Bridge Client API

Overview

The Bridge Client (bridge.js) is automatically injected into HTML responses by the Resource Server. You typically don’t interact with it directly, but understanding its API helps with debugging.

Initialization

The bridge self-initializes when the page loads:

1. Detects the platform (Telegram, LINE, or generic)
2. Establishes WebSocket connection to the Resource Server
3. Monkey-patches window.parent.postMessage
4. Sends ui/initialize handshake
5. Begins forwarding JSON-RPC messages

JSON-RPC Methods

Outgoing (App to Host)

Method	Description
ui/initialize	Handshake — get host context, capabilities
tools/call	Execute an MCP tool
resources/read	Read an MCP resource
ui/open-link	Open an external URL via the platform
ui/message	Send a message to the host
ui/request-display-mode	Request inline, fullscreen, or PiP display

Incoming (Host to App)

Method	Description
ui/notifications/host-context-changed	Theme, viewport, or locale changed
ui/notifications/tool-input	Tool input data from the host
ui/notifications/tool-result	Tool execution result notification
ui/notifications/tool-cancelled	Tool execution was cancelled
ui/resource-teardown	Platform is closing — clean up
tools/call (response)	Tool execution result (JSON-RPC response)
resources/read (response)	Resource content (JSON-RPC response)

Message Routing

The MessageRouter tracks pending requests with a 30-second timeout:

// Internal flow (simplified)
app.postMessage(request)
  -> bridge.js intercepts
  -> router.send(request)
  -> WebSocket.send(JSON.stringify(request))
  -> ... server processes ...
  -> WebSocket.onmessage(response)
  -> router.resolve(response.id, response)
  -> window.dispatchEvent(MessageEvent)