tally-webhooks

Tally Webhooks

When to Use This Skill

• How do I receive Tally webhooks?
• How do I verify Tally webhook signatures (the Tally-Signature header)?
• How do I handle FORM_RESPONSE form submission events?
• How do I read form answers from data.fields?
• Why is my Tally webhook signature verification failing?

Verification (core)

Tally signs webhooks with an optional signing secret. When a secret is set on the webhook, each request carries a Tally-Signature header (case-insensitive) whose value is base64(HMAC-SHA256(signingSecret, rawJsonBody)). There is no timestamp scheme and it is not the Standard Webhooks spec. Always HMAC the raw request body — re-serializing the parsed JSON can change bytes/key order and break the comparison.

If no signing secret is configured, Tally sends requests unsigned, so your handler must decide what to do when the header is absent. Recommended: set a signing secret and reject unsigned/invalid requests; only skip verification when you have intentionally left the secret unset.

Node:

const crypto = require('crypto');

function verifyTallyWebhook(rawBody, signatureHeader, signingSecret) {
  if (!signatureHeader) return false;
  const expected = crypto.createHmac('sha256', signingSecret).update(rawBody).digest('base64');
  try {
    return crypto.timingSafeEqual(Buffer.from(signatureHeader), Buffer.from(expected));
  } catch {
    return false; // length mismatch = invalid
  }
}

Python:

import hmac, hashlib, base64

def verify_tally_webhook(raw_body: bytes, signature_header: str, signing_secret: str) -> bool:
    if not signature_header:
        return False
    expected = base64.b64encode(
        hmac.new(signing_secret.encode(), raw_body, hashlib.sha256).digest()
    ).decode()
    return hmac.compare_digest(signature_header, expected)

Important: Tally webhooks are free on all plans. Your endpoint must return a 2XX status within a 10-second timeout. Failed deliveries retry after 5m → 30m → 1h → 6h → 1d. Do slow work asynchronously.