HTTP Headers

HTTP headers are an essential part of the HTTP protocol, providing important metadata about the request or response. They contain information about the server, caching policies, security settings, content type, and more. Understanding and properly configuring HTTP headers is crucial for web security, performance, and functionality.

HTTP Headers Tool

Our HTTP Headers tool helps you analyze HTTP response headers to understand server configurations, security policies, and caching directives.

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What are HTTP Headers?

HTTP headers are key-value pairs that are sent at the beginning of an HTTP response or request. They define the operating parameters of an HTTP transaction and provide important information about the server, the client, and the requested resource.

Headers are divided into two main categories:

Request Headers

Sent by the client (browser) to the server, providing information about the request and the client itself.

Examples include:

User-Agent: Information about the browser and operating system
Accept: Content types the client can process
Cookie: Stored cookies for the domain
Authorization: Authentication credentials

Response Headers

Sent by the server to the client, providing information about the server and the resource being returned.

Examples include:

Content-Type: The MIME type of the returned content
Server: Information about the server software
Set-Cookie: Cookies to be stored by the client
Cache-Control: Directives for caching mechanisms

Important HTTP Headers

HTTP headers can be categorized based on their purpose:

Security Headers

These headers help protect against various web vulnerabilities and attacks:

Content-Security-Policy: Controls which resources the browser is allowed to load
Strict-Transport-Security: Forces browsers to use HTTPS for the domain
X-XSS-Protection: Enables browser's built-in XSS filtering
X-Content-Type-Options: Prevents MIME type sniffing
X-Frame-Options: Controls whether a page can be displayed in frames
Referrer-Policy: Controls how much referrer information is included with requests
Permissions-Policy: Controls which browser features can be used

Caching Headers

These headers control how responses are cached:

Cache-Control: Directives for caching mechanisms
ETag: Unique identifier for a specific version of a resource
Last-Modified: Date and time the resource was last modified
Expires: Date/time after which the response is considered stale
Vary: Specifies which request headers influence the caching

Content Headers

These headers provide information about the content being transferred:

Content-Type: The MIME type of the content
Content-Length: The size of the content in bytes
Content-Encoding: The encoding used on the content (e.g., gzip)
Content-Language: The language of the content
Content-Disposition: Indicates if content should be displayed inline or as an attachment

CORS Headers

These headers control Cross-Origin Resource Sharing:

Access-Control-Allow-Origin: Which origins can access the resource
Access-Control-Allow-Methods: HTTP methods allowed when accessing the resource
Access-Control-Allow-Headers: Headers that can be used in the actual request
Access-Control-Allow-Credentials: Whether request can include credentials
Access-Control-Max-Age: How long preflight results can be cached

HTTP Header Examples

Here's an example of HTTP response headers from a secure website:

HTTP/2 200 OK
date: Wed, 05 Mar 2025 12:34:56 GMT
content-type: text/html; charset=UTF-8
strict-transport-security: max-age=31536000; includeSubDomains; preload
content-security-policy: default-src 'self'; script-src 'self' https://trusted-cdn.com
x-content-type-options: nosniff
x-frame-options: DENY
x-xss-protection: 1; mode=block
referrer-policy: strict-origin-when-cross-origin
permissions-policy: camera=(), microphone=(), geolocation=()
cache-control: max-age=3600, must-revalidate
etag: "33a64df551425fcc55e4d42a148795d9f25f89d4"
content-encoding: gzip
server: nginx
vary: Accept-Encoding
access-control-allow-origin: https://example.com

This example shows a well-configured set of headers that implement security best practices, proper caching, and content information.

Common HTTP Header Issues

Missing Security Headers

Many websites lack important security headers like Content-Security-Policy, which can leave them vulnerable to various attacks such as XSS, clickjacking, and data injection.

Improper CORS Configuration

Setting Access-Control-Allow-Origin to "*" or improperly configuring CORS headers can expose your API to unauthorized cross-origin requests.

Inefficient Caching

Incorrect Cache-Control directives can lead to either excessive server requests (if caching is too restrictive) or serving stale content (if caching is too permissive).

Information Disclosure

Headers like Server, X-Powered-By, or X-AspNet-Version can reveal too much information about your technology stack, making it easier for attackers to target known vulnerabilities.

Inconsistent Content Types

Serving content with incorrect Content-Type headers can cause browsers to misinterpret the content, potentially leading to security issues or rendering problems.

HTTP Header Best Practices

Implement Security Headers

Always include essential security headers like Content-Security-Policy, Strict-Transport-Security, X-Content-Type-Options, and X-Frame-Options to protect against common web vulnerabilities.

Configure Proper Caching

Use appropriate Cache-Control directives based on content type. Static assets can be cached longer, while dynamic content might need shorter cache times or no caching at all.

Restrict CORS Appropriately

Only allow specific trusted origins in your Access-Control-Allow-Origin header rather than using the wildcard "*", especially for APIs that handle sensitive data.

Minimize Information Disclosure

Avoid exposing detailed server information in headers. Consider removing or customizing headers like Server and X-Powered-By.

Use Correct Content Types

Always specify the correct Content-Type header for the content being served to ensure proper rendering and interpretation by browsers.

Enable Compression

Use Content-Encoding headers with compression methods like gzip or brotli to reduce bandwidth usage and improve loading times.

Regularly Audit Headers

Periodically check your HTTP headers to ensure they remain properly configured and up-to-date with current security best practices.

Our HTTP Headers Tool

Our HTTP Headers tool allows you to analyze the HTTP response headers of any website. It provides:

A complete list of all HTTP response headers
Security header analysis and recommendations
Caching header analysis
CORS configuration assessment
Server information
Content information
Performance suggestions based on header configuration

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Interpreting HTTP Headers Analysis Results

Our HTTP Headers tool provides a comprehensive analysis with issues categorized by severity:

Critical Issues

High-severity security issues that should be addressed immediately, such as missing essential security headers or dangerous CORS configurations.

Warnings

Medium-severity issues that should be addressed to improve security or performance, such as suboptimal caching configurations or information disclosure.

Recommendations

Suggestions for improving your header configuration based on best practices, such as enabling compression or adding additional security headers.

Passed Checks

Headers that are properly configured according to best practices.

Pro Tip

When implementing Content-Security-Policy, start with a report-only policy (Content-Security-Policy-Report-Only) to identify potential issues before enforcing restrictions. This allows you to collect violation reports without breaking functionality.

Next Steps

To further enhance your website's security and performance, consider exploring these related tools and resources:

SSL Certificate Checker - Verify SSL certificates and encryption
DNS Security Scan - Check your domain's DNS security
Ping Tool - Test network connectivity and response times
Web Security Best Practices - Comprehensive guide to securing your website

Ready to analyze your website's HTTP headers? Use our HTTP Headers Tool now.