API Response Time Tester

This tool measures the round-trip time from your browser to the API endpoint and back, including DNS lookup, TCP connection, TLS handshake, server processing, and data transfer. This gives you a realistic view of what your users experience when calling the API.

CORS (Cross-Origin Resource Sharing) errors occur when the API server doesn't allow requests from browser-based clients. This is a security feature, not a bug. APIs that support browser access will have 'Access-Control-Allow-Origin' headers. Use a REST client like Postman or curl for APIs that don't support CORS.

Under 100ms is excellent (users perceive it as instant). 100-300ms is good. 300-800ms is average and noticeable. Over 800ms users will start to disengage. Over 2 seconds is very slow and should be optimized. For user-facing APIs, aim for under 200ms at the 95th percentile.

The first request may be slower due to DNS resolution and connection establishment. Running 3-10 times gives you a better average and lets you identify variance. High variance (e.g., 50ms vs 800ms) indicates intermittent issues like rate limiting, cold starts, or network congestion.