Google Analytics 4 by Get MCP Ads

ga4 get custom definitions

ga4_get_custom_definitions

Read-onlyIdempotent

List custom dimensions and custom metrics from GA4 metadata to inventory available definitions. Use as a read-only fallback for checking what custom definitions a property exposes.

Instructions

List custom dimensions and custom metrics exposed by GA4 Data API metadata. Read-only fallback for custom definition inventory.

Input Schema

Name	Required	Description	Default
`propertyId`	Yes	GA4 property ID (numeric, e.g., 123456789)

Output Schema

Name	Required	Description	Default
`result`	Yes	Original tool result: parsed JSON when the text is JSON, otherwise the text or multiple MCP content blocks. Provider fields depend on the selected query.

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedv2.1.1Oct 30, 2026

removedInput schema / additionalProperties
```
Removed value: -false
```

changedOutput schema / properties / result / anyOf

Previous value: -[
-  {
-    "additionalProperties": true,
-    "properties": {},
-    "type": "object"
-  },
-  {
-    "items": {},
-    "type": "array"
-  },
-  {
-    "type": "string"
-  },
-  {
-    "type": "number"
-  },
-  {
-    "type": "boolean"
-  },
-  {
-    "type": "null"
-  }
-]New value: +[
+  {
+    "additionalProperties": {},
+    "properties": {},
+    "type": "object"
+  },
+  {
+    "items": {},
+    "type": "array"
+  },
+  {
+    "type": "string"
+  },
+  {
+    "type": "number"
+  },
+  {
+    "type": "boolean"
+  },
+  {
+    "type": "null"
+  }
+]

First observedv2.0.1Sep 23, 2026

TDQS

A3.6/5.0

Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is fully covered. The description's only added behavioral claim, 'read-only fallback', is consistent but redundant; it says nothing about what metadata is fetched, latency, or completeness of the inventory.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two tight sentences with the resource description front-loaded and the qualifier second. Nothing is padded or repeated from the title.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With an output schema present and a fully documented single parameter, the description covers what the tool returns at a high level. The only unresolved gap is the unexplained 'fallback' framing, which should identify the primary tool it backs up.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

There is a single parameter with 100% schema description coverage ('GA4 property ID (numeric, e.g., 123456789)'), so the schema carries the full burden. The description adds no meaning about propertyId beyond what the schema states, which is the expected baseline at this coverage level.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource: lists custom dimensions and custom metrics from GA4 Data API metadata. The scope is clear enough to distinguish it from report-running siblings, but it never names or contrasts the closest relative, ga4_get_metadata, leaving the boundary implicit.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The phrase 'Read-only fallback for custom definition inventory' implies a usage condition, but it doesn't say what it is a fallback to or when an agent should prefer it over ga4_get_metadata or ga4_get_property_configuration. The agent must infer the selection rule.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.