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

With no annotations, the description carries the burden well: it discloses the return payload (answer plus lowercase SHA-256), the verification purpose of the hash, and the commercial model ($0.005 per call via x402/USDC), which is critical operational context. It omits error/failure behavior and does not flag that the plaintext answer is returned alongside the hash, which slightly undercuts the 'without reading the solution first' framing.

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?

Three sentences, front-loaded with the 'Use when' clause and with pricing last. Slight marketing phrasing ('The hash is the point') spends words on persuasion, but the content is dense and nothing is redundant with the 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 no-annotation, no-output-schema tool, the description covers what matters: what comes back, the cost model, and the verification use case. The one gap is the internal tension of returning the plaintext answer while advertising blind checking, plus no note on response shape beyond the two values.

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 all four parameters are already documented, including seed determinism and exclude. The description only echoes the difficulty and language filters and adds nothing about seed or exclude beyond the schema, so the 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: returns one riddle filtered by difficulty, in English or Spanish, together with the answer and its lowercase SHA-256 hash. It also explicitly differentiates from siblings ('no other riddle endpoint lets you do this'), so an agent can pick it out of the content_* family 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?

'Use when an agent has to run a guessing game and must mark the answer without seeing it first' gives a clear triggering condition. It contrasts with unnamed alternatives rather than naming a sibling to use instead, so there is no explicit when-not guidance, but the selection context is unambiguous.

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