API documentation

Send any PDF for signing with a single POST. The letssign.now API reference, errors, recipes, support.

The whole signing flow — anchors, signers, dispatch, signed PDF, audit trail, webhooks — sits behind one Bearer-API-key authed endpoint at https://api.wesign.now/v1/*. No templates required, no portal redirect for the recipient, no SDK to install. Three real-life calls ship 90% of integrations.

https://api.letssign.now/v1 is a permanent alias of the same API. The Base URL section says exactly what is — and what isn't — the contract.

Three steps to ship

Mint an API key

Go to Developers → API keys in your workspace and click Create API key. Copy the wsk_live_… token — we only display the plaintext once. Keys minted before the September 2026 rename start with lsk_live_ and keep working unchanged.

Send your first signing request

Replace YOUR_KEY and run this in a terminal:

curl -X POST https://api.wesign.now/v1/signing-requests \
  -H "Authorization: Bearer YOUR_KEY" \
  -F "file=@contract.pdf" \
  -F 'signers=[{"email":"signer@example.com","role":"signer"}]'

Drop [[ls:signature:signer]] anywhere in your PDF and we place a signature field there. No marker? We auto-append a signature page. Need the signer to confirm an SMS code before they can sign? Add phone_e164 and require_sms_verification to the signer — see Second factor by SMS.

(Optional) Receive real-time events

Register an outbound webhook at Developers → Webhooks (or pass callback_url per-request). We POST signing_request.signed as each signer completes, and document.completed with a key-authenticated signed-PDF URL when everyone's done. Every delivery is HMAC-signed (X-WeSign-Signature) — verify it before trusting the body.