get_accessibility_tree

Instructions

Implementation Reference

• src/tools/accessibility.ts:124-145 (registration)

  Registration of the 'get_accessibility_tree' tool on the MCP server. It registers using server.tool() with name 'get_accessibility_tree', description, Zod schema (selector, tabId, apiKey), and an async handler that delegates to bridge.sendCommand.

  server.tool(
    'get_accessibility_tree',
    'Get the raw accessibility tree as structured JSON. Companion to browser_snapshot which returns formatted text. Optionally filter to a subtree with a selector.',
    {
      selector: z.string().optional().describe('CSS selector to filter to a subtree'),
      tabId: z.number().optional().describe('Target tab ID (defaults to currently active tab)'),
      apiKey: z.string().optional().describe('API key for authentication if enabled'),
    },
    async ({ selector, tabId, apiKey }) => {
      const result = await bridge.sendCommand({
        command: 'get_accessibility_tree',
        params: { selector },
        tabId,
        apiKey,
        timeout: LONG_TIMEOUT,
      });
      if (!result.success) {
        return { content: [{ type: 'text', text: `Error: ${result.error?.message}` }], isError: true };
      }
      return { content: [{ type: 'text', text: JSON.stringify(result.data, null, 2) }] };
    }
  );

• src/tools/accessibility.ts:132-144 (handler)

  Handler function for 'get_accessibility_tree'. It sends a command with name 'get_accessibility_tree' and an optional 'selector' parameter via the WebSocket bridge, then returns the result as formatted JSON.

  async ({ selector, tabId, apiKey }) => {
    const result = await bridge.sendCommand({
      command: 'get_accessibility_tree',
      params: { selector },
      tabId,
      apiKey,
      timeout: LONG_TIMEOUT,
    });
    if (!result.success) {
      return { content: [{ type: 'text', text: `Error: ${result.error?.message}` }], isError: true };
    }
    return { content: [{ type: 'text', text: JSON.stringify(result.data, null, 2) }] };
  }

• src/tools/accessibility.ts:127-131 (schema)

  Input schema for 'get_accessibility_tree': optional 'selector' (CSS selector string), optional 'tabId' (number), and optional 'apiKey' (string).

  {
    selector: z.string().optional().describe('CSS selector to filter to a subtree'),
    tabId: z.number().optional().describe('Target tab ID (defaults to currently active tab)'),
    apiKey: z.string().optional().describe('API key for authentication if enabled'),
  },

• src/websocket-bridge.ts:63-103 (helper)

  WebSocketBridge.sendCommand() which forwards the command (including 'get_accessibility_tree') to the connected Chrome extension via WebSocket and resolves with the response.

  async sendCommand(cmd: BridgeCommand): Promise<BridgeResponse> {
    if (!this.isConnected()) {
      return {
        success: false,
        error: {
          code: 'NOT_CONNECTED',
          message: 'Chrome extension is not connected. Ensure the extension is installed, enabled, and the browser is running.',
        },
      };
    }
  
    const id = crypto.randomUUID();
    const timeout = cmd.timeout ?? DEFAULT_TIMEOUT;
  
    return new Promise<BridgeResponse>((resolve, reject) => {
      const timer = setTimeout(() => {
        this.pending.delete(id);
        resolve({
          success: false,
          error: {
            code: 'TIMEOUT',
            message: `Command '${cmd.command}' timed out after ${timeout}ms`,
          },
        });
      }, timeout);
  
      this.pending.set(id, { resolve, reject, timer });
  
      const message = {
        id,
        type: 'request',
        command: cmd.command,
        params: cmd.params,
        tabId: cmd.tabId,
        apiKey: cmd.apiKey,
        timestamp: Date.now(),
      };
  
      this.client!.send(JSON.stringify(message));
    });
  }

• src/tools/index.ts:18-18 (registration)

  Import of registerAccessibilityTools from ./accessibility.js which registers 'get_accessibility_tree' among other tools.

  import { registerAccessibilityTools } from './accessibility.js';