API Uptime Monitoring: How to Monitor REST APIs 24/7

Your API is a product. If it’s down, your customers’ products are broken. API uptime monitoring goes beyond simple HTTP checks to validate that your API is returning correct data, within acceptable latency, for every critical endpoint.

What Makes API Monitoring Different

Website monitoring checks if a page loads. API monitoring must verify:

• Status codes — 200 for success, correct error codes for edge cases
• Response body — JSON structure, required fields, correct data types
• Response time — Under your published SLA threshold
• Authentication — API keys, OAuth tokens, and auth flows working correctly
• Rate limiting — Not accidentally blocking legitimate traffic

Setting Up API Monitoring

Step 1: Identify Critical Endpoints

Monitor these first:

• Health check endpoint (/health or /api/v1/status) — Your canary
• Authentication endpoint — Login/token refresh flows
• Most-used endpoints — Check your API analytics for the top 5
• Revenue-critical endpoints — Payment processing, subscription management

Step 2: Define Success Criteria

For each endpoint, define what “up” means:

GET /api/v1/health
Expected: 200 OK
Expected body contains: "status": "ok"
Max response time: 500ms

Simple status code checks miss failures where the server returns 200 but with wrong data. Always validate response content for critical endpoints.

Step 3: Set Check Frequency

Match your SLA target:

• Public API with SLA: Check every 10-30 seconds
• Internal API: Check every 1-2 minutes
• Non-critical endpoints: Check every 5 minutes

Step 4: Configure Multi-Region Checks

If your API serves global users, monitor from multiple regions. An API that works from US-East but fails from EU-West is a regional outage that single-region monitoring won’t catch.

API-Specific Monitoring Patterns

Chain Monitoring

Test dependent request sequences:

1. Authenticate → get token
2. Use token to fetch data
3. Verify response matches expected structure

If step 1 fails, steps 2-3 will fail too. Chain monitoring catches auth system failures early.

Schema Validation

Verify response bodies match your API specification. A deployment that changes a field from string to number won’t trigger a status code alert but will break every client.

Latency Monitoring

Track P95 and P99 latency for each endpoint. Alert when percentiles exceed your published SLA threshold, not just when the endpoint is fully down.

Error Rate Monitoring

A 5% error rate might not trigger a “down” alert, but it’s burning your error budget and affecting users.

Common API Failure Modes

1. Deployment breaks backward compatibility — New response format breaks clients
2. Database connection pool exhaustion — API returns 500 under load
3. SSL certificate expiry — Instant total failure for all HTTPS clients
4. Rate limit misconfiguration — Legitimate traffic blocked by overly aggressive limits
5. Upstream dependency failure — Third-party API or database goes down
6. Memory leak — Gradual degradation until OOM restart

Monitoring catches all of these if you check frequently enough and validate response content, not just status codes.

Communicating API Status

Your API consumers need to know when something is wrong:

1. Status page — Real-time component status for each API version/service
2. Incident feed — Timeline of current and past incidents
3. Uptime graph — Visual availability history builds trust
4. Subscription — Let consumers subscribe to updates

Transparency about downtime actually increases trust. Users prefer knowing about issues to discovering them through their own errors.

Join the Warden waitlist for API monitoring with 10-second checks, response validation, and built-in status pages.

Related tools:

• Uptime Calculator — Define your API SLA target
• HTTP Status Codes — Reference for API response codes
• Latency Percentile Calculator — Analyze API response times