Physical Mail API for LLMs

An MCP-first physical-mail API designed to be discoverable, callable, and well-typed for large language models. Tool surface, agent-readable docs, and pricing.

apillmreference

· Updated

Designed for the model, not the dev portal

Most APIs are designed for humans reading docs. Mailsnail is designed for an LLM reading documentation cold and figuring out how to call it. Concretely:

  • /llms.txt and /llms-full.txt at the root, with crisp tool descriptions.
  • /openapi.json with rich descriptions and an x-mcp extension pointing back at the MCP server.
  • /setup has ready-to-paste setup for every major client. The hosted server is one URL with OAuth sign-in the client handles itself.
  • JSON-LD SoftwareApplication and WebAPI graphs on the homepage.

Tool surface

  • verify_address (address fields). Free.
  • preview_letter (letter fields) — proof + price, no charge. Managed mode.
  • send_letter (recipient, body, optional return address, optional subject).
  • get_letter (receipt_token): status, plus USPS tracking for certified mail.
  • cancel_letter (receipt_token): cancel before printing, refunded to your balance.

Primitives only. No 17-knob configurations. The schemas are tight enough that an agent can call them on the first try without reading more docs.

Why this matters

If an agent has to read 8 pages of docs to figure out an API, it won't. If the surface is small, well-typed, and self-describing, it will. We optimize aggressively for the second case.

Wire Mailsnail into your agent

Add one URL and sign in. Nothing to install and no API key. In Claude Code:

Claude Code
claude mcp add -t http mailsnail https://api.mailsnail.dev/mcp

Then run /mcp and choose Authenticate. In Claude Desktop or ChatGPT, add https://api.mailsnail.dev/mcp as a custom connector. Cursor and other JSON-config clients take:

mcp.json
{
  "mcpServers": {
    "mailsnail": {
      "url": "https://api.mailsnail.dev/mcp"
    }
  }
}

A one-page letter is from $1.21, and preview_letter shows the proof and exact price before anything is charged. Setup for every app →

See also

MCP Server for Direct Mail

Mailsnail is the Model Context Protocol server that lets any MCP agent send physical letters and certified mail. Connection details, tool list, and pricing.

Click2Mail API Alternative

Looking at Click2Mail for programmatic mail? Mailsnail is the same idea built for AI agents: MCP-first, with agent-readable docs and a simple HTTP fallback.