,7 +26,7 @@ import {commands} from './cliDefinitions.js';
 
 async function start(args: string[]) {
   const combinedArgs = [...args, ...defaultArgs];
-  await startDaemon([...args, ...defaultArgs]);
+  await startDaemon(combinedArgs);
   logDisclaimers(parseArguments(VERSION, combinedArgs));
 }
 
@@ -50,19 +50,17 @@ y.command(
   'Start or restart chrome-devtools-mcp',
   y =>
     y
-      .help(false) // Disable help for start command to avoid parsing issues with passed args.
+      .options(cliOptions)
       .example(
-        '$0 start --port 8080 --url http://localhost:8080',
-        'Start the server on port 8080 with a specific URL',
+        '$0 start --browserUrl http://localhost:9222',
+        'Start the server connecting to an existing browser',
       )
-      .strict(false), // Don't validate arguments for start, as they are passed through to the daemon.
-  async () => {
+      .strict(),
+  async argv => {
     if (isDaemonRunning()) {
       await stopDaemon();
     }
-    // Extract args after 'start'
-    const startIndex = process.argv.indexOf('start');
-    const args = startIndex !== -1 ? process.argv.slice(startIndex + 1) : [];
+    const args = serializeArgs(cliOptions, argv);
     await start(args);
     process.exit(0);
   },

src/daemon/utils.ts

@@ -9,7 +9,9 @@ import os from 'node:os';
 import path from 'node:path';
 import process from 'node:process';
 
+import type {ParsedArguments} from '../cli.js';
 import {logger} from '../logger.js';
+import type {YargsOptions} from '../third_party/index.js';
 
 export const DAEMON_SCRIPT_PATH = path.join(import.meta.dirname, 'daemon.js');
 export const INDEX_SCRIPT_PATH = path.join(
@@ -97,3 +99,32 @@ export function isDaemonRunning(pid = getDaemonPid()): pid is number {
   }
   return false;
 }
+
+export function serializeArgs(
+  options: Record<string, YargsOptions>,
+  argv: ParsedArguments,
+): string[] {
+  const args: string[] = [];
+  for (const key of Object.keys(options)) {
+    if (argv[key] === undefined || argv[key] === null) {
+      continue;
+    }
+    const value = argv[key];
+    const kebabKey = key.replace(/[A-Z]/g, m => `-${m.toLowerCase()}`);
+
+    if (typeof value === 'boolean') {
+      if (value) {
+        args.push(`--${kebabKey}`);
+      } else {
+        args.push(`--no-${kebabKey}`);
+      }
+    } else if (Array.isArray(value)) {
+      for (const item of value) {
+        args.push(`--${kebabKey}`, String(item));
+      }
+    } else {
+      args.push(`--${kebabKey}`, String(value));
+    }
+  }
+  return args;
+}

tests/daemon/utils.test.ts

@@ -0,0 +1,85 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import assert from 'node:assert';
+import {describe, it} from 'node:test';
+
+import type {ParsedArguments} from '../../src/cli.js';
+import {serializeArgs} from '../../src/daemon/utils.js';
+import type {YargsOptions} from '../../src/third_party/index.js';
+
+describe('serializeArgs', () => {
+  it('should ignore undefined or null values', () => {
+    const options: Record<string, YargsOptions> = {
+      foo: {},
+      bar: {},
+      baz: {},
+    };
+    const argv = {
+      foo: undefined,
+      bar: null,
+      baz: 'value',
+      _: [],
+      $0: 'test',
+    } as unknown as ParsedArguments;
+    const result = serializeArgs(options, argv);
+    assert.deepStrictEqual(result, ['--baz', 'value']);
+  });
+
+  it('should handle boolean values', () => {
+    const options: Record<string, YargsOptions> = {foo: {}, bar: {}};
+    const argv = {
+      foo: true,
+      bar: false,
+      _: [],
+      $0: 'test',
+    } as unknown as ParsedArguments;
+    const result = serializeArgs(options, argv);
+    assert.deepStrictEqual(result, ['--foo', '--no-bar']);
+  });
+
+  it('should handle array values', () => {
+    const options: Record<string, YargsOptions> = {foo: {}};
+    const argv = {
+      foo: ['val1', 'val2'],
+      _: [],
+      $0: 'test',
+    } as unknown as ParsedArguments;
+    const result = serializeArgs(options, argv);
+    assert.deepStrictEqual(result, ['--foo', 'val1', '--foo', 'val2']);
+  });
+
+  it('should handle primitive values', () => {
+    const options: Record<string, YargsOptions> = {foo: {}, bar: {}};
+    const argv = {
+      foo: 'string',
+      bar: 42,
+      _: [],
+      $0: 'test',
+    } as unknown as ParsedArguments;
+    const result = serializeArgs(options, argv);
+    assert.deepStrictEqual(result, ['--foo', 'string', '--bar', '42']);
+  });
+
+  it('should convert camelCase keys to kebab-case', () => {
+    const options: Record<string, YargsOptions> = {
+      camelCaseKey: {},
+      anotherKey: {},
+    };
+    const argv = {
+      camelCaseKey: 'value1',
+      anotherKey: true,
+      _: [],
+      $0: 'test',
+    } as unknown as ParsedArguments;
+    const result = serializeArgs(options, argv);
+    assert.deepStrictEqual(result, [
+      '--camel-case-key',
+      'value1',
+      '--another-key',
+    ]);
+  });
+});