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

Annotations already declare readOnly, idempotent, closed-world and non-destructive, so the safety profile is covered. Beyond that the description adds genuine value by disclosing the aggregation axes and that a computed 'mastery stage' is returned per bucket — a non-obvious derived field. No auth, caching, or scope caveats are mentioned, which keeps it short of a 5.

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, zero filler. The output shape is front-loaded first and the invocation trigger second, which matches how an agent reads a definition.

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 an output schema present and annotations covering safety, the description need not explain return structure, and it is adequate for correct invocation. The one remaining hole is the unresolved boundary with the sibling poetry-stats tool, which could still cause a wrong tool pick.

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 no parameters, so there is no per-parameter meaning to convey; baseline 4 applies. The description correctly implies a single implicit scope (the current reader) without adding confusing pseudo-parameters.

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 ('shows how widely the reader has read poetry... by poetic form, by era and by poet') and enumerates the returned metrics (distinct poems read, total reads, mastery stage). An agent knows exactly what data this produces. It does not, however, differentiate itself from the close sibling get_poetry_reading_stats, which likely overlaps in subject matter.

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 second sentence gives an explicit trigger: when the reader asks which forms of poetry they have read, or how their poetry reading spreads across eras and poets. That is clear positive guidance, but no exclusion is given against the near-neighbour get_poetry_reading_stats or the broader get_reading_domain, leaving an overlap the agent must guess through.

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