Slow rendering rate

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

Annotations already declare readOnly/idempotent/openWorld/non-destructive, so safety is covered. The description adds genuinely useful behavioral context beyond that: the shape of the output (daily values), the inclusion of 7- and 28-day user-weighted aggregates, and the unit convention (fractions, 0.01 = 1%), which prevents a real misinterpretation of returned data.

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 compact sentences, front-loaded with the metric and source, with the second delivering the unit caveat. Nothing is wasted and no filler is present.

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 does part of the return-value work by stating the daily granularity, the 7/28-day aggregates, and the fractional unit. Missing only deeper return details (pagination, dimension output shape), which keeps it at 4 rather than 5.

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%, with days, filter, dimensions, and package_name each documented in the schema. The description adds no parameter-level detail (e.g. dimension syntax or filter semantics), so it sits at the baseline of 3.

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 metric ('Daily slow rendering rate from Android vitals') with named API source, which inherently separates it from metric siblings like crash_rate and anr_rate. However, it never explicitly names those siblings or explains how this differs from vitals_summary/vitals_by_version.

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 no when-to-use guidance or mention of alternatives. The agent must infer that this is the tool for slow-rendering specifically, and cannot tell from the description when to prefer vitals_summary or vitals_by_version instead.

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