How to Monitor Your API for Downtime (Step-by-Step Guide for 2026)

Why API Monitoring Is Different from Website Monitoring

When a website goes down, users see a broken page. They know something is wrong. When an API goes down, something much worse happens: your users' applications silently break. Buttons stop working. Data stops loading. Payments fail. But users see no clear error message — just a broken experience.

API monitoring is more complex than website monitoring for several reasons:

• APIs can return HTTP 200 but with malformed or empty responses
• Authentication (API keys, tokens) adds another failure point
• Rate limiting can make an API appear "down" for some users but not others
• Response time degradation is a critical metric — not just binary up/down
• Individual endpoints can fail while others work fine

This guide covers how to monitor your API properly — from basic uptime checks to response validation.

Step 1: Identify Which API Endpoints to Monitor

You don't need to monitor every endpoint. Focus on the ones your users depend on most:

• Health/status endpoint: If you have one (e.g., /api/health or /api/status), monitor this first — it's designed for monitoring tools
• Authentication: Login endpoint — if this breaks, nobody can use your service
• Core functionality: The 2–3 endpoints your service is built around (e.g., /api/products for an e-commerce API, /api/send for an email service)
• Webhook receiver: If your service receives webhooks (Stripe, GitHub, etc.), monitor the endpoint accepting them
• Payment endpoints: Any endpoint involved in transactions deserves dedicated monitoring

Rule of thumb: If it breaking for 10 minutes would cause user complaints, it should be monitored.

Step 2: Determine What a "Healthy" Response Looks Like

For each endpoint, define success criteria beyond just HTTP 200:

• Status code: Which codes indicate healthy? (200, 201, 204?) Which indicate errors? (400+ is usually a problem)
• Response body: Does the response contain expected keys? (e.g., does /api/health return {"status": "ok"}?)
• Response time threshold: What latency is acceptable? Flag if response exceeds 1000ms, alert if it exceeds 3000ms
• Response size: An empty response body from an endpoint that should return data is a problem — even if it returns 200

Step 3: Configure Authentication for Monitored Endpoints

Most production API endpoints require authentication. Your monitoring tool needs to authenticate the same way your users do:

API Key Authentication

For APIs using API keys in headers (the most common pattern), configure your monitor to send:

Authorization: Bearer YOUR_MONITORING_API_KEY
X-API-Key: YOUR_MONITORING_API_KEY

Security tip: Create a dedicated monitoring API key with read-only permissions. Never use a production admin key in monitoring tools.

Basic Authentication

Authorization: Basic [base64(username:password)]

OAuth/JWT Tokens

JWT tokens expire, making them tricky for monitoring. Solutions:

• Use a long-lived token specifically for monitoring
• Monitor a public endpoint that proxies an authenticated call
• Use AlertSleep's custom header support to send static tokens

Step 4: Set Up API Monitoring with AlertSleep

Here's how to set up API endpoint monitoring in AlertSleep:

1. Create a new monitor — select "HTTP/API Monitor" type
2. Enter your endpoint URL — e.g., https://api.yourservice.com/health
3. Select HTTP method — GET for status checks; POST if you're testing a creation endpoint
4. Add request headers — enter your authentication headers here
5. Add request body — for POST endpoints, enter the JSON body
6. Set expected status code — AlertSleep alerts if a different code is returned
7. Configure response body check — enter a string that should appear in the response (e.g., "status":"ok")
8. Set response time threshold — alert if response exceeds X ms
9. Set check interval — 1-minute checks for production APIs

Step 5: Configure Alert Channels

API failures need immediate notification. Configure multiple alert channels for redundancy:

• Email: For non-urgent alerts and logging
• SMS: For high-priority endpoints — SMS gets read within minutes even when you're away from your computer
• Phone call: For critical payment or authentication endpoints — a missed SMS is still a missed alert; a phone call wakes you up
• Slack/Teams: For team awareness and coordination during incidents
• Webhook/PagerDuty: To integrate with on-call rotation systems

Step 6: Set Up API Response Time Monitoring

An API that responds in 8 seconds isn't "down" by binary definition — but it's effectively broken for users. Monitor P95 response times, not just averages:

• Under 200ms: Excellent — virtually instantaneous to users
• 200–500ms: Acceptable for most use cases
• 500ms–1s: Users notice the lag; investigate if consistent
• 1–3s: Poor performance — alert your team
• Over 3s: Critical — most user-facing features are broken

Set your monitor to alert when response time exceeds your threshold, even if the endpoint returns 200 OK.

Common API Monitoring Mistakes to Avoid

• Monitoring only the root domain (api.example.com) — add checks for specific critical endpoints
• Using a admin/superuser token — use dedicated monitoring credentials with minimal permissions
• Ignoring response body validation — a 200 with an empty body is a bug, not a success
• 5-minute check intervals for payment APIs — use 1-minute checks for anything business-critical
• Single alert channel — if the email server is down during an API outage, you won't get notified

Start Monitoring Your API in 2 Minutes

AlertSleep's API monitoring supports GET and POST requests with custom headers, request bodies, response body keyword matching, and response time thresholds. Set up your first API monitor in 2 minutes — free, no credit card required.

The free plan includes 5 monitors with 5-minute check intervals. Paid plans add 1-minute checks, SMS alerts, and phone call notifications for critical API failures.

Start monitoring your API free.