Unify CDP headers parsing and improve error messages

- Remove duplicate CDP headers documentation from README
- Replace manual JSON parsing with parseJsonObject function
- Use InvalidArgumentError for user-friendly error messages
- Maintain consistency with other option parsers like commaSeparatedList

Addresses review feedback on standardizing parse methods.

Author: moritalous

README.md

@@ -233,20 +233,6 @@ state [here](https://playwright.dev/docs/auth).
 }
 ```
 
-#### CDP Headers
-
-When connecting to a CDP endpoint that requires authentication, you can pass headers:
-
-```bash
-npx @playwright/mcp --cdp-endpoint=http://localhost:9222 --cdp-headers='{"Authorization": "Bearer your-token"}'
-```
-
-Or via environment variable:
-```bash
-export PLAYWRIGHT_MCP_CDP_HEADERS='{"Authorization": "Bearer your-token"}'
-npx @playwright/mcp --cdp-endpoint=http://localhost:9222
-```
-
 ### Configuration file
 
 The Playwright MCP server can be configured using a JSON configuration file. You can specify the configuration file

src/config.ts

@@ -18,6 +18,7 @@ import fs from 'fs';
 import os from 'os';
 import path from 'path';
 import { devices } from 'playwright';
+import { InvalidArgumentError } from 'commander';
 import { sanitizeForFilePath } from './utils.js';
 
 import type { Config, ToolCapability } from '../config.js';
@@ -207,7 +208,7 @@ function configFromEnv(): Config {
   options.browser = envToString(process.env.PLAYWRIGHT_MCP_BROWSER);
   options.caps = commaSeparatedList(process.env.PLAYWRIGHT_MCP_CAPS);
   options.cdpEndpoint = envToString(process.env.PLAYWRIGHT_MCP_CDP_ENDPOINT);
-  options.cdpHeaders = parseJsonEnv(process.env.PLAYWRIGHT_MCP_CDP_HEADERS);
+  options.cdpHeaders = parseJsonObject(process.env.PLAYWRIGHT_MCP_CDP_HEADERS);
   options.config = envToString(process.env.PLAYWRIGHT_MCP_CONFIG);
   options.device = envToString(process.env.PLAYWRIGHT_MCP_DEVICE);
   options.executablePath = envToString(process.env.PLAYWRIGHT_MCP_EXECUTABLE_PATH);
@@ -298,17 +299,21 @@ export function semicolonSeparatedList(value: string | undefined): string[] | un
   return value.split(';').map(v => v.trim());
 }
 
-function parseJsonEnv(value: string | undefined): Record<string, string> | undefined {
+export function parseJsonObject(value: string | undefined): Record<string, string> | undefined {
   if (!value)
     return undefined;
   try {
     const parsed = JSON.parse(value);
     if (typeof parsed !== 'object' || parsed === null || Array.isArray(parsed)) {
-      throw new Error('Expected JSON object');
+      throw new InvalidArgumentError('Expected JSON object');
     }
     return parsed;
   } catch (error) {
-    throw new Error(`Invalid JSON in environment variable: ${error}`);
+    if (error instanceof InvalidArgumentError) {
+      throw error;
+    }
+    const errorMessage = error instanceof Error ? error.message : String(error);
+    throw new InvalidArgumentError(`Invalid JSON format: ${errorMessage}`);
   }
 }
 

src/program.ts

@@ -19,7 +19,7 @@ import { program, Option } from 'commander';
 import { startTraceViewerServer } from 'playwright-core/lib/server';
 
 import * as mcpTransport from './mcp/transport.js';
-import { commaSeparatedList, resolveCLIConfig, semicolonSeparatedList } from './config.js';
+import { commaSeparatedList, parseJsonObject, resolveCLIConfig, semicolonSeparatedList } from './config.js';
 import { packageJSON } from './package.js';
 import { createExtensionContextFactory, runWithExtension } from './extension/main.js';
 import { BrowserServerBackend, FactoryList } from './browserServerBackend.js';
@@ -36,7 +36,7 @@ program
     .option('--browser <browser>', 'browser or chrome channel to use, possible values: chrome, firefox, webkit, msedge.')
     .option('--caps <caps>', 'comma-separated list of additional capabilities to enable, possible values: vision, pdf.', commaSeparatedList)
     .option('--cdp-endpoint <endpoint>', 'CDP endpoint to connect to.')
-    .option('--cdp-headers <headers>', 'JSON string of headers to send with CDP connection, e.g. \'{"Authorization": "Bearer token"}\'')
+    .option('--cdp-headers <headers>', 'JSON string of headers to send with CDP connection, e.g. \'{"Authorization": "Bearer token"}\'', parseJsonObject)
     .option('--config <path>', 'path to the configuration file.')
     .option('--device <device>', 'device to emulate, for example: "iPhone 15"')
     .option('--executable-path <path>', 'path to the browser executable.')
@@ -69,17 +69,6 @@ program
         options.caps = 'vision';
       }
 
-      // Parse CDP headers if provided
-      if (options.cdpHeaders) {
-        try {
-          options.cdpHeaders = JSON.parse(options.cdpHeaders);
-        } catch (error) {
-          // eslint-disable-next-line no-console
-          console.error('Invalid JSON format for --cdp-headers:', error);
-          process.exit(1);
-        }
-      }
-
       const config = await resolveCLIConfig(options);
 
       if (options.extension) {

tests/cdp.spec.ts

@@ -106,7 +106,7 @@ test('cdp server with invalid headers JSON', async () => {
   ]);
   expect(result.error).toBeUndefined();
   expect(result.status).toBe(1);
-  expect(result.stderr.toString()).toContain('Invalid JSON format for --cdp-headers');
+  expect(result.stderr.toString()).toContain('option \'--cdp-headers <headers>\' argument \'invalid-json\' is invalid');
 });
 
 // NOTE: Can be removed when we drop Node.js 18 support and changed to import.meta.filename.