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

Annotations already declare readOnlyHint, idempotentHint, and a closed-world hint, so the safety profile is clear. The description adds useful scope information beyond that: what fields are returned (meaning, register, figurative status) and approximate lexicon sizes per language, making the limited coverage of the resource explicit.

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 compact sentences front-load the purpose and modes, with the parenthetical coverage counts giving useful scoping detail without waste. Every clause 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?

With an output schema present, the description does not need to explain return values, and annotations cover safety. It communicates the resource scope and the two main use modes, though it could be slightly more explicit about how concept and expression interact and what happens when neither is supplied.

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 75%, and the schema already documents lang, concept, and expression. The description's 'find one for an idea, or explain one' usefully suggests the concept vs. expression modes, but it does not clarify mutual exclusivity, the limit parameter, or the behavior of 'auto' beyond what the schema states.

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 states a specific resource (fixed expressions and idioms) and two clear modes: finding an expression for an idea, or explaining a given expression. It does not explicitly name or differentiate itself from the sibling lookup_word, so sibling routing is only implicit rather than explicit.

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 phrase 'find one for an idea, or explain one' implies the two usage modes and loosely maps them to the concept vs. expression parameters. However, it gives no explicit exclusions, prerequisites, or guidance about when to use lookup_word instead, leaving alternative selection to inference.

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