Your API returns 200 OK. Everything looks fine. But your mobile app can't authenticate users, your webhook isn't processing payments, and your integration partners are sending angry emails.
API monitoring goes beyond checking if your endpoint responds. It validates that your API actually works—returns correct data, handles authentication, completes transactions, and performs within acceptable limits.
This guide covers API monitoring fundamentals: what to check, how to check it, and how to get alerted when something breaks. Whether you're running a simple REST API or a complex multi-service architecture, these principles apply.
New to monitoring in general? Start with What is Uptime Monitoring for the fundamentals.
What is API monitoring?
API monitoring is the practice of regularly testing your API endpoints to ensure they're available, responding correctly, and performing within acceptable parameters.
Beyond Simple Uptime
Basic website monitoring asks: "Does this URL return a 200 status code?"
API monitoring asks more:
- Does the endpoint respond at all?
- Is the response valid JSON/XML?
- Does the response contain expected data?
- Is authentication working?
- Is the response time acceptable?
- Do multi-step workflows complete successfully?
An API can return 200 OK while being completely broken. The database might be returning empty results. The authentication service might be rejecting valid tokens. The response might be malformed. API monitoring catches these scenarios.
This is why uptime alone isn't enough—especially for APIs.
Who Needs API Monitoring?
- SaaS products: Your API is your product; if it's down, you're down
- Mobile app backends: App users hit your API constantly
- Integration providers: Partners depend on your API reliability
- Internal services: Microservices need to know when dependencies fail
- Webhook receivers: You need to know if incoming webhooks are being processed
Why monitor APIs?
APIs Fail Differently Than Websites
When a website fails, users see an error page. When an API fails, the failure can be invisible—or worse, silent.
Common API failure modes:
- Partial failures: 9 out of 10 endpoints work, but the critical one doesn't
- Data corruption: API responds but returns wrong data
- Silent timeouts: Requests hang forever instead of failing fast
- Auth degradation: New tokens fail while existing sessions work
- Rate limit issues: Some clients get blocked while others don't
Your Users Can't Tell You
When your website is slow, users complain. When your API is slow, the app just feels broken—users don't know why. They'll uninstall your app before they'll debug your API.
For B2B APIs, your integration partners might not notice failures for hours or days. By then, data is lost or corrupted.
Third-Party Dependencies
Your API probably calls other APIs: payment processors, auth providers, email services, databases. When they fail, your API fails. Monitoring lets you distinguish between "our code is broken" and "Stripe is having an outage."
The Cost of API Downtime
API downtime can be more expensive than website downtime:
- Mobile apps become unusable
- Integration partners lose trust
- Automated workflows break
- Data synchronization fails
- Webhooks are missed permanently
Calculate the impact: Downtime revenue calculator.
Types of API monitoring
1. Availability Monitoring (Uptime)
The most basic check: is the API endpoint reachable and responding?
- • Send HTTP request to endpoint
- • Check for successful status code (200, 201, etc.)
- • Verify response is received within timeout
Catches: Server crashes, network issues, DNS problems, complete outages
Misses: Application errors returning 200, data issues, auth problems
Learn more: HTTP/HTTPS monitoring.
2. Response Validation
Goes beyond status codes to validate the actual response content.
- • Verify response is valid JSON/XML
- • Check for required fields in response
- • Validate data types and formats
- • Assert specific values or patterns
Example: Your /api/users endpoint should return a JSON array with at least one user object containing "id" and "email" fields.
Catches: Malformed responses, missing data, serialization errors, database connection issues
3. Performance Monitoring
Track response times and ensure they stay within acceptable limits.
- • Measure time to first byte (TTFB)
- • Track total response time
- • Set thresholds for acceptable performance
- • Alert on degradation before it becomes an outage
Key insight: Slow APIs often precede failed APIs. If response times are trending up, investigate before it crashes.
4. Multi-Step Transaction Monitoring
Test complete workflows that span multiple API calls.
- Authenticate (POST /auth/login)
- Use token to fetch data (GET /api/data)
- Modify data (PUT /api/data/123)
- Verify change persisted (GET /api/data/123)
Catches: Auth failures, state management bugs, transaction issues, race conditions
Details: Process monitoring for multi-step flows.
5. SSL/TLS Monitoring
APIs using HTTPS need valid, non-expired certificates.
- • Track certificate expiration dates
- • Validate certificate chain
- • Check for proper TLS configuration
- • Alert before certificates expire
An expired API certificate doesn't just show a warning—most API clients will refuse to connect entirely.
Learn more: SSL certificate monitoring.
What to monitor in your API
You can't (and shouldn't) monitor every endpoint. Focus on what matters:
Critical Endpoints First
Prioritize monitoring for:
- Authentication endpoints: If login fails, everything fails
- Core business logic: The main thing your API does
- Payment/transaction endpoints: Money is involved
- Third-party integrations: External dependencies you can't control
- Health check endpoint: Your API's self-reported status
Real example: How to monitor SaaS login & auth flows.
What to Validate
For each monitored endpoint, decide what constitutes "success":
Basic (minimum):
- • Status code is 2xx
- • Response time < 5 seconds
Better:
- • Status code is exactly 200
- • Response time < 1 second
- • Response is valid JSON
- • Response contains expected fields
Comprehensive:
- • All of the above
- • Specific field values are correct
- • Data types match schema
- • Business logic assertions pass
Don't Forget Error Handling
Monitor that your error responses are also correct:
- Invalid requests should return 400, not 500
- Unauthorized requests should return 401/403
- Not found should return 404
- Error responses should have helpful messages
If your API returns 200 for errors (a common anti-pattern), you need response body validation to catch failures.
Setting up health checks
A health check endpoint is a dedicated URL that reports your API's status. It's the foundation of API monitoring.
Basic Health Check
At minimum, a health endpoint confirms the API is running:
GET /health
Response: 200 OK
{
"status": "healthy",
"timestamp": "2026-01-29T10:00:00Z"
}
Comprehensive Health Check
A better health check tests actual dependencies:
GET /health
Response: 200 OK
{
"status": "healthy",
"checks": {
"database": {
"status": "healthy",
"responseTime": 12
},
"redis": {
"status": "healthy",
"responseTime": 3
},
"stripe": {
"status": "healthy",
"responseTime": 145
}
},
"version": "2.4.1",
"timestamp": "2026-01-29T10:00:00Z"
}
Health Check Best Practices
- Keep it fast: Health checks should respond in <500ms
- Don't cache: Return real-time status, not cached results
- Test real dependencies: Actually ping the database, don't just check if the connection pool exists
- Use appropriate status codes: Return 503 if unhealthy, not 200 with "status": "unhealthy"
- Don't expose secrets: Health endpoints shouldn't reveal sensitive configuration
- Version your health check: Include API version for debugging
Shallow vs Deep Health Checks
Some teams implement two endpoints:
- /health/live: Shallow check—is the process running? (for Kubernetes liveness probes)
- /health/ready: Deep check—can we serve traffic? (for readiness probes)
For external monitoring, use the deep check. You want to know if the API can actually handle requests, not just that the container is alive.
Multi-step API monitoring
Real API usage involves multiple calls in sequence. A single endpoint being "up" doesn't mean the workflow works.
Why Multi-Step Matters
Consider a typical e-commerce API flow:
- User authenticates → gets token
- User adds item to cart → cart ID returned
- User initiates checkout → payment intent created
- Payment processed → order confirmed
Each step can work independently but fail when combined:
- Auth works, but the token isn't accepted by the cart endpoint
- Cart works, but the cart ID isn't found by checkout
- Checkout works, but the payment callback fails
Implementing Multi-Step Monitoring
A multi-step monitor executes requests in sequence, passing data between steps:
Step 1: POST /auth/login → Extract: access_token Step 2: GET /api/profile → Header: Authorization: Bearer {access_token} → Validate: response.user.id exists Step 3: POST /api/orders → Header: Authorization: Bearer {access_token} → Body: { "items": [...] } → Validate: response.order_id exists
If any step fails, you know exactly where the workflow breaks.
Detailed example: Monitoring your SaaS authentication flow.
See also: Shopify checkout monitoring and WooCommerce checkout monitoring for e-commerce examples.
What to Test in Multi-Step Flows
- Authentication flows: Login, token refresh, logout
- CRUD operations: Create, read, update, delete cycles
- Transaction flows: Cart → checkout → payment → confirmation
- Data synchronization: Write to one endpoint, verify via another
Alerting best practices for API monitoring
Reduce False Positives
APIs can have brief hiccups that don't affect users. Don't alert on every blip:
- Confirmation checks: Require 2-3 consecutive failures before alerting
- Multi-region validation: Alert only if multiple regions report failure
- Reasonable timeouts: Set timeouts appropriate for your API's normal response time
Why multi-region matters: Multi-region monitoring.
Alert on the Right Channels
Different severities need different channels:
- Critical (API completely down): PagerDuty, phone call, SMS
- Warning (degraded performance): Slack, email
- Info (recovered, maintenance): Email, dashboard only
Setup guide: Alerting and notification channels.
Include Context in Alerts
A useful alert tells you:
- • What failed (endpoint, check type)
- • When it failed (timestamp)
- • How it failed (status code, error message, timeout)
- • Where it failed (which region)
- • How long it's been down (duration)
- • Link to more details (dashboard, logs)
Bad alert:
"API check failed"
Good alert:
"POST /api/auth/login returning 503 from EU region for 5 minutes. Last success: 10:42 UTC. Dashboard: [link]"
Communicate Externally
When your API has issues, your users and integration partners need to know. A status page provides a single source of truth during incidents.
Set one up: Status pages or try the emergency status page (no signup required).
Best practices: Communicating incidents clearly.
Common API monitoring mistakes
Only Checking Status Codes
A 200 status code doesn't mean success. Your API might return:
{ "success": false, "error": "Database connection failed" }
Always validate response content, not just status codes.
Testing Without Authentication
If you only test public endpoints, you won't catch auth failures. Create a dedicated test account and monitor authenticated endpoints. Monitor the auth flow itself, not just endpoints that require auth.
Monitoring From One Location
If your monitoring runs from US-East and your EU users can't reach the API, you won't know. Use multi-region monitoring for APIs with global users.
More on this: How to check if your site is actually up for users.
Ignoring Response Time
An API that takes 30 seconds to respond is effectively down for most users. Set response time thresholds and alert when performance degrades.
Not Testing Error Paths
Your API should return proper errors for invalid requests. Consider monitoring that:
- • Invalid auth returns 401 (not 500)
- • Bad requests return 400 (not 500)
- • Rate limits return 429 (not hang indefinitely)
Alert Fatigue
If you get 50 alerts a day, you'll ignore them. When something critical happens, you'll miss it. Tune thresholds, use confirmation checks, and reserve alerts for real problems.
No Monitoring for Background Jobs
Many APIs trigger background processing: sending emails, processing payments, syncing data. These jobs can fail silently. Use heartbeat monitoring to ensure scheduled tasks complete.
Solution: Heartbeat monitoring for cron jobs and background tasks.
Getting started with API monitoring
Identify Critical Endpoints
List your API's most important endpoints: authentication, core functionality, payments, third-party integrations. Start with 3-5 endpoints. You can add more later.
Create a Health Endpoint
If you don't have one, add a /health endpoint that tests your dependencies. This becomes your primary monitoring target.
Set Up Basic Monitoring
For each endpoint: configure HTTP method and URL, add required headers, set expected status code, add response validation, set a reasonable timeout (5-30 seconds).
Need help? Monitoring without DevOps complexity walks through setup.
Configure Alerts
Set up notifications where you'll actually see them: Slack for team visibility, email as backup, SMS/phone for critical overnight issues.
Options: Alert channels.
Add a Status Page
Give your API users somewhere to check status during incidents.
Free status page generator for quick setup or full status pages for branded, custom-domain pages.
Monitor and Iterate
After a week: Are you getting too many false positives? Adjust timeouts and confirmation checks. Did you miss any real issues? Add monitoring for those endpoints. Are response times trending up? Investigate before it becomes an outage.
Frequently asked questions
How often should I monitor my API?
For production APIs, 1-5 minute intervals are standard. Critical payment or auth endpoints might warrant 1-minute checks. Less critical endpoints can use 5-minute intervals. The trade-off is faster detection vs. more load on your API (usually negligible) and potential for more false positives.
Should I monitor internal APIs?
Yes, if they're critical to your system. Internal APIs between microservices can fail and cause cascading issues. At minimum, monitor the health endpoints of critical internal services. External monitoring (from outside your network) catches different issues than internal monitoring.
How do I monitor authenticated API endpoints?
Create a dedicated test account with minimal permissions. Configure your monitoring to authenticate with these credentials. For APIs using OAuth or JWT, you'll need multi-step monitoring that first obtains a token, then uses it for subsequent requests. Rotate test credentials periodically for security.
What's the difference between API monitoring and APM?
API monitoring tests your API from the outside, like a user would—checking if endpoints respond correctly. APM (Application Performance Monitoring) instruments your code from the inside, tracking internal performance, errors, and transactions. API monitoring asks "is it working?"; APM asks "why is it slow?" Both are valuable for different purposes.
How do I reduce false positives in API monitoring?
Use confirmation checks (require 2-3 failures before alerting), multi-region monitoring (only alert if multiple locations report failure), and appropriate timeouts (don't alert on a 2-second response if your API normally takes 1.5 seconds). Also ensure your test endpoints are stable—if your test data changes frequently, validations may fail unexpectedly.
Should I monitor third-party APIs I depend on?
Yes. If your API depends on Stripe, Twilio, or any external service, their outage becomes your outage. Monitor the specific endpoints you use, not just their status pages. This helps you distinguish between "our code is broken" and "our payment provider is down" when debugging incidents.
Start monitoring your API today
API monitoring isn't complicated, but it requires thinking beyond simple uptime. Your API can return 200 OK while being completely broken for users.
Start with the basics: health endpoints, critical path monitoring, and proper alerting. Add multi-step transaction monitoring for complex workflows. Validate response content, not just status codes.
The goal isn't perfect coverage—it's knowing when something breaks before your users do.
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