Use the free HTTP Header Parser below: your data never leaves your browser — all work happens on your device, and nothing is uploaded to any server.
What Are HTTP Headers?
HTTP headers are the labels attached to every request and response on the web. Before the actual page content, the browser and the server exchange lines like Content-Type: text/html and Cache-Control: max-age=3600. Each line has a name, a colon, and a value. Headers carry the metadata: what kind of content this is, how long it may be cached, which cookies apply, where to redirect, and which security rules the browser should enforce. You never see them in normal browsing, but they shape almost everything the browser does.
When a page behaves strangely, headers are often the reason. A page that downloads instead of displaying usually has the wrong Content-Type. A page that never updates may have an aggressive Cache-Control. A login that fails across subdomains may have a cookie scoped too narrowly. Learning to read headers turns vague problems like the site is broken into specific ones like the server sends no-store for every page, and specific problems have specific fixes.
How to Use the Parser
Copy raw headers from your browser developer tools, under the Network tab, or from a command like curl -I https://example.com, and paste them into the box. Press Parse, and the tool splits each line at the first colon into a name and a value, joins folded continuation lines back onto their header, and shows a clean table. Duplicate headers, like multiple Set-Cookie lines, stay as separate rows, because collapsing them would lose information.
Below the table, the tool checks five common security headers: Strict-Transport-Security, Content-Security-Policy, X-Content-Type-Options, X-Frame-Options, and Referrer-Policy. Missing ones are listed, so you can see at a glance what a site has not set. The Copy as JSON button gives you the same data as a JSON array, which is handy for tickets, documentation, or feeding into another script. The whole parse happens in your browser, so pasted headers never leave your machine.
Headers Worth Knowing
Content-Type tells the browser what the body is, and the charset part tells it how to decode text. Getting this wrong produces garbled characters or forced downloads. Cache-Control tells browsers and proxies how long to reuse a response, and a wrong value is a classic cause of stale content. Location carries the new address for a redirect, and it must be present on 3xx responses to be useful. Set-Cookie sets cookies, with flags like Secure, HttpOnly, and SameSite controlling where they are sent and whether scripts can read them.
Security headers are the quiet workhorses. Strict-Transport-Security tells browsers to use HTTPS only for a site, which blocks downgrade attacks. Content-Security-Policy limits which sources can load scripts and styles, which blunts cross-site scripting. X-Content-Type-Options: nosniff stops browsers from guessing a content type that differs from the declared one. X-Frame-Options and frame-ancestors control whether a page may be embedded in a frame, which blocks clickjacking. Referrer-Policy limits how much of the referring URL is shared with other sites. None of these replace careful coding, but together they raise the cost of common attacks.
A Word of Caution
Headers often contain sensitive values, especially Authorization and Cookie lines. The parser marks those rows with a warning sign as a reminder. This tool runs entirely in your browser, so pasting is safer here than into a random online tool, but the habit still matters: never paste live tokens into a public page, a shared screenshot, or a support ticket without removing them first. Tokens are passwords by another name, and a leaked token is a leaked login.
When you report a header problem, paste the smallest set that shows it, and redact values that identify a session. Good bug reports name the header, quote its value, and say what you expected instead. That habit, plus a parser that turns a wall of text into a readable table, makes header debugging faster for you and clearer for anyone helping you.