GitHub Webhook Testing

1. Local app setup

Create a local webhook endpoint at: /webhooks/github

import express from 'express'
import crypto from 'crypto'

const app = express()
app.post('/webhooks/github', express.raw({ type: 'application/json' }), (req, res) => {
  const signature = req.header('x-hub-signature-256') || ''
  const rawBody = req.body as Buffer
  const expected = 'sha256=' + crypto
    .createHmac('sha256', process.env.GITHUB_WEBHOOK_SECRET!)
    .update(rawBody)
    .digest('hex')

  const signatureBuf = Buffer.from(signature)
  const expectedBuf = Buffer.from(expected)
  const valid =
    signatureBuf.length === expectedBuf.length &&
    crypto.timingSafeEqual(signatureBuf, expectedBuf)

  if (!valid) {
    return res.status(401).send('invalid signature')
  }

  console.log('github event:', req.header('x-github-event'))
  res.status(200).send('ok')
})

app.listen(3000, () => console.log('listening on :3000'))

2. Run InstaTunnel command

instatunnel 3000 --subdomain github-hooks

Keep a fixed subdomain so your provider dashboard URL does not keep changing.

3. Provider config fields to paste

Use the helper below to generate exact values with your chosen subdomain and path.

4. Send test event

1. In repository settings, open the webhook and click "Redeliver" on a recent delivery.
2. Or click "Test delivery" after saving webhook settings.
3. Check your app logs for event type and successful signature check.

5. Verify signature

Verify this header on every request: x-hub-signature-256

const expected = 'sha256=' + crypto
  .createHmac('sha256', process.env.GITHUB_WEBHOOK_SECRET!)
  .update(rawPayloadBuffer)
  .digest('hex')

const valid = Buffer.from(signature).length === Buffer.from(expected).length &&
  crypto.timingSafeEqual(Buffer.from(signature), Buffer.from(expected))
if (!valid) return res.status(401).send('invalid signature')

6. Retries and idempotency

• Use GitHub delivery ID as your idempotency key.
• Persist processed delivery IDs for a safe replay window.
• Handle out-of-order events by reading current resource state before mutating.

7. Common failures and quick fixes