Test Resend webhooks without deploying

Capture email delivered, bounced and complained events from Resend, which signs through Svix like Clerk does.

Get a URL that accepts the webhook#

A capture URL takes any method, any body, and records exactly what arrived: method, headers, query string, body and source IP. You do not need an account to make one, and an anonymous URL is deleted after 24 hours.

bash·No signup required

curl -X POST https://mocklane.com/api/v1/anon/endpoints \
  -H "Content-Type: application/json" -d '{}'

# The response carries a capture URL of the form:
#   https://mocklane.com/h/<endpoint-id>

Paste that URL into Resend at Resend dashboard, Webhooks, Add Webhook, then trigger something. Events worth starting with:

email.sent
email.delivered
email.bounced
email.complained

Verify the svix-signature header#

Resend signs each request so you can tell a real delivery from anyone who has guessed your URL. The digest is HMAC-SHA256 over the message id, the timestamp and the raw body, joined with full stops, base64-encoded, keyed with your signing secret (starts with whsec_).

Header: svix-signature
Timestamp header: svix-timestamp
Value format: v1,g0hM9SsE+OTPJTGt/tmIKtSyZlE3uFJELVlNIOLJ1OE=
Algorithm: HMAC-SHA256, base64
Signed content: the message id, the timestamp and the raw body, joined with full stops

javascript·Verify in Node

const crypto = require("crypto");

// Svix signs "{id}.{timestamp}.{rawBody}".
const signed = `${req.headers["svix-id"]}.${req.headers["svix-timestamp"]}.${rawBody}`;

// The key is the DECODED secret, not the whsec_ string itself.
const key = Buffer.from(process.env.RESEND_WEBHOOK_SECRET.replace(/^whsec_/, ""), "base64");
const expected = crypto.createHmac("sha256", key).update(signed).digest("base64");

// svix-signature can carry several space-separated "v1,<sig>" values during
// a secret rotation. Any one of them matching is a pass.
const ok = req.headers["svix-signature"]
  .split(" ")
  .some((part) => {
    const sig = part.split(",")[1];
    return sig && crypto.timingSafeEqual(Buffer.from(expected), Buffer.from(sig));
  });

Compare digests with a constant-time function such as crypto.timingSafeEqual. A plain === returns as soon as two bytes differ, and that timing difference is enough to recover a valid signature one byte at a time.

What catches people out#

The signing secret is prefixed with whsec_. The key is the base64 decode of everything after that prefix, not the literal string, which is the step most hand-written Svix verifiers miss.
The scheme is identical to Clerk's, because both deliver through Svix. A verifier written for one works for the other.
email.bounced is the event worth wiring first. A bounce you never process becomes a suppressed address and a quietly failing signup flow.

Replay it until your handler is right#

A captured request can be re-sent to your own endpoint, with the body or headers edited first. That turns a bug that needed a real Resend event into something you can reproduce on demand, which matters most for events that are awkward to trigger twice.

Assert on it in CI#

A scenario chains the steps into one run that passes or fails, so a change that breaks your Resend handling fails the build rather than reaching production.

yaml·scenario.yaml

steps:
  - type: send_webhook
    body: { event: "email.sent" }

  - type: wait_for_webhook
    timeout_seconds: 30
    assert:
      - status_code equals 200

Triggered from CI with an API token. See the scenarios documentation for the full step list.

Everything above is on the free plan, and the capture URL works before you sign up. Create a free account to keep a URL for longer than 24 hours.

Signature details checked against Resend’s documentation on 22 October 2026. Schemes change: if this page and their docs disagree, believe theirs and tell us.