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

Annotations only cover the safety profile (readOnlyHint/destructiveHint). The description adds substantial behavior the annotations cannot: inclusive dates in property timezone, the five data_availability states with the critical clarification that no_rows and access_error do not mean zero, a retry rule, and a prompt-injection warning for externally-authored strings. This is exactly the value-add expected beyond structured annotations.

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?

Front-loaded with purpose then behavior; every sentence carries weight. The data_availability enumeration is long but each state is genuinely load-bearing, and the injection warning is compact and placed last where it belongs.

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?

With no output schema, the description takes on the burden of explaining return semantics and does so thoroughly: timezone is returned with the result, and the data_availability states disambiguate the most likely agent misinterpretation (reading empty/error as zero). Nothing essential for a correct call is missing.

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 100%, and the descriptions are already rich (metric name-to-response mapping, date formats, property_id formats, account_link_id auto-resolution). The prose adds no additional parameter semantics beyond that, so the baseline 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?

States a specific verb+resource+scope: 'Run a GA4 report for one property over a date range.' An agent immediately knows this fetches GA4 reporting data. It does not explicitly distinguish itself from siblings like google__search_console__performance or google__analytics__measurement__audit, so it falls short of a clean 5.

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?

Gives explicit recovery guidance ('On no_rows, widen the date range and call again') and notes read-only status, which is useful conditional context. However it never states when to choose this tool over the sibling reporting tools (e.g. search_console__performance, measurement__audit), leaving selection to inference.

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