browser_evaluate

Instructions

Implementation Reference

• src/executor.ts:456-510 (handler)

  The handler function `handleBrowserEvaluate` that executes JavaScript in the browser context via Playwright's `page.evaluate()`. It intercepts console.log/info/warn/error, runs `eval(script)` in the page, and returns both the script result (JSON-stringified) and any console output.

  async function handleBrowserEvaluate(page: Page, args: any): Promise<{ toolResult: CallToolResult }> {
    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: `Script result: ${JSON.stringify(result.result, null, 2)}`,
            },
            {
              type: "text",
              text: `Console output:\n${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:119-129 (schema)

  The input schema definition for 'browser_evaluate' tool, requiring a 'script' string property (JavaScript code to execute).

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

• src/tools.ts:3-12 (registration)

  The tool string 'browser_evaluate' is registered in the BROWSER_TOOLS array which is used by the executor to route tool calls to the browser.

  export const BROWSER_TOOLS = [
    "browser_navigate",
    "browser_screenshot",
    "browser_click",
    "browser_fill",
    "browser_select",
    "browser_hover",
    "browser_evaluate",
    "browser_set_viewport"
  ];

• src/executor.ts:206-207 (registration)

  The switch-case dispatcher in `executeToolCall` that routes the 'browser_evaluate' tool name to the `handleBrowserEvaluate` handler function.

  case "browser_evaluate":
    return await handleBrowserEvaluate(activePage!, args);