Twilio Webhook Testing

1. Local app setup

Create a local webhook endpoint at: /webhooks/twilio/sms

import express from 'express'
import twilio from 'twilio'

const app = express()
app.use(express.urlencoded({ extended: false }))

app.post('/webhooks/twilio/sms', (req, res) => {
  const signature = req.header('x-twilio-signature') || ''
  const url = process.env.PUBLIC_WEBHOOK_URL!
  const valid = twilio.validateRequest(
    process.env.TWILIO_AUTH_TOKEN!,
    signature,
    url,
    req.body
  )

  if (!valid) return res.status(403).send('invalid signature')

  console.log('sms from:', req.body.From, 'body:', req.body.Body)
  res.type('text/xml').send('<Response></Response>')
})

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

2. Run InstaTunnel command

instatunnel 3000 --subdomain twilio-dev

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. Set your Twilio phone number webhook URL to the tunnel URL.
2. Send an SMS to that Twilio number from your phone.
3. Validate received payload and XML response in local logs.

5. Verify signature

Verify this header on every request: x-twilio-signature

const valid = twilio.validateRequest(
  process.env.TWILIO_AUTH_TOKEN!,
  req.header('x-twilio-signature')!,
  publicWebhookUrl,
  req.body
)
if (!valid) return res.status(403).send('invalid signature')

6. Retries and idempotency

• Use MessageSid/CallSid as idempotency keys.
• Return valid TwiML quickly to prevent repeated retries.
• Log signature validation errors separately from business logic errors.

7. Common failures and quick fixes