Slow start rate

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and openWorldHint=true, so the safety profile is covered. The description adds genuine behavioral context by disclosing the return shape ('7- and 28-day user-weighted values') and the value encoding ('0.01 = 1%'), which is not available in any structured field. It stops short of describing pagination or how the 7-/28-day values are keyed.

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?

A single tight sentence that front-loads the metric identity and data source before the return-value and unit details. Every clause earns its place, with only minor compression possible.

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 carries the burden of explaining return values, and it does so adequately by naming the 7- and 28-day user-weighted values and the fraction encoding. For a read-only metric tool with fully documented parameters, this is nearly complete, missing only response structuring details.

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%, so all four parameters (days, filter, dimensions, package_name) are already documented in the schema, including defaults and examples. The description adds no parameter-level syntax or constraint details beyond the schema, so 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?

States a specific verb and resource ('Daily slow start rate from Android vitals'), names the data source (Play Developer Reporting API), and clarifies the metric's composition (7- and 28-day user-weighted values) plus its unit ('fractions (0.01 = 1%)'). This clearly distinguishes it from sibling metrics like crash_rate, anr_rate, and slow_rendering_rate.

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 description explains what the tool returns but never says when to call it versus sibling vitals tools (crash_rate, anr_rate, vitals_summary), nor any prerequisites or exclusions. Usage is only implied by the metric name, leaving the agent to infer selection from the name alone.

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