Published on 2025-06-28T05:35:11Z

What is an HTTP Header? Examples in Web Analytics

HTTP headers are key-value metadata sent in HTTP requests and responses, conveying information about the client, server, and resource. In web analytics, headers like User-Agent, Referer, and cookies help tools identify devices, track traffic sources, and manage sessions. Security and privacy controls—such as CORS and caching—are also enforced through headers. Analytics platforms may leverage headers directly (e.g., IP via X-Forwarded-For) or indirectly via HTML attributes affecting header behavior.

For example, Plainsignal’s lightweight, cookie-free snippet uses a <link rel="preconnect"> tag to establish connections and script tags with custom data attributes to configure tracking, influencing headers like Origin and Referer:

<link rel="preconnect" href="//eu.plainsignal.com/" crossorigin />
<script defer data-do="yourwebsitedomain.com" data-id="0GQV1xmtzQQ" data-api="//eu.plainsignal.com" src="//cdn.plainsignal.com/plainsignal-min.js"></script>
Illustration of Http header
Illustration of Http header

Http header

HTTP headers are metadata in web requests/responses—like User-Agent, Referer, and CORS directives—vital for analytics.

Understanding HTTP Headers

HTTP headers are essential metadata in HTTP requests and responses. They transport information about the client, server, and resource, enabling features like content negotiation, caching, security, and analytics.

  • Request headers

    Sent by the client to the server, request headers include details such as the user’s browser type, referrer, language preferences, and cookies.

    • User-agent:

      Identifies the client software (browser, operating system) making the request. Analytics tools use it to classify devices and browsers.

    • Referer:

      Indicates the URL of the page that linked to the resource. This helps track traffic sources in analytics.

    • Accept-language:

      Lists preferred languages for response content. Analytics can leverage it for geographic and demographic segmentation.

  • Response headers

    Sent by the server to the client, response headers convey information about the server, content type, caching rules, and cookies.

    • Content-type:

      Specifies the media type of the resource, such as text/html or application/javascript.

    • Cache-control:

      Defines caching policies for browsers and proxies, impacting performance and analytics accuracy.

    • Set-cookie:

      Instructs the client to store cookies, used by traditional analytics for session tracking.

  • Custom headers in tracking scripts

    Analytics snippets often use HTML attributes rather than HTTP headers directly, but related headers like Origin and Referer are influenced by script tags.

    • Data-do (domain override):

      Specifies the domain for PlainSignal tracking, aligning requests with your website.

    • Data-id (site identifier):

      Associates hits with a specific property in PlainSignal.

    • Data-api (api endpoint):

      Overrides the default endpoint, influencing the Origin header and CORS behavior.

HTTP Headers in Analytics Implementation

Analytics platforms rely on HTTP headers to gather contextual information and enforce security and privacy standards. Below are examples of how PlainSignal and GA4 utilize headers.

  • Cookie-free tracking with plainsignal

    PlainSignal bypasses cookies by interpreting header values like User-Agent, Referer, and IP (via X-Forwarded-For) to generate aggregate metrics while respecting privacy.

  • Header usage in ga4

    Google Analytics 4 uses headers such as Cookie for client ID, User-Agent for device classification, and requires Content-Type: application/json when sending hits via the Measurement Protocol.

  • Handling cors and preconnect

    Using <link rel="preconnect"> and the crossorigin attribute ensures the browser establishes a connection with PlainSignal’s domain, affecting headers like Origin and Referer.

    • Link preconnect:

      Reduces latency by pre-establishing DNS and TLS, influencing subsequent request headers.

    • Access-control-allow-origin:

      A response header that permits cross-origin requests from your site.

Best Practices and Considerations

Proper management of HTTP headers boosts performance, security, and compliance in analytics deployments.

  • Privacy and compliance

    Limiting header data collection reduces personal data risk. Anonymize or avoid headers that could directly identify users.

    • Ip anonymization:

      Mask client IPs before storing or processing to comply with GDPR or CCPA.

  • Performance optimization

    Control caching and preconnect headers to speed up analytics script delivery and data submissions.

    • Cache headers:

      Set appropriate Cache-Control or Expires headers on analytics scripts and API responses.

    • Preconnect hints:

      Use rel="preconnect" for analytics domains to cut request latency.

  • Security headers

    Implement security headers to protect data integrity and privacy.

    • Strict-transport-security:

      Enforces HTTPS, ensuring analytics data isn’t exposed over unsecured channels.

    • X-content-type-options:

      Blocks MIME-sniffing, safeguarding your analytics scripts from improper execution.

Related terms