copilot-mcp

Manages the full lifecycle of Model Context Protocol servers by spawning and monitoring local Node.js processes or connecting to remote Server-Sent Events (SSE) endpoints. The extension loads server configurations from VS Code settings, establishes bidirectional communication channels, monitors connection health, and handles reconnection logic when servers become unavailable. Supports both stdio-based process communication and HTTP-based SSE streaming for remote servers.

Registers a custom chat participant (@mcp) with GitHub Copilot Chat that acts as a proxy to expose all tools and resources from connected MCP servers. The ChatHandler component intercepts chat requests, translates them into MCP tool calls, executes them against the appropriate server, and streams results back to Copilot's chat interface. Uses Copilot's native chat participant API to make MCP tools appear as first-class capabilities within the chat UI.

Handles the full lifecycle of tool invocation: translating Copilot's tool call requests into MCP protocol messages, executing them against the appropriate server, aggregating streaming results (if supported), and returning formatted results back to Copilot Chat. Includes error handling that catches server errors, network failures, and malformed responses, and surfaces them as user-friendly error messages in the chat. Supports both synchronous tool calls (wait for complete result) and asynchronous streaming (return results as they arrive).

Automatically discovers tool schemas from connected MCP servers, converts them to Copilot's LM Tools format (JSON schema with descriptions, parameters, etc.), and registers them with Copilot Chat. When servers connect/disconnect, the tool schemas are dynamically updated, ensuring Copilot always has an accurate view of available tools. The extension handles schema translation between MCP's tool format and Copilot's expected format, including parameter mapping and description extraction.

Provides a set of pre-built MCP tools (fileReadTool, fileEditTool, findFilesTool, listDirectoryTreeTool, runInTerminalTool) that enable Copilot to read, modify, and search files, and execute terminal commands within the VSCode workspace. These tools are implemented as MCP-compatible functions that map directly to VSCode APIs and shell execution, allowing Copilot to perform code editing and system operations without user intervention.

Provides a webview-based UI (ServerViewProvider) for discovering, adding, configuring, and removing MCP servers. The UI displays all configured servers with their connection status, allows users to add new servers by specifying command/args or SSE endpoints, and persists configurations to VSCode settings. Includes a server discovery mechanism that can list available MCP servers from a registry or local npm packages.

Implements a 'listResources' command that queries all connected MCP servers for their available resources (files, documentation, knowledge bases, etc.), aggregates them, and injects them into the Copilot Chat context. Resources are displayed in a structured format within the chat, allowing Copilot to reference them when generating responses. This enables MCP servers to provide domain-specific context (e.g., API documentation, code examples) that Copilot can use to improve answer quality.

Maintains a unified registry of all tools from all connected MCP servers, handling name conflicts and deduplication when multiple servers expose tools with the same name. When a tool is invoked via Copilot Chat, the registry routes the request to the appropriate server based on tool metadata and execution context. The registry is dynamically updated as servers connect/disconnect, ensuring Copilot always has an accurate view of available tools.

Provides a WebSocket polyfill (websocket-polyfill.ts) that enables MCP client libraries designed for Node.js to run within VSCode's extension host environment, which does not natively support WebSocket APIs. The polyfill bridges the gap between Node.js-style WebSocket usage and VSCode's extension APIs, allowing standard MCP client code to work without modification. This is critical for supporting SSE-based MCP servers that require WebSocket-like bidirectional communication.

Continuously monitors the health and connection state of all MCP servers, tracking whether each server is connected, disconnected, or in an error state. The extension displays server status in the VSCode activity bar and sidebar, updates the status in real-time as connections change, and provides diagnostic information (error messages, reconnection attempts) when servers fail. Uses event-driven architecture to propagate connection state changes throughout the extension.

Implements automatic reconnection logic for MCP servers that become unavailable, using exponential backoff to avoid overwhelming the server with reconnection attempts. When a server connection fails, the extension waits before attempting to reconnect, with the wait time increasing exponentially (e.g., 1s, 2s, 4s, 8s) up to a maximum threshold. Reconnection is transparent to the user — tools remain unavailable until the server reconnects, but no manual intervention is required.

Stores all MCP server configurations in VSCode's settings.json file using a structured JSON schema, enabling users to configure servers via VSCode's settings UI or by directly editing JSON. The extension validates configurations against a schema before loading them, catching errors like missing required fields or invalid server types. Configurations are persisted across VSCode sessions and can be version-controlled as part of the workspace configuration.