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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds behavior the annotations cannot: exact return contents, the truncation rule ('a poem of 1 to 3 lines whole'), and conditional fields ('a short summary when the library has one', analysis link 'when there is one').

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 front-loaded sentence that leads with the purpose and then the payload; no filler. It is dense with field lists but every clause carries information an agent needs given there is no output schema.

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 one-parameter, read-only, non-paginated lookup with no output schema, the description supplies the id source, the full return surface, truncation behavior, and conditional-field caveats. Nothing essential to making the call correctly 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 coverage is 100% and the only parameter is fully documented there, so the baseline is 3. The description adds provenance for the id (find_poems or a poem page URL), which the schema pattern alone does not convey.

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?

Names the specific resource and its selector ('One poem by its id') and immediately enumerates what comes back: title, poet, language, line/stanza counts, opening, summary, links. An agent can distinguish it from siblings like find_poems (which supplies the id) without opening the schema.

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?

Explicitly states where the id comes from ('from find_poems or a poem page URL'), which is real usage guidance for the one input that matters. It stops short of saying when to prefer this over poem_of_the_day or get_analysis, so it is clear context rather than full routing.

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