eSignature API: Add Document Signing to Your App

The short answer: the OpenSign™ eSignature API lets you embed document signing into your own application — create documents from templates, send signature requests, check status and receive webhook events when documents are signed. It's free, open source, and self-hostable, so you're never locked into a vendor.

What you can build

• Automated onboarding — send NDAs, contracts or agreements the moment a user signs up.
• In-app signing — let users sign documents without leaving your product.
• Workflow automation — trigger signature requests from your CRM, HRIS or backend.
• Bulk sending — generate many documents from one template programmatically.

Core API capabilities

• Create and manage templates and documents.
• Send signature requests to one or more signers.
• Track status and retrieve completed files and certificates.
• Receive webhooks for events like viewed, signed and completed.
• Manage contacts and signing order.

Full reference and authentication details are in the OpenSign API documentation.

Example workflow

1. Authenticate with your API token.
2. Create a document from a saved template.
3. Add signers and field positions in the request body.
4. Send the signature request — signers receive a secure link.
5. Listen for the completed webhook, then fetch the signed PDF.

Why developers choose OpenSign

• Free to start, with no per-signature pricing surprises.
• Open source — read the code and contribute.
• Self-hostable — run the API inside your own infrastructure for full data control. See the self-hosting guide.
• Standards-based — legally binding signatures with audit trails.

Not a developer? You can do everything through the OpenSign app instead.