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

Annotations already declare readOnlyHint=true, openWorldHint=true, and destructiveHint=false, so the safety profile is covered by structured data. The description adds two useful behavioral facts: fields are validated against the property metadata catalog, and GA4 API field names (not display names) are required. It omits row limits, failure modes on invalid field combinations, and latency/cost expectations for a flexible query tool.

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 sentences, no filler, with the core action stated first and the field-naming constraint second. Every clause carries information. It is on the terse side for a ten-parameter tool, but that thinness is a completeness issue rather than verbosity.

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?

This is the most flexible GA4 tool in a large family, with 10 parameters and no output schema, yet the description supplies no routing guidance relative to the prebuilt GA4 reports and no explanation of how the date parameters combine. An agent can invoke it, but it cannot confidently decide between this and ga4_overview or ga4_pages for a given user question.

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 description coverage is 70%, so most parameters (detail, property, date_range, start_date, end_date, folder, language) are already documented in the schema. The description adds the naming-convention constraint for dimensions and metrics and the validation source, which is real value, but it says nothing about the date_range versus start_date/end_date interaction or the limit behavior. Baseline 3 is appropriate given the schema does most of the work.

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?

States a specific verb and resource: run a GA4 report parameterized by dimensions and metrics. The added detail that fields are validated against the property's getMetadata catalog makes the purpose concrete. It stops short of distinguishing itself from the many fixed-purpose GA4 siblings (ga4_overview, ga4_pages, ga4_traffic_acquisition), leaving the 'custom' distinction implicit in the name.

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?

No when-to-use guidance is given despite roughly a dozen GA4 siblings that return prebuilt report shapes. An agent must infer that this is the escape hatch for arbitrary dimension/metric combinations rather than for standard overview or page questions. No mention of when a validation failure should steer the agent to ga4_custom_definitions or another tool.

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