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

The description goes well beyond the annotations by disclosing that no bearer/x402 auth is needed, k is forced to 1, quota is 1 request per IP per UTC day, the success response shape, and the error object on exhausted quota. These are meaningful behavioral details not available from annotations alone.

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 compact and front-loaded with the core purposeholiday. Every sentence contributes operational detail; there is no filler, repetition, or unnecessary background.

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?

Given the schema covers parameters and annotations indicate read-only open-world behavior, the description supplies the remaining operational context: endpoint mapping, authentication, quota, forced k, and response shapes for both success and quota exhaustion. An agent has enough to invoke it correctly and interpret the outcome.

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 the schema documents query and cutoff fully. The description adds no extra parameter-level meaning beyond what the schema already states, making the baseline 3 appropriate.

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 clearly states this is a free-taste probing tool for the Fillin corpus and identifies it as the MCP twin of POST /v1/probe. It conveys the action and resource, though it does not explicitly contrast itself with the more capable sibling fillin_query or fillin_answer.

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?

It states the quota and auth-free context, so an agent knows when it is usable, but it offers no guidance on when to prefer this tool over siblings like fillin_query or fillin_market_search. It does not explain which scenarios call for the full-featured alternatives.

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