Webhooks

Webhooks allow your application to receive real-time notifications when events occur in API Sign. Instead of repeatedly polling our API, webhooks push event data to your application immediately when something happens.

Every endpoint on this page is authenticated with your API key in the x-api-key header, and every one of them takes and returns JSON.

Webhook Endpoints

Available Events

Event names use underscores. Any other spelling is rejected by /webhook/create and /webhook/update with a 400.

That is the complete list. There are no template events.

Webhook Payload

Every delivery is a POST with this body:

{
  "id": "clx8k2q1b0002qz3f6j0e3c8f",
  "event": "contract_signed",
  "created_at": "2026-07-28T14:30:00.000Z",
  "data": {
    "organization_id": "clx8k1m4z0000qz3f7g2c1a9d",
    "contract": {
      "id": "clx8k2n7b0003qz3f8j4e3c1f",
      "name": "Service Agreement",
      "status": "sent",
      "sent_at": "2026-07-28T14:02:11.000Z",
      "test_mode": false
    },
    "signer": {
      "id": "clx8k2o9c0004qz3f1k5f4d2g",
      "name": "Jordan Lee",
      "email": "jordan@acme.com",
      "status": "signed",
      "signed_at": "2026-07-28T14:30:00.000Z"
    },
    "metadata": {}
  }
}

Webhook Headers

Every delivery carries these headers, plus any custom headers you set on the webhook:

The event type is not in a header. Read it from event in the body.

Signature Verification

X-Webhook-Signature has the form t=1753712345,v1=9f86d081.... To verify:

1. Split the header on , and read t= and v1=.
2. Reject the request if t is more than 5 minutes from now.
3. Compute HMAC-SHA256(key = your webhook secret, message = "<t>.<raw body>") and hex-encode it.
4. Compare that to v1 with a constant-time comparison.

The key is the whsec_... secret exactly as returned by /webhook/create, used as a UTF-8 string.

Node.js Example

const crypto = require('crypto');

function verifyWebhookSignature(rawBody, signatureHeader, secret) {
  // Header format: t=<unix seconds>,v1=<hex hmac>
  const parts = Object.fromEntries(
    signatureHeader.split(',').map((p) => {
      const i = p.indexOf('=');
      return [p.slice(0, i), p.slice(i + 1)];
    })
  );

  const timestamp = parts.t;
  const received = parts.v1;
  if (!timestamp || !received) return false;

  // Reject replays older than 5 minutes
  if (Math.abs(Date.now() / 1000 - parseInt(timestamp, 10)) > 300) return false;

  const expected = crypto
    .createHmac('sha256', secret)
    .update(`${timestamp}.${rawBody}`, 'utf8')
    .digest('hex');

  // timingSafeEqual throws on length mismatch, so check length first
  if (received.length !== expected.length) return false;
  return crypto.timingSafeEqual(Buffer.from(received), Buffer.from(expected));
}

// Usage in Express.js — note express.raw, so rawBody is the exact bytes we signed
app.post('/webhooks/apisign', express.raw({ type: 'application/json' }), (req, res) => {
  const rawBody = req.body.toString('utf8');

  if (!verifyWebhookSignature(rawBody, req.get('X-Webhook-Signature'), process.env.APISIGN_WEBHOOK_SECRET)) {
    return res.status(401).send('Invalid signature');
  }

  const event = JSON.parse(rawBody);

  switch (event.event) {
    case 'contract_signed':
      // one signer finished
      break;
    case 'contract_completed':
      // everyone finished; contract.status is now "signed"
      break;
  }

  res.status(200).send('OK');
});

Python Example

import hmac
import hashlib
import time


def verify_webhook_signature(raw_body: str, signature_header: str, secret: str) -> bool:
    # Header format: t=<unix seconds>,v1=<hex hmac>
    parts = dict(p.split("=", 1) for p in signature_header.split(","))
    timestamp = parts.get("t")
    received = parts.get("v1")
    if not timestamp or not received:
        return False

    # Reject replays older than 5 minutes
    if abs(time.time() - int(timestamp)) > 300:
        return False

    expected = hmac.new(
        secret.encode("utf-8"),
        f"{timestamp}.{raw_body}".encode("utf-8"),
        hashlib.sha256,
    ).hexdigest()

    return hmac.compare_digest(received, expected)

Delivery and Retries

A delivery is attempted as soon as the event is recorded. A delivery counts as failed if the response status is not 2xx, the connection cannot be established, the TLS handshake fails, or the request does not complete within 30 seconds.

Each delivery gets up to 5 attempts. The backoff after each failed attempt is:

A failure counter runs across deliveries, incrementing on every failed attempt and resetting to 0 on the first success. When it reaches 10, the webhook's status becomes failed and it stops receiving events entirely — so two fully exhausted deliveries are enough to disable an endpoint. Set status back to active with /webhook/update to re-enable it; that also resets the counter.

Best Practices

Respond Quickly

Return a 2xx response immediately, then process the event asynchronously:

app.post('/webhooks/apisign', express.raw({ type: 'application/json' }), (req, res) => {
  const rawBody = req.body.toString('utf8');
  if (!verifyWebhookSignature(rawBody, req.get('X-Webhook-Signature'), secret)) {
    return res.status(401).send('Invalid signature');
  }

  webhookQueue.add('process-event', JSON.parse(rawBody));
  res.status(200).send('OK');
});

Handle Duplicates

A retried delivery repeats the same payload, so dedupe on the payload's id:

function handleWebhookEvent(event) {
  if (alreadyProcessed(event.id)) return;
  processEvent(event);
  markProcessed(event.id);
}

Use HTTPS

We do not reject http:// endpoint URLs, but you should not use one. The payload contains signer names and email addresses, and the signature only proves the request came from us — it does not encrypt anything.

Testing Webhooks

Send a test delivery

POST /webhook/test with {"id": "<webhook id>"} sends a synthetic contract_signed delivery to your URL and returns the status code, body, and duration it got back, along with the exact payload and headers it sent. The same thing is available in the dashboard under Account → Webhooks.

Test deliveries differ from real ones in two ways: the payload carries "test": true, and the request carries an extra X-Webhook-Test: true header. They are not recorded in your delivery history.

{
  "id": "test_1753712345678",
  "event": "contract_signed",
  "created_at": "2026-07-28T14:30:00.000Z",
  "test": true,
  "data": {
    "organization_id": "clx8k1m4z0000qz3f7g2c1a9d",
    "contract": { "id": "test_contract_id", "name": "Test Contract", "status": "signed", "test_mode": true },
    "signer": { "id": "test_signer_id", "name": "Test Signer", "email": "test@example.com", "status": "signed" },
    "metadata": { "message": "This is a test webhook delivery" }
  }
}

Local Development

Use ngrok to expose your local server:

ngrok http 3000
# Use the HTTPS URL: https://abc123.ngrok.io/webhooks/apisign