HTTP Headers Viewer
The HTTP Headers Viewer fetches HTTP requests and displays comprehensive request and response headers from web servers, APIs, or…
HTTP Headers Viewer
Enter a URL to fetch HTTP headers
HTTP Headers
Request Headers
Response Headers
Headers Analysis
Security Headers
Performance Headers
About HTTP Headers
Common Request Headers:
- • User-Agent: Client application info
- • Accept: Accepted content types
- • Authorization: Authentication credentials
- • Referer: Referring page URL
- • Cache-Control: Caching directives
Common Response Headers:
- • Content-Type: Resource media type
- • Content-Length: Response body length
- • Server: Server software info
- • Set-Cookie: HTTP cookies
- • Cache-Control: Caching directives
Security Headers Checklist
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Learn more — open a section when you need details
The HTTP Headers Viewer fetches HTTP requests and displays comprehensive request and response headers from web servers, APIs, or endpoints, highlighting critical security and performance directives with color-coded indicators and detailed analysis. It supports multiple HTTP methods (GET, HEAD, POST, OPTIONS) for different testing scenarios, allows adding custom headers like Authorization tokens or custom User-Agent strings, and provides intelligent analysis that checks for essential security protections including Content Security Policy (CSP), HTTP Strict Transport Security (HSTS), X-Frame-Options for clickjacking protection, and other security headers. The tool summarizes response metadata including HTTP status codes, response time measurements, content length, header counts, and provides a comprehensive security checklist identifying missing or misconfigured headers. All header fetching and analysis happens entirely in your browser using JavaScript Fetch API, ensuring complete privacy. Perfect for troubleshooting API endpoints by verifying CORS configuration and authentication headers, conducting security reviews to verify security headers on production websites, performance tuning by checking compression and cache directives, or documenting HTTP header configurations for compliance audits, change tracking, and security reporting.
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Enter a target URL in the URL input field and select the appropriate HTTP method from the dropdown: GET for standard requests, HEAD for header-only checks (faster, no body transfer), POST for form submissions, or OPTIONS for CORS preflight testing.
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Optionally add custom request headers using the custom headers section, such as Authorization tokens (Bearer tokens, API keys), custom User-Agent strings, Accept headers, or any other headers required for your specific API endpoint or testing scenario.
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Click the Fetch Headers button to send the HTTP request and populate both the Request Headers section (showing headers you sent) and Response Headers section (showing headers returned by the server), displaying all headers in a readable key-value format.
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Review the response summary showing HTTP status code (200, 404, 500, etc.), response time in milliseconds, content length, total header count, and any redirect information if the server returns redirect responses (3xx status codes).
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Click the Analyze Headers button to run comprehensive security and performance analysis, checking for essential security headers (CSP, HSTS, X-Frame-Options, etc.), performance headers (compression, caching), and generating a detailed checklist of header coverage and recommendations.
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Examine the security checklist panel highlighting which security headers are present, missing, or misconfigured, with recommendations for improving security posture by adding or correcting security headers on your server configuration.
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Copy individual headers or the complete header analysis to clipboard, or use the Export feature to download header analysis results as JSON format for sharing with team members, storing in CI/CD artifacts, or including in security audit documentation.
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Test different HTTP methods (HEAD vs GET) to compare header responses, verify CORS preflight behavior with OPTIONS method, or test custom header combinations to understand how servers respond to different request configurations for API integration or security testing.
Security header auditing and compliance verification
Verify Content Security Policy (CSP), HTTP Strict Transport Security (HSTS), X-Frame-Options, and other critical security headers on production websites, identifying missing security protections that could expose sites to XSS attacks, clickjacking, or man-in-the-middle vulnerabilities, ensuring compliance with security best practices and regulatory requirements.
API endpoint debugging and CORS testing
Confirm CORS (Cross-Origin Resource Sharing) configuration by checking Access-Control-Allow-Origin, Access-Control-Allow-Methods, and related CORS headers on API endpoints, debugging cross-origin request failures, verifying authentication headers work correctly, and ensuring API endpoints respond with proper headers for client-side integration.
Performance optimization and cache analysis
Check compression headers (Content-Encoding: gzip), cache directives (Cache-Control, ETag, Last-Modified), and content delivery headers after server configuration changes, verifying that performance optimizations are properly configured and identifying opportunities to improve response times through better caching or compression settings.
HTTP header documentation and change tracking
Export HTTP headers as JSON documentation for API specifications, security audit trails, or compliance reports, creating baseline header configurations for tracking changes over time, documenting server configurations, or sharing header requirements with development teams for consistent implementation across services.
Server configuration verification and troubleshooting
Verify that server configuration changes (nginx, Apache, or application server settings) result in expected HTTP headers, troubleshoot header-related issues like missing security headers after deployment, or validate that reverse proxies or CDNs preserve or modify headers correctly in production environments.
Security penetration testing and vulnerability assessment
Identify security vulnerabilities by analyzing missing security headers, misconfigured CORS policies, or information leakage through headers like Server, X-Powered-By, or X-AspNet-Version that reveal technology stack details to attackers, enabling security teams to assess and improve application security posture.
Development and staging environment testing
Compare headers between development, staging, and production environments to ensure consistent security configurations, verify that security headers are properly deployed across all environments, and catch header misconfigurations before they reach production by testing in lower environments.
Third-party API integration and header verification
Inspect headers from third-party APIs or services to understand their response structure, verify authentication mechanisms (token validation, API key handling), check rate limiting headers, or understand content negotiation headers for proper API integration and error handling in applications consuming external APIs.
Prefer HEAD method when you only need headers without response body content, as HEAD requests are faster, use less bandwidth, and return the same headers as GET requests but without downloading response body, making them ideal for quick header checks or status verification without unnecessary data transfer.
Implement a strict Content Security Policy (CSP) and enable HTTP Strict Transport Security (HSTS) in production environments, as these headers provide critical protection against XSS attacks, data injection, and man-in-the-middle attacks by controlling resource loading and enforcing HTTPS connections for improved security posture.
Enable response compression (gzip, brotli) and set proper cache policies using Cache-Control headers with appropriate max-age values and immutability flags for static assets, reducing bandwidth usage, improving page load times, and providing better user experience through efficient content delivery.
Hide server technology fingerprints by removing or minimizing Server, X-Powered-By, or X-AspNet-Version headers that reveal technology stack details to attackers, as information leakage through headers can help attackers identify known vulnerabilities or choose targeted attack vectors against specific technologies.
Validate headers across both HTTP and HTTPS variants of your website, as some headers behave differently or are only applicable to HTTPS (like HSTS), and ensure consistent security configuration across both protocols to prevent security gaps or mixed-content issues in applications.
Check CORS headers carefully for API endpoints, ensuring Access-Control-Allow-Origin is not set to wildcard (*) for sensitive APIs, as overly permissive CORS policies can allow unauthorized cross-origin access and create security vulnerabilities, especially for APIs handling authentication or sensitive data.
Review cache headers for both static assets and dynamic content, using long-lived caching (max-age) for immutable static assets but appropriate cache control (no-cache, must-revalidate) for dynamic content that changes frequently or contains sensitive information requiring fresh data delivery.
Document expected headers and create header baselines for your applications, making it easier to detect configuration drifts, verify deployment correctness, or troubleshoot header-related issues by comparing current headers against documented expected configurations and identifying unexpected changes or missing headers.
Missing HTTP Strict Transport Security (HSTS) headers on HTTPS sites, weakening TLS enforcement and leaving sites vulnerable to protocol downgrade attacks or man-in-the-middle attacks, when HSTS headers should always be present on HTTPS websites to force secure connections and prevent insecure HTTP fallbacks.
Configuring overly permissive CORS policies allowing any origin (*) for sensitive APIs or endpoints handling authentication or user data, creating security vulnerabilities where malicious websites can make unauthorized cross-origin requests to your APIs and access sensitive information or perform unauthorized actions.
Leaking technology stack information through Server, X-Powered-By, X-AspNet-Version, or similar headers that reveal server software, framework versions, or technology details to attackers, enabling targeted attacks against known vulnerabilities in specific technologies or helping attackers choose appropriate exploitation techniques.
Using no-cache or no-store directives for long-lived static assets (images, CSS, JavaScript) where long-lived caching is safe and beneficial, missing opportunities to improve performance through browser caching, increasing server load unnecessarily, and reducing user experience with slower page loads due to repeated asset downloads.
Not setting Content Security Policy (CSP) headers on production websites, leaving applications vulnerable to XSS attacks, data injection attacks, or code injection vulnerabilities, when CSP headers provide critical protection by controlling which resources can be loaded and executed by browsers.
Ignoring security header recommendations or missing essential headers like X-Content-Type-Options, X-Frame-Options, or Referrer-Policy, creating security gaps that expose applications to MIME type sniffing attacks, clickjacking, or referrer information leakage that could compromise user privacy or enable attacks.
Testing headers only in development or staging environments without verifying production configurations, when header configurations can differ between environments due to different server software, reverse proxies, CDNs, or application server settings, potentially missing security issues that only exist in production.
Not documenting or tracking header changes over time, making it difficult to identify when security headers were removed, modified, or when configuration changes introduced security regressions, as header configurations can change during deployments, server updates, or configuration management changes.
Assuming all headers work identically across different browsers or HTTP clients, when some headers have browser-specific behavior, support variations, or interpretation differences that could cause compatibility issues or security gaps in certain browser environments or client implementations.
Using GET method for header-only checks instead of HEAD method, unnecessarily downloading response bodies when only headers are needed, wasting bandwidth, increasing response times, and potentially exposing sensitive data in response bodies when header analysis alone would suffice for testing or verification purposes.
Not testing CORS preflight requests (OPTIONS method) separately from actual requests, missing CORS configuration issues that only appear during preflight, as CORS involves both preflight OPTIONS requests and actual requests, and both must be properly configured for cross-origin access to work correctly.
Exporting or sharing header analysis results containing sensitive information like authentication tokens, API keys, or session identifiers without sanitizing headers first, potentially exposing credentials or sensitive data in documentation, audit reports, or shared analysis results that could be used maliciously if accessed by unauthorized parties.
The tool fetches headers using browser JavaScript Fetch API, which means requests are made from your browser to the target URL you specify. URLs are sent to target servers (which is necessary to fetch headers), but header analysis and processing happens locally. For sensitive URLs, ensure you trust the target server. The tool itself does not log or store URLs on intermediate servers.
HEAD method returns only HTTP headers without response body, making it faster and using less bandwidth—ideal when you only need headers. GET method returns both headers and response body, useful when you need to see full responses. For header analysis, prefer HEAD to avoid unnecessary data transfer, but use GET if you need to verify headers work with actual request handling.
Test CORS using OPTIONS method for preflight requests, then check Access-Control-Allow-Origin, Access-Control-Allow-Methods, Access-Control-Allow-Headers, and Access-Control-Allow-Credentials headers. Verify preflight (OPTIONS) and actual (GET/POST) requests both return appropriate CORS headers, as CORS requires proper configuration for both request types. Also test from different origins to verify CORS policies work as intended.
Prefer Cache-Control headers with max-age values for static assets (long cache for immutable resources), immutability flags for versioned assets, and appropriate validation headers (ETag, Last-Modified). Use no-cache or must-revalidate for dynamic content. Combine Cache-Control with ETag/Last-Modified for efficient validation, allowing browsers to verify freshness without full downloads, improving performance while ensuring content accuracy.
Essential security headers include: Content-Security-Policy (CSP) for XSS protection, HTTP Strict Transport Security (HSTS) for HTTPS enforcement on HTTPS sites, X-Frame-Options for clickjacking protection, X-Content-Type-Options: nosniff to prevent MIME sniffing, and Referrer-Policy to control referrer information. Additional headers like Permissions-Policy and X-XSS-Protection provide additional layers of security depending on your application needs.
Common causes include: reverse proxies or CDNs stripping headers, application server not passing headers through, HTTPS-only headers (like HSTS) not appearing on HTTP requests, server configuration syntax errors, or middleware removing headers. Verify server configuration syntax, check reverse proxy/CDN settings, test directly against application server, and ensure headers are set for the correct protocol (HTTP vs HTTPS).
Yes, use the custom headers section to add Authorization headers (Bearer tokens, API keys), custom authentication headers, or any required headers for your API endpoints. Add headers like "Authorization: Bearer your-token" or "X-API-Key: your-key" to test protected endpoints and verify that authentication headers are properly handled and that protected resources return appropriate responses.
The security checklist analyzes headers and flags missing or misconfigured security headers. Green indicators show headers are present and properly configured, yellow indicates headers are present but may need optimization, and red indicates missing critical security headers. Review recommendations for each flagged item, prioritize critical security headers (CSP, HSTS), and implement recommended header configurations based on your application security requirements.
Cache-Control is the modern, preferred method with more control (max-age, must-revalidate, no-cache directives), while Expires provides absolute expiration dates. Cache-Control takes precedence when both are present. Prefer Cache-Control with max-age for relative expiration times that are easier to manage, though supporting both provides backward compatibility with older caching implementations that only understand Expires headers.
Use the Export feature to download header analysis as JSON format, which includes all request/response headers, security checklist results, and metadata (status code, response time, etc.). This JSON can be included in security audit documentation, API specifications, compliance reports, or stored in version control for tracking header changes over time and demonstrating security configuration compliance to auditors or stakeholders.
Headers can vary due to: CDN edge servers adding/modifying headers, reverse proxies inserting headers, browser-specific header handling, geographic location affecting CDN behavior, or server-side logic that modifies headers based on request characteristics. Test from multiple locations and browsers to understand header variations, and verify that security headers are consistently present regardless of request origin or client.
CORS errors typically indicate missing or incorrect Access-Control-Allow-Origin headers. Fix by: configuring server to return appropriate Access-Control-Allow-Origin (specific origin, not * for sensitive APIs), adding required CORS headers (Access-Control-Allow-Methods, Access-Control-Allow-Headers), ensuring OPTIONS preflight requests return correct CORS headers, and verifying credentials handling if using Access-Control-Allow-Credentials. Test with actual cross-origin requests to verify fixes work correctly.