API Monitoring Checklist: What to Check Beyond a 200 OK

API monitoring means sending real requests to your API at regular intervals and checking that the answers are correct, not just that the server answered. An API that returns 200 OK with an empty list, an error message in the body or a response that takes ten seconds is broken for the apps that depend on it, even though a simple check would pass. This checklist covers what to configure so your API monitors catch real problems.

1. Choose the endpoints

Do not monitor everything. Monitor what users and integrations depend on:

• Health or status endpoint, if it checks dependencies such as the database. A health endpoint that only returns “ok” without checking anything tells you little.
• Authentication: the endpoint that issues tokens or validates sessions. If it fails, everything fails.
• Core read endpoints: the ones your app calls on every screen, such as listing orders or fetching a profile.
• Critical write paths: checkout, signup or webhook receivers, monitored with test data.
• Third-party APIs you depend on, such as payment or shipping providers, so you know when the problem is not yours.

2. Set the request: method, headers and body

A check should look like a real client request:

• Method: GET for reads, POST, PUT or PATCH for endpoints that need them.
• Headers: Accept: application/json, a Content-Type for requests with a body, and any custom headers your API requires, such as a version header.
• Body: a small, valid payload for POST requests, for example a search query.

Choose requests that are safe to repeat every minute. Avoid endpoints that create real orders, send emails or charge cards, unless you use a dedicated test account.

3. Handle authentication

Most APIs need credentials. Options:

• Basic auth for simple protected endpoints.
• API key or bearer token in a header, for example Authorization: Bearer <token>.

Create a dedicated monitoring account or token with read-only permissions. That limits the damage if the token leaks and keeps monitoring traffic separate in your logs. Remember that tokens expire. A long-lived, read-only token for monitoring avoids false alarms when a short-lived token runs out.

4. Validate the status code

Decide which status codes mean success. Usually that is 200, 201 or 204, depending on the endpoint. Treat redirects carefully: an API that suddenly redirects to a login page returns a 3xx and then a 200 with HTML. That is an outage for any app expecting JSON.

5. Validate the response content

This is where most API checks fall short. Check that the response contains something only a working API would return:

• A field that should always be present, such as "status":"ok" or "id".
• A known value from test data.
• The absence of error text, such as "error".

With Uptimecheck you set the expected response for each API monitor, together with the method, headers, body and basic auth.

6. Set response time thresholds

Slow is the new down for APIs. Mobile apps time out and integrations retry, which adds more load. Record response time on every check and set a threshold based on what is normal:

• Look at a week of response times to find the baseline.
• Set an alert threshold well above normal variation, for example two to three times the usual response time.
• Alert on sustained slowness, not single spikes. One slow request is noise, a run of them is a problem.

Checking from more than one region shows whether slowness is global or limited to one network path. Uptimecheck checks from Europe and records the response time of every check, so you can see when slowness starts.

7. Monitor the whole chain

An API rarely fails alone. Add monitors for what it depends on:

• SSL certificates on the API hostname. An expired certificate breaks every client at once.
• DNS records for the API domain.
• Server resources such as CPU, memory and disk on the API servers.
• Scheduled jobs that keep data fresh, with heartbeats.

8. Route alerts to the right people

API alerts usually belong to the developers who own the service. Send them to the team’s chat channel, and to a channel that reaches a phone for production outages at night. Use webhooks to feed alerts into your own incident tooling. See notifications.

9. Automate monitor setup

If you deploy new services often, create monitors as part of the deploy. The Uptimecheck REST API covers monitors, DNS monitors, servers, heartbeats, domains, alert channels, status pages and statistics, so monitoring can be part of your pipeline instead of a manual step afterwards.

10. Tell API consumers what is happening

If other teams or customers build on your API, give them a status page with a component for the API. It saves them from debugging their own code during your outage.

Common API monitoring mistakes

• Only checking the health endpoint. Health endpoints often pass while real endpoints fail because a dependency is down.
• Using production credentials of a real user. When that user changes their password or leaves, monitoring breaks. Use a dedicated account.
• Ignoring the body. An HTML error page with status 200 passes a status-only check.
• Alerting on every slow response. Single spikes create noise and train people to ignore alerts.
• Forgetting dependencies. The API is fine, but the certificate expired or the DNS record changed.

The checklist

1. Pick endpoints: health, auth, core reads, critical writes, key third-party APIs.
2. Set method, headers and body for each check.
3. Use a dedicated read-only token or basic auth credentials.
4. Define the expected status codes.
5. Validate content: a field or value only a working API returns.
6. Record response time and alert on sustained slowness.
7. Check from more than one region.
8. Monitor SSL, DNS, servers and scheduled jobs behind the API.
9. Route alerts to the owning team, with a phone-friendly channel for production.
10. Create monitors through the API as part of deployments.

Summary

A 200 OK is the beginning of an API check, not the end. Send realistic requests, validate the content, watch the response time and cover the chain behind the API.

API monitoring with custom methods, headers, bodies, basic auth and expected responses is part of every Uptimecheck plan. Try it free for 14 days, no credit card required.