HTTP / API

HTTP headers, caching, API request/response analysis.

The HTTP / API category groups together tools for inspecting and diagnosing the requests and responses that flow between websites and APIs. You can check HTTP response headers and status codes (200, 301, 404, 500, and so on), verify that caching headers like Cache-Control and ETag are set correctly, confirm whether Gzip or Brotli compression is in use, and see whether a server is talking over HTTP/2 or HTTP/3. The same tools help you build or decode curl commands and reason about API rate limits, making them handy for backend and frontend developers, DevOps engineers, API integrators, and anyone trying to tune web performance.

A typical workflow starts by pulling the response headers and status code for a target URL to get the overall picture, then checking caching, compression, and protocol version one at a time. When you see long redirect chains or errors such as 401, 403, or 429, you trace the cause through the headers and reproduce the call with curl to compare the exact request options, which narrows the problem down fast. Most tools in this category run entirely in your browser or simply fetch a response, so there is nothing to install before you start.

cURL Command Builder

Build a runnable cURL command from method, headers and body.

cURL Command Parser

Break a cURL command into method, URL, headers and body.

Latency Percentile Calculator

Compute p50, p90, p95 and p99 from a list of response times.

HTTP Header Checker

Fetch and display the HTTP response headers of a URL.

HTTP Status & Redirect Checker

Trace the HTTP status code and full redirect chain step by step.

HTTP/2 & HTTP/3 Check

Check whether a server supports HTTP/2 (ALPN) and HTTP/3 (Alt-Svc).

CORS Configuration Check

Check a URL's CORS (Access-Control-Allow-*) headers via preflight.

API Rate Limit Calculator

Calculate safe call volume and burn-down time from per-minute/hour limits and concurrency.

Frequently asked questions

What is an HTTP status code and why does it matter?

It is a three-digit number the server returns to report the outcome of a request. 2xx means success, 3xx is a redirect, 4xx is a client error (404 not found, 403 forbidden, 429 too many requests), and 5xx is a server error. Because it is the basic signal for SEO, debugging, and monitoring, it is usually the first thing you check.

What problems can I spot from the response headers alone?

Headers reveal whether caching is in place (Cache-Control, ETag, Expires), whether compression is applied (Content-Encoding), which security settings exist (HSTS, CSP, X-Content-Type-Options), the server software, and redirect targets (Location). A single header dump often exposes missing performance or security settings at a glance.

Do I need to know curl or have coding skills to use these tools?

No. You enter a URL and the tools present the headers, status, caching, and compression results for you, so non-developers can use them too. The curl builder and parser actually help you learn curl by generating commands automatically or explaining them in plain language.

What is a rate limit?

A rate limit caps how many requests an API will accept within a time window. When you exceed it, the API typically returns 429 Too Many Requests and uses headers like X-RateLimit-Remaining and Retry-After to tell you how many calls are left and how long to wait. It is essential to account for when building reliable API integrations.

🌐 Network / IP 📡 DNS / Domain 🔒 TLS / Certificates ✉️ Email 🛡️ Web Security 🔍 SEO / Indexing 🚀 Performance / Frontend 📝 WordPress / CMS ☁️ CDN / Cloud 🛠️ Ops / SRE 💰 AdSense / Monetization