API Monitoring: Complete Guide, REST Checks, Alerts & Best Practices

API monitoring is the continuous observation and testing of REST API endpoints to verify availability, performance, and correctness. It involves sending HTTP requests to API endpoints, validating responses, measuring performance, and alerting when APIs fail or degrade.

Unlike simple uptime checks, API monitoring verifies that APIs are not just reachable but functioning correctly—returning expected status codes, valid response structures, and acceptable performance.

What APIs Are

APIs (Application Programming Interfaces) enable software communication:

APIs power modern applications—mobile apps, web services, microservices, and third-party integrations all depend on APIs functioning correctly.

Difference Between API Monitoring and APM

Understanding the distinction helps clarify API monitoring's role:

API monitoring and APM are complementary: API monitoring verifies external API behavior from a user perspective, while APM provides internal application performance insights. Both are valuable for comprehensive observability.

Why APIs Fail Silently

APIs can fail without obvious symptoms:

• API returns errors: Server is up but API returns 500 errors
• Response structure changes: API works but response format is wrong
• Performance degradation: API works but is too slow
• Authentication failures: API is up but authentication breaks
• Data validation issues: API returns invalid data
• Contract violations: API returns unexpected responses

Why Uptime Alone is Not Enough

Simple uptime checks miss critical API issues:

API monitoring provides application-layer visibility that detects these issues before they impact users or dependent services. It validates not just that APIs are reachable, but that they function correctly.

API failures cause immediate business impact, affecting user experience, revenue, integrations, and service reliability.

User Experience Impact

API failures directly affect users:

API failures create immediate user-visible problems, leading to frustration, abandonment, and churn.

Revenue Impact

API failures directly impact revenue:

• E-commerce APIs down prevent purchases
• Payment APIs fail block transactions
• Order APIs break prevent order processing
• Inventory APIs fail cause stock issues
• Customer-facing APIs down lose sales

API downtime directly translates to lost revenue, especially for e-commerce, SaaS, and transaction-dependent businesses.

Integration Failures

APIs power integrations:

• Third-party integrations break when APIs fail
• Microservices cannot communicate
• Webhook deliveries fail
• Data synchronization stops
• Service dependencies cascade failures

API failures create cascading effects across integrated systems, causing widespread disruption.

Microservice Failures

API failures cascade through microservice architectures:

• Service-to-service API failures break communication
• Cascading failures across dependent services
• Circuit breaker patterns require API monitoring
• Service mesh API failures
• Distributed system reliability depends on API health

Third-Party Dependency Outages

External API failures impact your services:

• Payment gateway API failures block transactions
• Email service API outages prevent notifications
• Cloud provider API failures affect infrastructure
• Integration partner API issues break workflows

Data Inconsistency

API contract violations cause data problems:

• Response structure changes break data parsing
• Missing required fields cause application errors
• Data type mismatches break business logic
• Schema changes cause integration failures

Performance Degradation

Slow APIs are often worse than down APIs:

• Slow response times degrade user experience
• Timeouts cause failures
• Performance issues indicate capacity problems
• Gradual degradation goes unnoticed without monitoring

SLA Breaches

API SLAs require monitoring for verification:

• Uptime SLAs need availability metrics
• Performance SLAs require response time tracking
• Error rate SLAs need error monitoring
• Compliance needs audit trails
• Customer contracts specify API guarantees
• SLA breaches trigger penalties and contract issues

API monitoring provides the metrics needed to verify SLA compliance and demonstrate service reliability, preventing costly SLA breaches.

API monitoring operates by sending HTTP requests to API endpoints, validating responses, measuring performance, and alerting when issues are detected.

HTTP Request Execution

Monitoring sends actual HTTP requests:

Response Validation

Validate API responses:

• Status code validation (expect 200, detect 4xx/5xx)
• Response body structure validation
• JSON/XML schema validation
• Field presence and value checks
• Response size validation

Performance Measurement

Track API performance:

• Response time measurement
• Time to first byte (TTFB)
• Total request/response time
• Performance trend tracking
• Percentile calculations (P95, P99)

Error Detection

Detect API errors:

• HTTP error status codes (4xx, 5xx)
• Response validation failures
• Timeout errors
• Connection errors
• Error rate calculation

Multi-Location Testing

Test from multiple locations:

• Send requests from different geographic locations
• Verify global API accessibility
• Detect location-specific issues
• Measure regional performance differences

This continuous monitoring process provides real-time visibility into API health, enabling early detection and rapid resolution of issues.

Setting up API monitoring takes just a few minutes. Follow these steps to start monitoring your APIs:

Comprehensive API configuration ensures accurate monitoring that matches your API's requirements and behavior. Real-world usage patterns inform effective monitoring setup.

REST API Endpoint Monitoring

Monitor RESTful API endpoints:

• Full URL endpoint configuration
• Path parameter support
• Query parameter handling
• RESTful resource monitoring
• API version support

Custom HTTP Headers

Configure custom request headers:

• Content-Type headers
• Accept headers
• Custom API headers
• Header value validation
• Dynamic header values

Request Body Configuration

Configure request bodies for POST/PUT requests:

• JSON request body
• XML request body
• Form data body
• Raw request body
• Body template variables

Response Status Code Validation

Validate expected status codes:

JSON/XML Response Parsing

Parse and validate response formats:

• JSON parsing and validation
• XML parsing and validation
• Schema validation
• Structure validation
• Field extraction and validation

Real-World Usage Patterns

Configure monitoring to match production usage:

Comprehensive API configuration ensures monitoring accurately reflects your API's behavior and requirements, matching real-world usage patterns.

Different HTTP methods serve different purposes. Understanding method differences helps configure appropriate monitoring.

GET Request Monitoring

Monitor read-only endpoints:

• Most common method for API monitoring
• Retrieve data without side effects
• Query parameters for filtering
• Idempotent and safe
• No request body required

GET requests are ideal for monitoring because they don't modify data and can be safely executed repeatedly.

POST Request with Body

Monitor endpoints that create resources:

• Requires request body
• Creates new resources
• May have side effects
• JSON or form data body
• Returns created resource

POST monitoring requires careful configuration to avoid creating duplicate resources or causing unintended side effects.

PUT and PATCH Requests

Monitor update endpoints:

DELETE Request Support

Monitor deletion endpoints (use carefully):

Custom Method Support

Support for custom HTTP methods:

• Custom method names
• Non-standard HTTP methods
• API-specific methods

Method selection should match your API's design. GET is recommended for monitoring when possible.

Most APIs require authentication. Configuring proper authentication ensures monitoring can access protected endpoints while maintaining security.

API Key Authentication

Use API keys for authentication:

• API key in header (X-API-Key, Authorization)
• API key in query parameter
• Secure key storage
• Key rotation support

Bearer Token Support

OAuth 2.0 Bearer tokens:

• Authorization: Bearer <token> header
• Token refresh support
• Token expiration handling
• Secure token storage

Basic Authentication

HTTP Basic Auth:

• Username and password
• Base64 encoded credentials
• Authorization header format
• HTTPS recommended

OAuth 2.0 Flows

Full OAuth 2.0 support:

Custom Header Authentication

Custom authentication methods:

• Custom header-based auth
• Signature-based authentication
• API-specific auth schemes

Secure Credential Handling

Security best practices:

• Encrypt credentials at rest
• Never log credentials in monitoring logs
• Use least-privilege credentials (monitoring-only permissions)
• Rotate credentials regularly
• Use HTTPS for all API calls
• Store credentials in secure vaults

Learn more about security best practices

Proper authentication configuration ensures monitoring can access protected APIs while maintaining security and compliance.

Detailed request configuration ensures monitoring requests match your API's requirements exactly.

Request Headers Setup

Configure all required headers:

• Content-Type (application/json, application/xml)
• Accept headers for response format
• User-Agent for identification
• Custom API headers
• Dynamic header values

Query Parameters

Configure query string parameters:

• Query parameter configuration
• Parameter encoding
• Dynamic parameter values
• Parameter validation

Request Body Formatting

Format request bodies correctly:

• JSON body formatting
• XML body formatting
• Form data encoding
• Raw body content
• Body template variables

Content-Type Configuration

Set appropriate Content-Type:

• application/json for JSON APIs
• application/xml for XML APIs
• application/x-www-form-urlencoded for forms
• multipart/form-data for file uploads
• Custom content types

Custom Request Options

Additional request configuration:

• Request timeout configuration
• Follow redirects setting
• SSL certificate validation
• Custom user agents
• Request retry configuration

Comprehensive request configuration ensures monitoring requests are correctly formatted and match your API's expectations.

Response validation ensures APIs return correct data, not just successful status codes. Comprehensive validation detects subtle API issues and contract violations.

Why "200 OK" is Not Always Success

Status codes alone don't guarantee API correctness:

Response validation beyond status codes is essential to detect these issues that simple uptime checks miss.

Status Code Validation

Validate expected status codes:

Response Body Validation

Validate response content:

• Response body presence
• Response format validation
• Required field checks
• Field value validation
• Response size limits

JSON Schema Validation

Validate JSON structure:

• JSON schema validation
• Structure validation
• Type validation (string, number, boolean)
• Required field validation
• Nested object validation

Response Time Thresholds

Alert on slow responses:

• Maximum response time thresholds
• Warning and critical thresholds
• Performance degradation alerts
• Baseline comparison

Response Size and Format Checks

Validate response characteristics:

• Maximum response size limits
• Minimum response size validation
• Response format validation (JSON, XML)
• Content-Type header validation
• Unexpected size or format detection

Contract Checking

Verify API contracts are maintained:

• Verify API contract compliance
• Detect breaking changes
• Validate response schemas
• Check backward compatibility
• Monitor contract violations

Comprehensive response validation and contract checking detects API issues beyond simple availability, ensuring APIs function correctly and maintain contracts.

Performance monitoring tracks API response times, identifies bottlenecks, and detects performance degradation before it impacts users.

Response Time Tracking

Measure API response times:

• Total response time
• Time to first byte (TTFB)
• DNS resolution time
• Connection establishment time
• Data transfer time

API Uptime Calculation

Track API availability:

• Uptime percentage calculation
• Downtime event tracking
• SLA compliance monitoring
• Availability reports

Performance Metrics

Comprehensive performance metrics:

Response Time Graphs

Visualize performance trends:

• Historical response time graphs
• Performance trend visualization
• Baseline comparison
• Performance anomaly detection

Performance Regression Detection

Detect performance degradation:

• Compare current performance to baselines
• Detect gradual performance degradation
• Identify performance regressions
• Alert on significant performance changes

Performance Trends

Analyze performance over time:

• Identify gradual performance degradation
• Detect performance patterns
• Compare current vs historical performance
• Capacity planning insights

Performance monitoring provides actionable insights for API optimization and capacity planning, enabling proactive performance management.

Comprehensive error detection and handling ensures API issues are identified and addressed quickly.

4xx vs 5xx Errors

Understanding error categories helps prioritize response:

4xx errors typically indicate client-side issues (authentication, request format), while 5xx errors indicate server-side problems requiring immediate attention.

Error Status Code Detection

Detect HTTP error codes:

• Automatic detection of 4xx and 5xx status codes
• Network error detection (connection failures, timeouts)
• DNS error detection
• SSL/TLS error detection

Error Response Parsing

Extract error information:

• Parse error response bodies
• Extract error messages
• Identify error types
• Error code extraction

Error Rate Monitoring

Track error frequency:

• Error rate calculation
• Error rate thresholds
• Error rate alerts
• Error rate trends

Error Alert Configuration

Configure error alerts:

• Alert on specific error codes
• Error rate threshold alerts
• Error pattern detection
• Error escalation policies

Error Spikes

Detect sudden error increases:

• Detect sudden error rate increases
• Alert on error spikes
• Identify error patterns
• Correlate errors with other events

Recovery Detection

Monitor error resolution:

• Track error duration
• Monitor recovery time
• Error resolution confirmation
• Automatic recovery notifications

Error Trend Analysis

Analyze error patterns over time:

• Error rate trends
• Error pattern identification
• Error history analysis
• Predictive error detection

Comprehensive error handling and error rate monitoring provides visibility into API issues and enables rapid incident response.

Multi-location API testing verifies global accessibility and detects regional performance issues.

Multi-Location API Testing

Test APIs from multiple locations:

• 60+ global monitoring locations
• Verify API accessibility worldwide
• Detect location-specific issues
• Confirm global service availability

Geographic Performance

Measure performance by region:

• Regional response time comparison
• Geographic performance analysis
• Location-specific metrics
• Regional optimization insights

Regional Availability

Verify regional service availability:

• Test from North America, Europe, Asia, Australia
• Detect regional outages
• Verify CDN and regional deployments
• Confirm multi-region service availability

Location-Specific Results

View results per location:

• Per-location API status
• Location-specific response times
• Regional performance comparison
• Location-based alerting

Global API Monitoring

Comprehensive global visibility:

• Worldwide API accessibility
• Global performance metrics
• International connectivity validation
• Multi-region service verification

Multi-location monitoring ensures APIs are accessible and performant globally, not just from specific regions.

Accurate uptime calculation and SLA monitoring provide visibility into API reliability and help verify compliance with service level agreements.

Uptime Percentage Calculation

Calculate API uptime accurately:

Accurate uptime calculation requires consistent monitoring intervals and proper definition of what constitutes downtime (errors, timeouts, validation failures).

Downtime Tracking

Track all downtime events:

• Start and end timestamps for each downtime event
• Downtime duration calculation
• Downtime reason tracking (error type, timeout, validation failure)
• Recovery time measurement
• Downtime event history

SLA Monitoring

Monitor SLA compliance:

• Uptime SLA tracking (e.g., 99.9% uptime)
• Performance SLA monitoring (response time guarantees)
• Error rate SLA compliance
• SLA breach detection and alerts
• SLA compliance reports

Reporting Accuracy

Ensure accurate reporting:

• Exclude maintenance windows from uptime calculations
• Account for scheduled downtime
• Handle monitoring gaps appropriately
• Provide transparent uptime reporting

Accurate uptime calculation and SLA monitoring provide visibility into API reliability and help maintain compliance with service level agreements.

Rate limit and version monitoring detect API throttling, version changes, and backward compatibility issues that can break integrations.

Rate Limit Detection

Detect when APIs are rate-limited:

• 429 (Too Many Requests) status code detection
• Rate limit header monitoring (X-RateLimit-Remaining, Retry-After)
• Throttling detection
• Rate limit approaching alerts

Rate limit detection helps identify when APIs are being throttled, enabling optimization of request patterns and prevention of service degradation.

Throttling Alerts

Alert on rate limiting:

• Immediate alerts on 429 responses
• Rate limit threshold warnings
• Throttling pattern detection
• Rate limit recovery tracking

Rate Limit Tracking

Track rate limit usage:

• Monitor rate limit headers
• Track remaining request quota
• Rate limit trend analysis
• Capacity planning insights

API Version Change Detection

Detect API version changes:

• Monitor API version headers
• Detect version number changes
• Track version deprecation warnings
• Version migration alerts

Backward Compatibility Risks

Monitor for breaking changes:

• Response structure changes
• Field removal or type changes
• Endpoint deprecation
• Breaking change detection

Version monitoring helps detect API changes that could break integrations, enabling proactive migration and preventing service disruption.

Rate Limit Optimization

Optimize rate limit usage:

• Identify rate limit patterns
• Optimize request frequency
• Plan for rate limit increases
• Monitor rate limit efficiency

Rate limit and version monitoring help maintain API reliability and prevent integration failures from throttling or breaking changes.

Immediate notifications ensure API issues are detected and addressed quickly, minimizing impact on users and services.

API Downtime Alerts

Instant alerts when APIs fail:

• Real-time API failure detection
• Detailed error information
• Endpoint-specific alerts
• Immediate notification delivery

Performance Degradation Alerts

Alert on slow performance:

• Response time threshold alerts
• Performance degradation warnings
• Baseline comparison alerts
• Slow API detection

Error Rate Alerts

Alert on high error rates:

• Error rate threshold alerts
• Error spike detection
• Error pattern alerts
• Error trend warnings

Multi-Channel Notifications

Receive alerts through multiple channels:

Escalation Policies

Escalate critical API issues:

• Notify additional team members if alerts aren't acknowledged
• Escalate to management for critical APIs
• Activate incident response procedures
• Multi-level escalation workflows

Effective notification ensures API issues receive immediate attention through appropriate channels.

Organizing APIs into groups and using tags enables efficient management of large API portfolios.

Create API Groups

Organize APIs into groups:

• Group by service (authentication, payment, data)
• Group by environment (production, staging, dev)
• Group by priority (critical, high, standard)
• Group by team or ownership

Group-Based Alerts

Configure alerts per group:

• Group-specific notification channels
• Group-based escalation policies
• Group alert thresholds
• Group status aggregation

Group Statistics

Aggregate metrics per group:

• Group uptime percentage
• Group average response time
• Group error rate
• Group performance trends

Tag API Endpoints

Use tags for flexible organization:

• Apply multiple tags per API
• Tag-based filtering
• Tag-based reporting
• Dynamic organization

Tag-Based Filtering

Filter and view APIs by tags:

• Filter by single or multiple tags
• Tag-based dashboards
• Tag-based alerts
• Tag-based exports

Groups and tags provide flexible organization for managing large API portfolios efficiently.

Comprehensive dashboards and reports provide visibility for stakeholders, compliance documentation, and operational insights.

API Overview Dashboard

Centralized API visibility:

• Real-time API status overview
• Performance metrics at a glance
• Error rate visualization
• Active alerts summary

Custom Dashboards

Create custom dashboard views:

• Custom metric visualizations
• API-specific dashboards
• Team-specific views
• Role-based dashboard access

API Availability Reports

Detailed availability reporting:

• Uptime percentage per API
• Downtime event summaries
• Availability trends
• SLA compliance reports

API Performance Reports

Performance analysis reports:

• Response time analysis
• Performance trend reports
• Percentile analysis
• Performance optimization insights

Export API Data

Export data for external analysis:

Comprehensive dashboards and reports provide visibility and documentation for stakeholders, compliance, and decision-making.

API access and automation enable integration with existing workflows, CI/CD pipelines, and automated incident response.

API Monitoring APIs

Programmatic access to monitoring:

• Check API status via REST API
• Retrieve monitoring data
• Trigger on-demand checks
• Manage API configurations
• Access historical data

Webhook Payloads

Real-time webhook notifications with detailed payloads:

• Instant webhook alerts on API failures
• Recovery confirmation webhooks
• Status change notifications
• Detailed payload information (status, response time, error details)
• Custom webhook payload formatting

CI/CD Integration

Integrate with deployment pipelines:

• Automatic API monitor creation in CI/CD
• Infrastructure-as-code integration
• Deployment verification
• Post-deployment API health checks

Automated Workflows

Automate monitoring processes:

• Automatic API monitor creation
• Automated incident response
• Workflow automation
• Integration with ticketing systems

API integration and automation enable efficient API monitoring and seamless integration with existing infrastructure and workflows.

Following best practices ensures effective API monitoring that provides value without overwhelming teams or causing false positives.

Monitor All Critical Endpoints

Comprehensive coverage is essential:

• Monitor authentication APIs
• Track payment and transaction APIs
• Monitor customer-facing endpoints
• Track internal service APIs
• Monitor third-party API integrations

Missing even one critical API can lead to undetected failures. Maintain a complete API inventory and ensure all critical endpoints are monitored.

Validate Response Structure

Don't just check status codes:

• Validate response body structure
• Check required fields are present
• Verify field types and values
• Use JSON schema validation
• Detect response format changes

Response validation detects API issues that status code checks miss, ensuring APIs return correct data, not just successful responses.

Use Realistic Payloads

Test with realistic request data:

• Use production-like request bodies
• Include realistic query parameters
• Test with actual data formats
• Validate with real-world scenarios
• Avoid minimal test payloads

Realistic payloads ensure monitoring accurately reflects production API behavior and detects issues that minimal test data might miss.

Monitor from Multiple Locations

Verify global accessibility:

• Test from different geographic locations
• Verify reachability across ISPs
• Detect location-specific issues
• Confirm global API availability

Track Trends, Not Just Alerts

Monitor performance trends:

• Track response times over time
• Monitor error rates and trends
• Identify gradual performance degradation
• Detect patterns before they become critical
• Use trends for capacity planning

Best practices evolve with your APIs. Regular review and adjustment ensure monitoring remains effective as APIs change.

Understanding common API monitoring issues helps resolve problems quickly and reduce false positives.

Authentication Failures

API authentication may fail:

Solution: Verify credentials are correct and not expired. Check token refresh configuration. Ensure credential format matches API requirements.

Timeout Issues

Requests may timeout:

• API response too slow
• Network latency issues
• Timeout value too short
• API overloaded

Solution: Adjust timeout values based on actual API response times. Investigate API performance if timeouts are frequent.

False Positive Alerts

Alerts for non-issues:

• Transient network issues
• Response validation too strict
• Temporary API slowdowns
• Expected maintenance

Solution: Use retry logic, adjust validation rules, configure maintenance windows, and review alert thresholds.

Response Validation Errors

Validation may fail incorrectly:

• Response structure changed
• Validation rules too strict
• Optional fields treated as required
• Schema validation errors

Solution: Review validation rules, update schemas if API changed, and adjust validation to match actual API behavior.

Network Connectivity Problems

Network issues affect monitoring:

• ISP or datacenter network failures
• DNS resolution problems
• Routing issues
• DDoS attacks

Solution: Verify network connectivity, check DNS resolution, test from different locations, and coordinate with network team.

API monitoring serves diverse use cases across application architectures, integrations, and service types.

REST API Monitoring

Monitor RESTful APIs:

• REST endpoint availability
• REST API performance
• RESTful service health
• REST API error detection

Microservices Monitoring

Monitor microservice APIs:

• Service-to-service API calls
• Microservice health checks
• Inter-service communication
• Service dependency monitoring

Third-Party API Monitoring

Monitor external API dependencies:

• Payment gateway APIs
• Email service APIs
• Cloud provider APIs
• Integration partner APIs

Internal API Monitoring

Monitor internal service APIs:

• Internal service endpoints
• Backend API health
• Internal service communication
• Service mesh APIs

Public API Monitoring

Monitor public-facing APIs:

• Public API endpoints
• Developer API availability
• Public service APIs
• Customer-facing APIs

API monitoring should be accessible to everyone, from individual developers to large enterprises managing complex API infrastructures.

Free API Monitoring

The free plan provides comprehensive API monitoring:

No credit card required. The free plan is free forever—upgrade only when you need advanced features like extended retention, bulk monitoring, or API access.

When Users Typically Upgrade

Common reasons to upgrade from the free plan:

• Scale: Need to monitor many APIs (10+)
• Frequency: Require more frequent checks (less than 5 minutes)
• Retention: Need more than 30 days of historical data
• Automation: Need API access or webhook integration
• Teams: Multiple team members need access

Why Paid Plans Add Value

Paid plans provide additional capabilities: