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

Goes well beyond the annotations: it discloses that validation mirrors the free check the API runs before payment, that a refused or empty query surfaces here, that the paid endpoint is never called and nothing is paid. It also explains the payment model (x402, no account or API key, USDC on Base), which no annotation conveys.

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 is returned, then usage, then safety, then payment mechanics. Every sentence carries information an agent needs, with no restatement of the name or title.

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 does the work of describing the return payload (URL, price, network, asset) and the observable failure mode (refused or empty query). The one gap is that it doesn't say whether the response is cached or how stable the quoted price is, which matters for a pre-payment check.

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 baseline is 3, but the description adds meaning: the params you supply are run through the same validation gate as the real call, so they are not just passthrough. It doesn't restate formats, but that is already handled by the schema.

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?

Names a specific verb and resource: it returns the exact URL to call for a paid answer, plus price, network and asset. An agent can tell this apart from a live data fetch because the description states it never calls the paid endpoint. It stops short of naming siblings like list_endpoints or get_sample directly in the prose.

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?

Says to pass the endpoint key and the query parameters you plan to send, and explains the result is the same free pre-payment check the API runs, which tells the agent when this is the right call. It doesn't explicitly say to run list_endpoints first or when to skip this step, so the routing guidance is implied rather than stated.

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