Headers & User-Agent

Every click on a short link arrives with a packet of metadata — HTTP headers. They are the source of everything link analytics knows about who clicked, from where and on what device.

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Definition

HTTP headers are key-value metadata fields transmitted with every HTTP request and response. Request headers — sent by the browser with every request — contain information about the client making the request: what software it is, what language it prefers, where it came from and what content types it accepts.

For URL shorteners, request headers are the primary raw data source for link analytics. Every data point in the analytics dashboard — device type, OS, browser, language, referrer source — originates from parsing request headers captured at the moment of the click.

The Key Headers for Link Analytics

User-Agent

The User-Agent header identifies the software making the request. For browser clicks, it is a structured string containing browser name and version, rendering engine, OS name and version, and device type signals.

User-Agent parsing produces the device type (mobile/desktop/tablet), OS (iOS, Android, Windows, macOS, Linux), OS version and browser (Chrome, Safari, Firefox, Edge, Samsung Internet) data seen in link analytics dashboards.

User-Agent strings are also the primary mechanism for bot click detection: known crawler and bot User-Agents (Googlebot, Facebookbot, etc.) are identified and filtered from human click counts.

Referer

The Referer header contains the URL of the page from which the visitor navigated. It is the source of traffic source data in link analytics — "came from Facebook", "came from Google", "came from yourblog.com/article". When no Referer is present (email apps, messaging apps, direct navigation), the click is classified as direct.

Accept-Language

The Accept-Language header specifies the visitor's preferred language(s), as configured in their browser. It is used as a proxy for locale and language preference. Useful for understanding the language makeup of an audience reached by a link — particularly relevant for multilingual campaigns where the language distribution of clicks may inform localisation decisions.

IP Address (Not a Header, But Related)

The connecting IP address is not transmitted in a header — it is implicit in the TCP connection. It is used for geographic lookup: the IP address is matched against a geo-IP database to determine the country of origin, then discarded in GDPR-compliant implementations. Only the derived country value is stored in click analytics — not the IP address itself.

User-Agent Client Hints: The Modern Replacement

Modern Chrome-based browsers are gradually replacing the full User-Agent string with User-Agent Client Hints — a more structured, privacy-preserving mechanism that provides device and browser information in structured header fields rather than a single long string. The transition affects how detailed device analytics can be in future implementations, but the core data — device type, OS, browser — remains available.

Related Terms

• Click Tracking
• Referrers
• Traffic Sources
• Bot Click Detection
• GDPR & Analytics