Third-Party API Integration Pre-Launch Checklist: 18 Things to Verify Before You Ship

Integrations fail in production in ways they never fail in development. The third-party service goes down. A rate limit you did not know existed kicks in. A webhook fires before your database is ready. The auth token expires at 2 AM on a Sunday. None of these show up in a happy-path test.

This checklist is designed to be run before you flip the production switch on any third-party integration.

Authentication and Secrets

• Secrets are outside source control. No API keys, client secrets, or webhook signing keys in .env files committed to the repo. Use environment variables loaded from a secrets manager (AWS Secrets Manager, Doppler, Vault).
• Token expiry is handled. OAuth access tokens expire. Your integration proactively refreshes tokens before expiry, not reactively after a 401. Test this by shortening the expiry in your staging environment.
• Secrets can be rotated without a deploy. If a key is compromised, you need to rotate it in minutes, not hours. Verify the rotation path is fast and tested.
• Permissions are scoped to minimum required. Your API credentials only have the permissions the integration actually needs. Read-only where possible.

Error Handling and Resilience

• Every API call has a timeout. Never make an HTTP request without a timeout. A hanging request can block a thread pool or exhaust a connection pool. Set aggressive timeouts (5–15 seconds for most integrations) and handle the timeout error explicitly.
• Rate limit responses are handled. When the API returns 429, your code backs off and retries after the Retry-After header value, or with exponential backoff if the header is absent. Verify this logic is exercised in your staging environment.
• 5xx responses from the provider are retried with backoff. A transient 503 should not permanently fail an operation. Implement retry logic with exponential backoff and a ceiling on retries.
• 4xx responses do not retry blindly. A 400 Bad Request or 404 Not Found usually signals a bug in your code, not a transient failure. Log it clearly and alert; do not loop.
• Circuit breaker or fallback exists for critical paths. If the third-party service goes down, what does your application do? For non-critical integrations, fail gracefully and queue for later. For critical paths, a circuit breaker prevents cascade failures.

Webhook-Specific Checks

• Signature verification is implemented and tested. Verify every inbound webhook against the provider's HMAC signature before processing. Test with a tampered payload — it should return 401.
• Endpoint returns 200 before doing slow work. Acknowledge receipt immediately; process asynchronously. Verify that the processing path actually runs even if the HTTP response is already sent.
• Idempotency is in place. Replay the same webhook event twice against your staging endpoint. Confirm the outcome is identical to processing it once. Check for duplicate records, duplicate emails, or double-charged amounts.
• Endpoint URL is stable and versioned. Changing your webhook URL requires updating every provider registration. Use a stable path like /webhooks/v1/stripe rather than /api/payments/callback.

Rate Limits and Quotas

• You know the provider's rate limits. Read the documentation; do not discover limits in production. Note whether limits are per second, per minute, per hour, or per day.
• Your expected load is under the limit with headroom. At peak load, how many API calls per minute will you make? Model this, including spikes.
• You have a plan for limit increases. Some providers require manual approval for higher limits. Apply before you need it.

Observability

• Every API call is logged with its outcome. Log the provider, endpoint, HTTP status, and latency for every call. Do not log sensitive request/response bodies, but do log enough to diagnose failures.
• Alerts exist for elevated error rates. Set up an alert if the error rate for a given integration exceeds a threshold (e.g., more than 5% of calls returning 5xx over 5 minutes).
• You can trace a failing event end-to-end. Given a webhook event ID or transaction ID from the provider, can you find every log line related to it? Correlation IDs make this possible.

One Final Check

Run a chaos test: turn off the staging integration and verify your application degrades gracefully. No unhandled exceptions, no silent data loss, no user-facing crashes.

If any item on this list is incomplete, the integration is not ready for production — regardless of how well it worked in testing.

Building integrations that hold up under real-world conditions is a core part of what Clixo does for product teams. If you want the integration built right from the start, let us know what you are working on.