# LettersByLetter

> LettersByLetter is a physical letter mailing API and SaaS. Upload a PDF or compose a letter; we print and mail USPS First-Class letters, Certified Mail, and 4×6 postcards. Pay with card or USDC via x402.

LettersByLetter.com is operated by Rainmaker LLC d/b/a LettersByLetter.com. Office: 7 Elm St 2R, New Haven, CT 06510. Support: hello@lettersbyletter.com.

## Product

- Web app for composing or uploading PDFs and sending physical mail
- REST API (`lbl_live_` / `lbl_test_` Bearer keys)
- MCP server for Claude Desktop, Cursor, and other MCP clients
- x402 payments in USDC on Base and Solana
- Fulfillment via LetterStream into USPS (live mode). Demo mode never purchases postage.

## Pricing

Authoritative list prices in USD. Credits are 1:1 with USD cents. No subscription required.

- First-Class letter: $1.49 first page + $0.25 each additional page
- Certified Mail: $12.99 base piece (first page included) + $0.25 each additional page
- Postcard: $1.99 flat (4×6 color)
- Optional Certified Electronic Return Receipt: $2.40

## Docs

- [Documentation](https://lettersbyletter.com/docs): https://lettersbyletter.com/docs
- [REST API](https://lettersbyletter.com/docs/api): https://lettersbyletter.com/docs/api
- [OpenAPI 3.1](https://lettersbyletter.com/api/v1/openapi.json): https://lettersbyletter.com/api/v1/openapi.json
- [MCP](https://lettersbyletter.com/docs/mcp): https://lettersbyletter.com/docs/mcp
- [x402 + USDC](https://lettersbyletter.com/docs/x402): https://lettersbyletter.com/docs/x402
- [Fonts](https://lettersbyletter.com/docs/fonts): https://lettersbyletter.com/docs/fonts
- [Pricing](https://lettersbyletter.com/pricing): https://lettersbyletter.com/pricing

## Optional

- [Full agent brief](https://lettersbyletter.com/llms-full.txt): https://lettersbyletter.com/llms-full.txt
- [AI plugin descriptor](https://lettersbyletter.com/.well-known/ai-plugin.json): https://lettersbyletter.com/.well-known/ai-plugin.json
- [MCP discovery](https://lettersbyletter.com/.well-known/mcp.json): https://lettersbyletter.com/.well-known/mcp.json
- [Contact](https://lettersbyletter.com/contact): https://lettersbyletter.com/contact
- [Terms of Use](https://lettersbyletter.com/terms): https://lettersbyletter.com/terms
- [Privacy Policy](https://lettersbyletter.com/privacy): https://lettersbyletter.com/privacy