SignWren API for developers
Create envelopes from your own code, send them for signature, follow their status and download the sealed PDF.
Status. The SignWren API is opening in stages and may not be on your account yet. If Settings shows an API keys section, you can make sandbox keys now; live keys come with the Pro and Business plans. SignWren is an electronic signature app for small businesses; it is not a law firm and does not give legal advice.
What can the SignWren API do?
The SignWren API lets your code do what a sender does in the SignWren app: upload a PDF or Word file, add recipients and signature fields, send the envelope, see who has viewed and signed it, and download the sealed PDF and the certificate of completion when everyone is done. It can also start an envelope from one of your account templates, so a CRM or HR system only has to fill in names and a few values.
It is a JSON REST API under /v1 with Bearer keys, idempotency keys, webhooks signed with HMAC-SHA256 and a free sandbox. It calls the same service layer as the web app, so the same rules apply: plan limits, the excluded-document warning, the signer's consent step and the audit trail.
Where do I start?
Start with the quick start, which sends a sandbox envelope in four requests, then read the page on keys.
- Send your first envelope
Upload a PDF, add a signer and send it, with curl or the Node SDK.
- Keys and authentication
Sandbox and live keys, scopes, rotation, and what a key can see.
- Sandbox and mock server
Test the whole flow with watermarked documents, or offline with the mock server.
- Errors, retries and limits
One error shape, idempotency keys, retries, rate limits and pagination.
- Webhooks and signatures
Get told when an envelope changes, and check that the message came from SignWren.
- Embedded signing
Let a signer sign inside your own app, in a frame or by redirect.
- Node SDK
A typed client with retries, pagination and webhook checks built in.
- Python SDK
The same client for Python, with no dependencies beyond the standard library.
- MCP server for AI assistants
Let an AI assistant send templates and track them, with your approval each time.
- API reference
Every endpoint and schema, generated from the OpenAPI file at build time.
- Changelog
Every change to /v1, dated, and whether you need to do anything.
What can't the API do?
The API can't sign for anyone. There is no endpoint that signs, uploads a ready-made signature for a recipient or ticks the consent box; each signer signs in the signing ceremony, in their own browser or in a frame inside your app. Apart from the connectors listed on the features page, anything that talks to SignWren does it through this API and its webhooks.
What do developers ask most?
Does the sandbox cost anything?
The plan is that every account, Free included, gets sandbox keys for testing, and that the Pro and Business plans add live keys for real documents. Sandbox envelopes are watermarked, are not valid signatures and do not count toward plan usage.
Which languages have an SDK?
There are SDKs for Node.js and Python. Neither is on npm or PyPI yet; email us for the package files. Any language that can make HTTPS requests can use the API directly, and the OpenAPI file works with most client generators.
Can an AI assistant sign a document through the MCP server?
No. The MCP server can create drafts from templates, send them after you approve, remind, void and report status. There is no tool, and no API endpoint, that signs, adopts a signature or gives consent for anyone. Every signature is made by the signer in the signing ceremony.
Where is the OpenAPI file?
The API serves it at https://app.signwren.com/api/v1/openapi.json without a key, and the API reference on this site is generated from the same file each time the site is built.
Last checked against the API spec on .