Introduction
Build on LettrLabs — send direct mail programmatically, track attributions and conversions, and react to events in real time.
The LettrLabs API lets you drive real, physical direct mail from your own systems: create orders from a template, target recipients, track delivery and conversions, and receive events as they happen. Everything the LettrLabs app does for direct‑mail automation is available over a simple HTTPS + JSON API.
Building with an AI agent? Point it at /llms.txt for a
curated index of these docs, or /llms-full.txt for the
full content as a single file — so it can build against the LettrLabs API
effectively.
What you can do
- Create orders from a template and a recipient list — handwritten cards and printed mail, sent on your schedule (see Creating an Order).
- Attribute and convert — record conversions against the mail you send and read them back for reporting (see Attributions & Conversions).
- Manage your address book and recipients — add entries and adjust an order's recipients before it mails.
- React to events — receive inbound webhooks when something happens, with optional HMAC signature verification (see Inbound webhooks).
Base URL
All requests go to:
https://app.lettrlabs.com/apiEvery endpoint is documented under API Reference, grouped by area, with parameters, request and response schemas, status codes, and an interactive “try it” console you can call with your own key.
Authentication in one line
Every request carries your public API key in the X-API-KEY header:
curl https://app.lettrlabs.com/api/v1/me \
-H "X-API-KEY: your_api_key_here"You generate that key inside the LettrLabs app — the full walk‑through is in Authentication & API keys.
Next steps
- Generate an API key and make your first
authenticated call to
GET /v1/me. - Follow the order of operations to send your first order end to end.
- Not sure whether to drive orders yourself or let the app? See Automations vs. creating an order.
- Explore the full API Reference and try requests live.