Converting MCP Servers to Skills

Letta Code is not itself an MCP client, but as a general computer-use agent, you can easily connect to any MCP server using the scripts in this skill.

What is MCP?

MCP (Model Context Protocol) is a standard for exposing tools to AI agents. MCP servers provide tools via JSON-RPC, either over:

• HTTP - Server running at a URL (e.g., http://localhost:3001/mcp)
• stdio - Server runs as a subprocess, communicating via stdin/stdout

Quick Start: Connecting to an MCP Server

Step 1: Determine the transport type

Ask the user:

• Is it an HTTP server (has a URL)?
• Is it a stdio server (runs via command like npx, node, python)?

Step 2: Test the connection

For HTTP servers:

npx tsx <SKILL_DIR>/scripts/mcp-http.ts <url> list-tools

# With auth header
npx tsx <SKILL_DIR>/scripts/mcp-http.ts <url> --header "Authorization: Bearer KEY" list-tools

Where <SKILL_DIR> is the Skill Directory shown when the skill was loaded (visible in the injection header).

For stdio servers:

npx tsx <SKILL_DIR>/scripts/mcp-stdio.ts "<command>" list-tools

# Examples
npx tsx <SKILL_DIR>/scripts/mcp-stdio.ts "npx -y @modelcontextprotocol/server-filesystem ." list-tools
npx tsx <SKILL_DIR>/scripts/mcp-stdio.ts "python server.py" list-tools

Step 3: Explore available tools

# List all tools
... list-tools

# Get schema for a specific tool
... info <tool-name>

# Test calling a tool
... call <tool-name> '{"arg": "value"}'

Creating a Dedicated Skill

When an MCP server will be used repeatedly, create a dedicated skill for it. This makes future use easier and documents the server's capabilities.

Decision: Simple vs Rich Skill

Simple skill (just SKILL.md):

• Good for straightforward servers
• Documents how to use the parent skill's scripts with this specific server
• No additional scripts needed

Rich skill (SKILL.md + scripts/):

• Good for frequently-used servers
• Includes convenience wrapper scripts with defaults baked in
• Provides a simpler interface than the generic scripts

See references/skill-templates.md for templates.

Built-in Scripts Reference

mcp-http.ts - HTTP Transport

Connects to MCP servers over HTTP. No dependencies required.

npx tsx mcp-http.ts <url> [options] <command> [args]

Commands:
  list-tools              List available tools
  list-resources          List available resources
  info <tool>             Show tool schema
  call <tool> '<json>'    Call a tool
  login                   Run OAuth flow and cache tokens for this server
  logout                  Clear cached OAuth tokens for this server

Options:
  --header "K: V"         Add HTTP header (repeatable). Disables auto-OAuth.
  --auth <mode>           "auto" (default), "oauth", or "none"
  --timeout <ms>          Request timeout (default: 30000)

Examples:

# Basic usage
npx tsx mcp-http.ts http://localhost:3001/mcp list-tools

# With static bearer authentication
npx tsx mcp-http.ts http://localhost:3001/mcp --header "Authorization: Bearer KEY" list-tools

# OAuth-protected server (opens a browser to sign in, then caches tokens)
npx tsx mcp-http.ts https://example.com/mcp login
npx tsx mcp-http.ts https://example.com/mcp list-tools

# Call a tool
npx tsx mcp-http.ts http://localhost:3001/mcp call vault '{"action":"search","query":"notes"}'

OAuth support: When a server returns 401 WWW-Authenticate: Bearer ... and no static Authorization header was supplied, mcp-http.ts will automatically:

1. Discover the authorization server via resource_metadata, the realm= param, or the server's own origin (.well-known/oauth-authorization-server then .well-known/openid-configuration).
2. Dynamically register a public client with PKCE (token_endpoint_auth_method: none).
3. Open the system browser to the authorization endpoint, catch the redirect on a 127.0.0.1 loopback port, and exchange the code for tokens.
4. Cache the token set (and the registered client) at ~/.letta/mcp-oauth/<host>_<path>.json with 0600 perms.
5. Auto-refresh expired access tokens using the stored refresh token before each request; if refresh fails, it re-runs the browser flow once.

Use login to run the flow explicitly (e.g. as a first step in a skill's setup) and logout to clear cached tokens. Passing an explicit --header "Authorization: ..." disables auto-OAuth so you stay in control. Pass --auth none to force static-only behavior.

mcp-stdio.ts - stdio Transport

Connects to MCP servers that run as subprocesses. No dependencies required.

npx tsx mcp-stdio.ts "<command>" [options] <action> [args]

Actions:
  list-tools              List available tools
  list-resources          List available resources
  info <tool>             Show tool schema
  call <tool> '<json>'    Call a tool

Options:
  --env "KEY=VALUE"       Set environment variable (repeatable)
  --cwd <path>            Set working directory
  --timeout <ms>          Request timeout (default: 30000)

Examples:

# Filesystem server
npx tsx mcp-stdio.ts "npx -y @modelcontextprotocol/server-filesystem ." list-tools

# With environment variable
npx tsx mcp-stdio.ts "node server.js" --env "API_KEY=xxx" list-tools

# Call a tool
npx tsx mcp-stdio.ts "python server.py" call read_file '{"path":"./README.md"}'

Common MCP Servers

Here are some well-known MCP servers:

Troubleshooting

"Cannot connect" error:

• For HTTP: Check the URL is correct and server is running
• For stdio: Check the command works when run directly in terminal

"Authentication required" error:

• Add --header "Authorization: Bearer YOUR_KEY" for HTTP servers using static bearers
• Or --env "API_KEY=xxx" for stdio servers that need env vars
• For OAuth-protected HTTP servers, just run any command (or login) — the helper will do PKCE + dynamic client registration and cache tokens under ~/.letta/mcp-oauth/. Delete that file (or run logout) to force a re-login.

OAuth issues:

• "Could not discover OAuth server metadata": the server didn't include resource_metadata and its origin doesn't serve .well-known/oauth-authorization-server or .well-known/openid-configuration. Fall back to a static bearer, or point the helper at the auth server manually via a custom skill.
• "Dynamic client registration failed": the auth server disables open DCR. You'll need to pre-register a client and pass its client_id (and any required credentials) via headers, or wrap this skill with a server-specific one.
• "state mismatch" / callback timeout: another process may be holding the browser callback; re-run and complete the sign-in in the newly opened tab.

Tool call fails:

• Use info <tool> to see the expected input schema
• Ensure JSON arguments match the schema