HTTP Headers Viewer: Analyze & Audit Response Headers
HTTP headers viewer online: inspect request and response headers with detailed security analysis for caching, CORS, and cookies.
Updated 2026-08-16
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Features
- Paste raw HTTP response headers for instant analysis; works with curl, browser DevTools, or any HTTP client
- Automatic header categorization: General, Cache, Security, CORS, Content, Server, and Other
- Security header audit: detects missing headers like HSTS, CSP, X-Frame-Options, and more
- Severity-based security warnings (high/medium/low) to prioritize fixes
- Parse status line to display response status code and status text
- Copy individual header values or the full header list to clipboard
- Real-time analysis as you type; no button clicking needed
- Live HTTP header fetch: enter any URL and the tool fetches headers directly via your browser, no terminal or DevTools needed for quick checks
- Status line parser: extracts and displays the HTTP version, status code, and reason phrase separately for quick status interpretation
- Header count and size statistics: see how many headers the server returned and an approximate total size to assess server response efficiency
- Multi-value header support: correctly parses headers that appear multiple times (like Set-Cookie, WWW-Authenticate) and displays each value separately
How to Use
- 1Paste raw HTTP response headers from your browser DevTools (Network tab), curl -I output, or any HTTP client.
- 2Headers are automatically categorized into groups: Cache, Security, CORS, Content, and Server.
- 3Review the Security section for warnings about missing security headers; each includes a severity level and explanation.
- 4Click on any header value to copy it, or use the Copy All button to copy the complete header list.
- 5Use curl -I https://example.com in a terminal to get headers for any public URL.
- 6Open browser DevTools (F12) → Network tab → reload the page → click a request to see its response headers.
- 7Use the live fetch feature by entering a URL directly and clicking Fetch; the tool makes a browser fetch request and displays all response headers automatically
- 8Check the Cache section to understand your site's caching policy; look for Cache-Control max-age values to see how aggressively content is cached by browsers and CDNs
Frequently Asked Questions
Why can't this tool fetch headers directly from a URL?
Browser CORS (Cross-Origin Resource Sharing) policies prevent JavaScript from making cross-origin requests and reading response headers unless the target server explicitly allows it via Access-Control-Allow-Origin headers. Since most websites don't include this header, a browser-based fetch tool cannot read response headers. The paste approach works universally with any URL.
How do I get raw HTTP headers from a URL?
Open your browser's DevTools (F12), go to the Network tab, reload the page, and click on any request to see its response headers. Alternatively, use curl -I https://example.com in a terminal, or use your browser's 'Copy as cURL' feature to get the full response.
Why is my site flagged for missing security headers?
Your site gets flagged whenever an essential security header is absent: Strict-Transport-Security (HSTS) for HTTPS enforcement, Content-Security-Policy (CSP) to prevent XSS, X-Frame-Options to prevent clickjacking, X-Content-Type-Options to prevent MIME sniffing, and Referrer-Policy for privacy control. The audit marks each missing header with a severity level so you know which to fix first.
What is HSTS and why is it important?
HTTP Strict-Transport-Security (HSTS) tells browsers to always connect to your site via HTTPS, even if the user types HTTP or clicks an http:// link. This prevents SSL stripping attacks. Without HSTS, users on insecure networks (like public WiFi) could be redirected to fake HTTP versions of your site.
What do cache headers tell me?
Cache headers (Cache-Control, Expires, ETag, Last-Modified) control how browsers and CDNs store and reuse responses. A high max-age means better performance but slower content updates. No-cache or no-store means the content is always fetched fresh. Understanding these helps optimize page load speed.
What is the difference between response status codes?
Status codes indicate the result of an HTTP request: 2xx (success), 3xx (redirect), 4xx (client error like 404 Not Found), 5xx (server error). The tool displays the status code and text from the HEAD response, giving you a quick health check for any URL.
Can this tool detect server technology from headers?
Yes. The Server header often reveals the web server software (nginx, Apache, Cloudflare, etc.), and the X-Powered-By header may reveal the backend framework (PHP, ASP.NET, Express). The tool categorizes these under the Server group for easy identification.
Why are request headers different from response headers?
Request headers travel from the client to the server (User-Agent, Accept, Authorization, Cookie). Response headers travel back from the server (Content-Type, Set-Cookie, Cache-Control, Server). The body is the actual payload (HTML, JSON, or a file) that the headers describe. Headers are always plain-text lines; the body can be any binary or text data.
What does a full set of HTTP response headers look like?
Run curl -I https://example.com in a terminal to see a real example: HTTP/2 200 on the status line, then one header per line (content-type: text/html, cache-control: max-age=3600, server: nginx, set-cookie: ...) Each line is name: value. Paste that output here and the tool categorizes every header and flags missing security headers.
What is Content-Security-Policy (CSP) and why does it matter?
CSP is a security header that controls which resources (scripts, styles, images, fonts) a browser is allowed to load on your page. A properly configured CSP prevents cross-site scripting (XSS) attacks by blocking inline scripts and restricting script sources to trusted domains. It can also limit form submission targets and frame embedding. Missing CSP is flagged as a high-severity warning by the tool because XSS remains one of the most common web vulnerabilities.
What can I learn from the CORS headers section?
CORS (Cross-Origin Resource Sharing) headers determine whether web pages from other domains can access your API or resources. Key headers include: Access-Control-Allow-Origin (which domains are allowed), Access-Control-Allow-Methods (which HTTP methods are permitted), and Access-Control-Allow-Headers (which custom headers can be sent). The tool categorizes these under the CORS group so you can quickly verify your API's cross-origin policy. A missing or overly permissive Access-Control-Allow-Origin: * on sensitive APIs can expose data to unauthorized third-party websites.
Why does my http headers viewer show different headers than the ones my server sends?
The viewer shows what your client actually received, not necessarily what your origin server sent. CDNs and reverse proxies (Cloudflare, nginx) can add headers like cf-ray, x-cache, or via, rewrite existing ones, and strip sensitive ones. Browser extensions and HTTPS upgrades can also change the response. To compare origin vs edge, check the server directly with curl -I on the origin IP while the viewer inspects the public response.
Why does this online http header viewer show no headers for some websites?
The live fetch runs from your browser, so CORS applies to every cross-origin request: if the target site does not send Access-Control-Allow-Origin allowing your origin, the browser blocks reading the response; you will see an error instead of headers. This is a browser restriction, not a server problem. Paste mode works for every URL: copy the headers from DevTools or curl -I and paste them here.