mcp-playwright

Instructions

Implementation Reference

• src/tools/browser/useragent.ts:16-39 (handler)

  Handler function that validates the browser's current User-Agent matches the provided argument by evaluating navigator.userAgent on the page.
  async execute(args: CustomUserAgentArgs, context: ToolContext): Promise<ToolResponse> { return this.safeExecute(context, async (page) => { if (!args.userAgent) { return createErrorResponse("Missing required parameter: userAgent must be provided"); } try { const currentUserAgent = await page.evaluate(() => navigator.userAgent); if (currentUserAgent !== args.userAgent) { const messages = [ "Page was already initialized with a different User Agent.", `Requested: ${args.userAgent}`, `Current: ${currentUserAgent}`, ]; return createErrorResponse(messages.join("\n")); } return createSuccessResponse("User Agent validation successful"); } catch (error) { return createErrorResponse(`Failed to validate User Agent: ${(error as Error).message}`); } }); }
• src/tools.ts:374-383 (schema)

  Tool definition with input schema specifying the required 'userAgent' string parameter.
  name: "playwright_custom_user_agent", description: "Set a custom User Agent for the browser", inputSchema: { type: "object", properties: { userAgent: { type: "string", description: "Custom User Agent for the Playwright browser instance" }, }, required: ["userAgent"], }, },
• src/toolHandler.ts:615-616 (registration)

  Switch case in main tool handler that routes calls to the CustomUserAgentTool instance.
  case "playwright_custom_user_agent": return await customUserAgentTool.execute(args, context);
• src/toolHandler.ts:507-507 (helper)

  Conditional logic that passes the userAgent argument to browser launch settings specifically for this tool.
  userAgent: name === "playwright_custom_user_agent" ? args.userAgent : undefined,
• src/tools.ts:507-507 (registration)

  Inclusion in BROWSER_TOOLS array which triggers browser initialization for this tool.
  "playwright_custom_user_agent",