01
Page URL
Returns the address of the current page. A variable is a named value: GTM can ask for Page URL at the moment it needs it, then use that value in a condition, trigger, or tag.
CONCEPTVariable · value · string
MICHAEL CASTRO / GUIDE
Understand the
Starter Kit.
The Starter Kit is not a pile of tags. It is a small vocabulary for describing what happened on a website. Start with primitive values, then watch them compose into reusable measurement logic.
HOW TO READ THE SYSTEM
VARIABLESWhat value do we know?
→TRIGGERSWhen is a condition true?
→TAGSWhat should happen?
STARTER KIT REFERENCE
Primitive first.
Composition second.
Each section expands the Note included inside GTM and introduces the underlying web or computer-science idea only where it makes the implementation easier to understand.
02
Page Hostname
Returns the hostname of the current page, such as example.com. It is a smaller, more specific piece of the full URL and is useful when logic depends on the site or subdomain rather than the entire address.
CONCEPTData decomposition · string
03
Page Path
Returns the path portion of the current URL, such as /pricing. Separating a URL into parts lets measurement logic describe intent more cleanly: Page Path contains /pricing is easier to reason about than matching a complete URL.
CONCEPTComposition · conditions
04
Referrer
Returns the referring URL available to the browser. A referrer is context: it describes where the current page navigation came from. The Starter Kit later derives Referrer Hostname from this more primitive value.
CONCEPTInput · derived value
05
Event
Returns the name of the current GTM event. GTM is event-driven: instead of running one linear program from beginning to end, it reacts as page loads, clicks and other interactions occur.
CONCEPTEvent-driven programming
06
Click Element
Returns the actual HTML element associated with a click. Unlike a text value, this is an object representing part of the page’s Document Object Model. More advanced Starter Kit components can inspect it and move through its relationships.
CONCEPTObject · DOM · state
07
Click URL
Returns the destination URL associated with a clicked link. Other Starter Kit components derive the hostname, path and file extension from this value instead of repeatedly solving the same problem.
CONCEPTReuse · derived values
08
Click Text
Returns text associated with a click. It can be useful context, but the exact clicked node is not always the element a person conceptually interacted with. That limitation motivates the later Closest Interactive Element and Interaction Label Starter Kit components.
CONCEPTAbstraction · edge cases
09
Google Analytics Measurement ID (G-0000000)
Stores one reusable value for the Google Analytics Measurement ID. A constant is a value intended to stay the same while the container runs. The included G-0000000 value is deliberately a placeholder and must be replaced before publishing.
CONCEPTConstant · single source of truth
10
Click Hostname
Returns only the hostname of Click URL, such as example.com, with www removed. This is a derived variable: it takes a more general input and transforms it into the specific value needed for classification and conditions.
CONCEPTFunction-like transformation · return value
11
Click Path
Returns only the path of Click URL, such as /pricing. It demonstrates a useful programming pattern: normalize complex input into smaller values that can be compared reliably.
CONCEPTNormalization · comparison
12
Click File Extension
Returns the filename extension from Click URL, such as pdf or xlsx. The File Download Click trigger later uses this returned value as an input to a condition.
CONCEPTReturn value · dependency
13
Referrer Hostname
Returns only the hostname from Referrer. This is another example of composition: a primitive browser value becomes a more useful Starter Kit component without changing the original value.
CONCEPTComposition · immutability
14
Element Type
Returns the HTML element type involved in an interaction, such as BUTTON, SPAN, INPUT, or A. HTML elements are the structural objects that make up a web page; their type is one clue to what an interaction means.
CONCEPTDOM · type
15
Element ID
Returns the id attribute of the clicked HTML element. An ID is intended to identify a particular element in a document, making it useful when a site provides stable, meaningful IDs.
CONCEPTIdentifier · attribute
16
Element Attribute — ARIA Label
Returns the aria-label attribute. ARIA labels provide accessible names for controls that may not have useful visible text, so they can also provide meaningful interaction context when used carefully.
CONCEPTAttribute · accessibility semantics
17
Closest Interactive Element
Starts with Click Element and asks the browser for the nearest link, button, form control, or common ARIA control. This solves a common DOM problem: a person clicks an icon or span nested inside the button they actually meant to activate.
CONCEPTFunction · DOM traversal · ancestor relationship
18
Interaction Label
Returns the best available human-readable label for Closest Interactive Element. It checks sources in a deliberate order—accessibility label, normalized visible text, then descriptive attributes—and returns the first useful value. Input values are intentionally excluded as a privacy safeguard.
CONCEPTFunction · precedence · fallback · return value
19
Interaction Type
Describes the resolved interactive element using its role, type attribute, or HTML tag. This is an abstraction layer: downstream logic can ask what kind of interaction occurred without repeating the DOM inspection.
CONCEPTAbstraction · encapsulation
20
Is Interactive Non-Link?
Returns true when the resolved interactive element is interactive but is not a standard or ARIA link. A Boolean has only two values—true or false—which makes it ideal for trigger conditions. The question-style name is intentional: “Is Interactive Non-Link? equals true” reads like a sentence.
CONCEPTBoolean · predicate · condition
21
Is External Link?
Compares the clicked link hostname with the current page hostname and returns true when they differ, treating www and non-www as the same host. It turns several operations into one reusable yes-or-no question.
CONCEPTBoolean · normalization · comparison
22
Link Click
Listens for link clicks and provides a reusable base trigger. A trigger is a condition for execution: it answers when a tag should be allowed to run. Duplicate this base and add conditions instead of rebuilding link-click logic each time.
CONCEPTEvent listener · condition · reuse
23
Interactive Non-Link Click
Fires when Is Interactive Non-Link? equals true. This shows how Starter Kit components compose: the trigger does not need to understand the DOM because the Boolean variable has already reduced that complexity to true or false.
CONCEPTComposition · predicate
24
External Link Click
Fires when Is External Link? equals true. Duplicate it and add Page Path or Click Hostname conditions when the business question requires a narrower definition.
CONCEPTComposition · logical conditions
25
File Download Click
Uses Click File Extension and a regular-expression pattern to recognize common downloadable files. A regular expression is a compact language for matching text patterns. Google Analytics Enhanced Measurement may already collect file_download, so check before attaching another GA4 file-download tag.
CONCEPTRegular expression · pattern matching · duplication
26
Google Tag Event Settings
Composes Environment Name, Container ID and Container Version into one gtm_context value. This demonstrates why small Starter Kit components matter: simple primitive values can be assembled into richer diagnostic context without hard-coding it into every tag.
CONCEPTComposition · observability
27
Google Tag
Uses the Measurement ID and shared Event Settings to load Google Analytics. Tags are outputs/actions in GTM: variables supply values, triggers decide when, and the tag performs the work. The Starter Kit deliberately fires it on Initialization and leaves the Measurement ID as a safe placeholder.
CONCEPTInputs → condition → action
THE PATTERN
Small pieces.
Legible systems.
The goal is not to make every GTM user a JavaScript developer. It is to make the logic visible enough that a marketer can understand what a system knows, why a condition is true, and what happens next.