Using MCP

Using MCP Skill

Discovers, configures, and verifies Model Context Protocol servers from Copilot, Claude Code, Cursor, and other MCP-compliant clients. Treats mcp/registry.yaml as the source of truth and least-privilege scopes as non-negotiable. Does NOT itself author servers (see building-mcp-servers) or bypass the broker (see calling-mcp-tools-via-subprocess).

When to Use

• User mentions MCP, MCP server, "add a tool", "connect to ".
• Agent needs data from an external system (GitHub, Postgres, Azure, Graph, browser, FS).
• "Why can't Copilot see X?" — check the MCP wiring before anything else.
• Authoring or modifying .vscode/mcp.json, .mcp.json, .cursor/mcp.json.

Prerequisites

• A Copilot client that supports MCP (Copilot CLI, VS Code agent mode, Claude Code, Cursor).
• mcp/registry.yaml accessible in the dojo (this skill is parasitic on the registry).
• npx / node available for stdio servers, or hosted endpoint for Streamable HTTP.
• Auth context already set up (az login, gh auth, OAuth flow, etc.) — never paste raw secrets into configs.
• The view, edit, and powershell Copilot tools.

How to Run

1. Open `mcp/registry.yaml`. Find the server.
2. Pick the transport (stdio for local, Streamable HTTP for hosted).
3. Drop the config snippet from `mcp/configs/` into the client's config file.
4. Set scopes to least privilege.
5. Verify the server is green in the client; call one tool end-to-end.

Quick Reference

Procedure

Step 1: Registry First

Use view on mcp/registry.yaml. If the server is listed, use its sanctioned config. If it is not listed, hand off to building-mcp-servers first and add a registry entry before consuming it.

Step 2: Pick Transport

Use the transport table above. Default to stdio for dev; Streamable HTTP for anything shared.

Step 3: Configure

Use edit to add the snippet to the client's config file. Reference env vars (${env:VAR}) — never inline secrets. Pin server version (@x.y.z) for reproducibility.

// .vscode/mcp.json
{
  "servers": {
    "github": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-github@1.4.0"],
      "env": { "GITHUB_PERSONAL_ACCESS_TOKEN": "${env:GH_PAT}" }
    }
  }
}

Step 4: Scope Down

Apply the scope table. Default to read-only unless the workflow demonstrably requires writes. Document the scope in the registry entry, not just the config.

Step 5: Verify

Run via the powershell tool:

VS Code        → "MCP: Show Installed Servers" command, confirm green status
Claude Code    → claude mcp list
Copilot CLI    → /mcp list
Generic        → node mcp/scripts/mcp-subprocess.js list <server-binary>

Then ask the agent to perform a tiny task that exercises one tool. Failure modes to check:

• Trailing commas in JSON.
• Wrong type (stdio vs http).
• Server printed to stdout before the JSON-RPC handshake (kills framing).
• Missing env var the server silently needs.

Step 6: Fallback When the Broker Misbehaves

If tools/call hangs or "tools_changed" loops, do not reconfigure — bypass. Switch to calling-mcp-tools-via-subprocess.

Pitfalls

• DO NOT paste an MCP URL into chat instead of a config file.
• DO NOT use a repo-scope classic GitHub token. Fine-grained, scoped.
• DO NOT allow-list / or ~ for the filesystem MCP server.
• DO NOT hard-code tokens into committed configs. Use ${env:VAR}.
• DO NOT add a server without verifying the agent can actually invoke it.
• DO NOT re-implement GitHub / Postgres / FS access as a custom skill when an MCP server already exists.

Verification

• Server entry exists in mcp/registry.yaml (with scopes documented).
• Config file uses the snippet from mcp/configs/ verbatim (except env / scopes).
• Server pinned to a specific version (no floating latest).
• Client shows the server as connected / green.
• One representative tool call executed end-to-end via the agent.
• No secrets in committed files (grep for token patterns).