ga4_custom_metrics

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

With no annotations, the description carries the full burden. It does disclose real prerequisites (Admin API enabled on the quota project, Viewer role on the GA4 property) and that access failures come back with remediation text, which is genuine behavioral value. It falls short on whether the operation is read-only, whether it returns all metrics or a filtered set, and there is no output schema to compensate.

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?

It is short and front-loads the resource definition, and the prerequisite/error-handling clause is useful rather than filler. But it mixes Spanish ('Lector (Viewer) en la propiedad de GA4') into an otherwise English description, and the sentence structure is dense enough that the missing action verb gets lost.

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 one-parameter, zero-required tool with full schema coverage, the prerequisite block is enough to attempt a call and recover from auth errors. The critical gap is that the tool's actual action is never stated, and with no output schema there is nothing else to tell an agent what comes back.

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?

Schema coverage is 100% for the single 'property' parameter, including the default-property fallback, so the schema does the semantic work. The description adds nothing about the parameter — no cross-reference to ga4_list_properties or ga4_set_default for choosing a property — matching the baseline of 3 when the schema is self-sufficient.

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 defines the resource ('Numeric event parameters registered as custom metrics') and how they are referenced in reports ('customEvent:<parameter>'), which is useful domain context. However, it never states the action the tool performs — listing, retrieving, or registering — so an agent must infer that this returns the property's custom metrics list. Sibling ga4_custom_dimensions is never mentioned as the parallel resource.

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?

There is partial routing guidance: it points to ga4_check_access when access problems occur, which is useful triage. But it gives no explicit when-to-use versus ga4_custom_dimensions or ga4_run_report (where custom metrics are consumed), and no statement of when-not to call it.

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