ga_list_custom_metrics

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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds some context about the configured property and the API-name output, but it does not disclose pagination, limits, or other behavioral quirks; this is acceptable but not exceptional.

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

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

Two short sentences with no filler. The action and scope are front-loaded, and the use-case sentence earns its place by explaining why an agent would call the tool.

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

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

For a simple read-only list tool with one optional, well-documented parameter, the description is nearly complete. Without an output schema, it helpfully states that the result surfaces custom metric API names for reports, though a bit more detail about the response shape would make it fully complete.

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

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

The input schema documents propertyId fully, including accepted formats and how to discover IDs, with 100% schema description coverage. The description adds no parameter-specific detail, so the schema bears the load and the baseline of 3 applies.

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

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

The description opens with 'List all custom metrics defined for the configured GA4 property', a specific verb and resource that clearly distinguishes it from sibling tools such as ga_list_custom_dimensions and ga_list_key_events. It immediately tells the agent what object is acted on.

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

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

The second sentence, 'Use this to discover custom metric API names for reports', provides a clear intended use case. It does not explicitly mention when not to use it or name alternatives, but the context is concrete enough to route an agent correctly.

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