Add E-Signatures to Express.js

Quick start

1. Get an API key from signb.ee (free, no credit card)
2. Set SIGNBEE_API_KEY in your environment
3. Add the code below to your app

Express.js example

const express = require("express");
const app = express();
app.use(express.json());

app.post("/send-contract", async (req, res) => {
  const response = await fetch("https://signb.ee/api/send", {
    method: "POST",
    headers: {
      Authorization: `Bearer ${process.env.SIGNBEE_API_KEY}`,
      "Content-Type": "application/json",
    },
    body: JSON.stringify(req.body),
  });
  res.json(await response.json());
});

app.listen(3000);

What happens

1. Your app sends markdown or a PDF URL to Signbee
2. Signbee generates a PDF (if markdown) and emails the recipient a signing link
3. Recipient signs — both parties receive the signed PDF with SHA-256 certificate

Also works with AI agents

Install the MCP server to let Claude, Cursor, or Windsurf send documents directly:

npx -y signbee-mcp

Integration details

Express.js is the most widely used Node.js web framework with over 30 million weekly npm downloads. Adding e-signatures to Express requires just a single route handler — no middleware, no SDK, no additional dependencies.

Middleware considerations: For production Express apps, add authentication middleware to protect your contract-sending endpoint. Use express-rate-limit to prevent abuse, and helmet for security headers. The Signbee API has its own rate limiting, but protecting your endpoint reduces unnecessary API calls.

Request validation: Validate incoming requests before forwarding to Signbee. Check that content, senderName, senderEmail, recipientName, and recipientEmail are present and correctly formatted. Use express-validator or Joi for structured validation.

Async error handling: The example uses async/await. In Express 4, unhandled promise rejections don't trigger error middleware automatically. Wrap handlers in a try/catch or use express-async-errors. Express 5 handles this natively.

Webhook integration: For tracking signing status, set up a webhook endpoint in your Express app to receive Signbee callbacks when documents are signed. This lets you update your database, trigger follow-up emails, or advance workflow states automatically.

FAQs