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

Annotations already declare readOnlyHint and idempotentHint, and the description does not contradict them. It adds valuable behavioral context: the data is trailing 30-day, historical, and explicitly not a guarantee of future performance—useful caveats beyond the 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?

Two sentences with no filler. The first sentence states exactly what is returned and how it is grouped; the second captures the caveat. Every word earns its place.

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 zero-parameter read-only stats endpoint, the description covers the return content, time window, grouping, and a usage caveat. Combined with readOnly/idempotent annotations and no output-schema requirement, nothing essential is missing for an agent to call it and interpret results.

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?

The tool takes zero parameters and schema description coverage is 100%, so there are no parameter semantics to clarify. The description focuses on the output dimensions (counts, timing, platform, currency) rather than inputs, which is appropriate for a no-parameter tool.

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 uses a specific verb ('Return') and specifies the resource ('trailing 30-day fill counts and first-fill timing'), the grouping dimensions ('by payout platform and currency'), and the time window. This clearly distinguishes it from other peer_cash_* tools like peer_cash_estimate or peer_cash_quote_source.

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?

It states the intended use case ('historical routing evidence') and adds a strong exclusion ('never as a guarantee'), which tells the agent this is diagnostic, not predictive. However, it does not explicitly name alternative tools such as peer_cash_estimate for forward-looking needs, so it falls just short of full routing guidance.

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