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

The description adds meaningful behavior beyond the readOnlyHint/idempotentHint annotations, including the grouped-by-sense return structure, part-of-speech and definition inclusion, and the fallback to spelling suggestions for unknown words. This gives the agent a solid mental model of both success and miss behavior.

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?

The description is tight and front-loaded: it names the resource and action immediately, then provides return details and an example. Every sentence contributes useful information, and the example is placed at the end to avoid interrupting the core guidance.

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, the description appropriately explains the return payload and edge-case behavior. The optional _apiKey parameter is documented in the schema, and the input word is exemplified in both schema and description. No critical information needed to invoke the tool 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%, so the schema already documents both parameters thoroughly. The description provides a usage example but does not add meaningful semantic detail beyond the schema's existing parameter descriptions, keeping this at the baseline 3.

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 specifies a concrete action ('Look up a word') and a specific resource ('Merriam-Webster thesaurus'), which cleanly distinguishes it from sibling tools like define. It also details the expected content—synonyms, antonyms, part of speech, and definitions—so an agent knows exactly what this tool provides.

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 description gives clear usage context: look up a word to get thesaurus-style information. It does not explicitly contrast with define or other sibling tools or state when not to use it, but the distinct purpose and output details imply the correct use case. No misleading guidance is present.

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