Webhook Debugging & Inspection
Inspect, validate, and test webhook payloads with signature verification.
Overview
Debugging webhooks requires inspecting the raw payload, verifying HMAC signatures, and validating the JSON structure against your expected schema. This workflow handles all three without exposing your webhook secrets.
Step-by-Step Implementation
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Quick Summary
Webhook debugging is forensic work: capture the raw payload + headers, pretty-print to spot anomalies, then validate against your expected schema to catch silent field drift. Always verify HMAC signatures before trusting any payload.
Key Takeaways
- Always verify the `X-Hub-Signature` (or provider-equivalent) HMAC, unsigned webhooks are forgeable.
- Webhooks are at-least-once delivery, your handler must be idempotent (use `idempotency_key` or event IDs).
- Return 2xx fast (<5s); do heavy work async. Long handlers cause provider retries and duplicate events.
- Store recent payloads (last 24h) for replay during incident response, providers don't retain them forever.
- Test with provider-specific signing secrets, not just random strings, signature algorithms vary (HMAC-SHA256, JWT, custom).
When to use it
- Debugging a Stripe/GitHub/Shopify webhook that's silently failing in production.
- Onboarding a new webhook integration where the provider's docs are incomplete or out of date.
- Detecting webhook schema drift after a provider releases a new API version.
- Building a local development tunnel (ngrok, Cloudflare Tunnel) to receive webhooks during development.
Common Mistakes
- Trusting the webhook payload without signature verification, anyone can POST to your endpoint.
- Treating webhook delivery as exactly-once, you'll get duplicates; idempotency is mandatory.
- Returning 500 for known issues, most providers retry aggressively, amplifying the problem.
- Logging full payloads to disk, PII / secret leakage. Redact sensitive fields before logging.
Webhook Debugging & Inspection, Frequently Asked
How do I test webhooks locally?
Use ngrok, Cloudflare Tunnel, or `smee.io` to expose your localhost. Most providers have a 'redeliver' button so you can replay captured events.
What if the webhook is missing the signature header?
Reject it. Almost every provider signs webhooks; missing the header is either misconfiguration or attack. Don't 'temporarily' bypass it.
Should webhook handlers be idempotent?
Yes, assume every event will arrive at least twice. Store processed event IDs and return early on duplicates. SQS/Kafka deduplication patterns apply here too.