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

With no annotations, the description carries the full burden and does well: it discloses the deterministic UTC-date selection, reproducibility of past days, and a concrete cost/payment model ($0.005 per call over x402/USDC). This is real behavioral context an agent needs to call it. Only rate limits and failure behavior are unstated.

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?

Four sentences, front-loaded with what you get and the key differentiator (determinism), with pricing last. Each sentence earns its place, though the 'usual endpoints' jab is marginally marketing-flavored rather than operational.

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?

No output schema exists, yet the description names the return fields (definition, part of speech, example sentence), and covers determinism, language options, and cost. For a zero-required-param lookup tool this is essentially complete, missing only edge behavior (e.g., invalid dates, response format).

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 description coverage is 100%, so both 'date' (YYYY-MM-DD, UTC, defaults to today) and 'language' (en|es, defaults to en) are already fully documented. The description reinforces reproducibility and the language options but adds no syntax or format detail beyond the schema. 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?

States a specific verb+resource ('the word of the day') plus the exact return payload (definition, part of speech, example sentence), and differentiates itself from generic random-word endpoints. An agent can distinguish it from siblings like content_joke or content_fact 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?

Explains the determinism/reproducibility use case ('you can reproduce any past day by passing it') and contrasts against endpoints that return a random word, which is clear context for when this is the right tool. It stops short of naming a sibling alternative, but no sibling here serves the same purpose, so guidance is effectively complete.

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