The Complete Glossary of Server-Side Tracking Terms

The Language of Server-Side Tracking

Server-side tracking has a vocabulary that combines web analytics terminology with cloud infrastructure and API concepts. This glossary defines the key terms used in server-side tracking discussions and documentation.

Core Architecture Terms

Client-Side Tracking: tracking that runs in the user's browser via JavaScript tags. Events are sent directly from the browser to analytics platforms. Affected by ad blockers and browser privacy restrictions.

Server-Side Tracking: tracking where events are processed on a server you control before being forwarded to analytics platforms. Bypasses browser restrictions by routing through a first-party server.

Tagging Server: the server that receives events from your website, processes them, and forwards them to analytics platforms. In the sGTM context, this is the server running the Google Tag Manager server container.

sGTM (Server-Side Google Tag Manager): Google's open-source server application that can be self-hosted on cloud infrastructure. Uses the familiar GTM interface for configuration. Also called Server GTM or Server Container.

Server Container: a GTM container created specifically for server-side use. Contains clients, tags, triggers, and variables that run on the tagging server instead of in the browser.

Web Container: a standard GTM container that runs in the user's browser. Distinguished from the server container.

Custom Domain / First-Party Domain: a subdomain of your own domain (e.g. collect.yoursite.com) that hosts your tagging server. Essential for ad blocker resistance and first-party cookie setting.

sGTM-Specific Terms

Client (sGTM Component): a component in the server container that receives and parses incoming requests. The GA4 client parses GA4-format events. A custom client can parse webhook or custom payloads.

Claim: when an sGTM client "claims" an incoming request, it takes ownership of processing it. Only one client can claim a request — other clients that would also match are skipped.

runContainer: the function called by an sGTM client to trigger tag firing in the server container after claiming and parsing a request.

Event Data: the structured object representing an event in the server container. Populated by the client from the incoming request and made available to tags and variables.

Data and Protocol Terms

Measurement Protocol: Google Analytics' HTTP API for sending events directly from servers to GA4. Used by sGTM to forward events to Google Analytics.

CAPI (Conversions API): Meta's server-to-server API for sending conversion events. Also used generically for other platforms' server-side conversion APIs (TikTok CAPI, LinkedIn CAPI, Pinterest CAPI).

Event Match Quality (EMQ): Meta's score (0-10) for how well it can match a CAPI event to a specific user in its system. Higher EMQ = better attribution. Improved by including hashed customer identifiers (email, phone, IP, fbp, fbc).

Webhook: an HTTP request sent automatically by a third-party system to your server when an event occurs. Stripe sends webhooks for payments. Shopify sends webhooks for orders. Used to capture backend conversion events server-side.

Measurement Protocol API Secret: a credential required to send events to GA4 via the Measurement Protocol. Created in GA4's Data Stream settings.

Container Config: the URL provided by GTM when creating a server container. Used to connect a deployed tagging server instance to the GTM server container configuration.

Privacy and Cookie Terms

ITP (Intelligent Tracking Prevention): Safari's privacy feature that limits cookie lifetimes and blocks cross-site tracking. The primary driver for server-side first-party cookie setting.

First-Party Cookie: a cookie set by the same domain the user is visiting. When set via HTTP Set-Cookie header from your own server/subdomain, it is not subject to ITP's 7-day JavaScript cookie cap.

Set-Cookie Header: the HTTP response header used to set cookies server-side. Cookies set this way bypass ITP's JavaScript cookie restrictions.

_ga Cookie: the GA4 user identification cookie. When set by the GA4 JavaScript library, it is subject to ITP's 7-day cap. When set server-side via sGTM, it can have a 2-year lifetime.

_fbp Cookie: the Meta browser ID cookie set by the Meta Pixel. Passed to CAPI for better Event Match Quality.

_fbc Cookie: the Meta click ID cookie, set when a user arrives from a Facebook ad with fbclid in the URL.

Attribution Terms

GCLID (Google Click ID): the unique identifier appended to landing page URLs when a user clicks a Google Ad. Used to attribute conversions to specific ad clicks.

Client ID: GA4's unique identifier for a user's browser instance, stored in the _ga cookie. Used to link events across sessions in GA4.

Offline Conversion: a conversion event reported after-the-fact via API, rather than in real-time via a browser tag. Used for sales confirmed by CRM, phone calls, or server-side events.

Summary

Understanding these terms is the foundation for working effectively with server-side tracking documentation, configuration, and troubleshooting. Return to this glossary whenever a new term appears in your sGTM setup or debugging sessions.

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