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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false, so safety is covered. The description adds real behavioral context beyond that: an unknown phrase does not error but returns the closest matching phrases, which is exactly the kind of degradation behavior an agent needs to know.

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, no filler, with the primary capability front-loaded and the fallback case appended where it belongs. Every clause carries information.

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 present, the description still enumerates the three return components (meaning, origin, titles used in) and the near-miss fallback. Minor gap: it doesn't indicate result count or ordering for the 'closest phrases' case.

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%, with the phrase example and the full language enum plus its defaulting rule already documented in the schema. The description adds no additional param meaning, so baseline 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?

Specific verb+resource ('Explain a saying or idiom') followed by the exact content returned: meaning, origin, and library titles that use it. That distinguishes it from book-oriented siblings like get_book or search_books, though no sibling is named explicitly.

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?

Usage is implied by the resource type (idioms/sayings rather than books or passages), but the description never states when to prefer this over find_quote_source or search_books, nor any prerequisites. The nearest-alternative routing is left to inference.

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