MCP Browser Automation Server

Instructions

Implementation Reference

• src/toolsHandler.ts:274-318 (handler)

  Handler function for 'playwright_evaluate' tool: executes JavaScript using page.evaluate, overrides console methods to capture logs, returns execution result and console output.

  case "playwright_evaluate":
    try {
      const result = await page!.evaluate((script) => {
        const logs: string[] = [];
        const originalConsole = { ...console };
  
        ['log', 'info', 'warn', 'error'].forEach(method => {
          (console as any)[method] = (...args: any[]) => {
            logs.push(`[${method}] ${args.join(' ')}`);
            (originalConsole as any)[method](...args);
          };
        });
  
        try {
          const result = eval(script);
          Object.assign(console, originalConsole);
          return { result, logs };
        } catch (error) {
          Object.assign(console, originalConsole);
          throw error;
        }
      }, args.script);
  
      return {
        toolResult: {
          content: [
            {
              type: "text",
              text: `Execution result:\n${JSON.stringify(result.result, null, 2)}\n\nConsole output:\n${result.logs.join('\n')}`,
            },
          ],
          isError: false,
        },
      };
    } catch (error) {
      return {
        toolResult: {
          content: [{
            type: "text",
            text: `Script execution failed: ${(error as Error).message}`,
          }],
          isError: true,
        },
      };
    }

• src/tools.ts:79-89 (schema)

  Tool schema definition including name, description, and input schema requiring a 'script' string parameter.

  {
    name: "playwright_evaluate",
    description: "Execute JavaScript in the browser console",
    inputSchema: {
      type: "object",
      properties: {
        script: { type: "string", description: "JavaScript code to execute" },
      },
      required: ["script"],
    },
  },

• src/tools.ts:152-160 (helper)

  Helper constant listing browser tools including 'playwright_evaluate' to conditionally launch browser in handleToolCall.

  export const BROWSER_TOOLS = [
    "playwright_navigate",
    "playwright_screenshot",
    "playwright_click",
    "playwright_fill",
    "playwright_select",
    "playwright_hover",
    "playwright_evaluate"
  ];

• src/index.ts:22-26 (registration)

  Registration of all tools (including 'playwright_evaluate') via createToolDefinitions and setupRequestHandlers on the MCP server.

  // Create tool definitions
  const TOOLS = createToolDefinitions();
  
  // Setup request handlers
  setupRequestHandlers(server, TOOLS);