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

Goes well beyond the readOnlyHint/openWorldHint annotations: it discloses cost ($0.01 USDC per call over x402), that failed calls are free, the quote-then-sign flow, the ranking methodology and its anti-gaming rationale, and an honest conflict-of-interest disclosure about Tollkit ranking its own tools (marked sold_by_tollkit). This is exactly the extra context annotations cannot carry.

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?

Two tight paragraphs, purpose front-loaded in the first sentence, with pricing and the quote mechanism at the end. The Tollkit disclosure is a slight digression but is materially relevant to trusting the ranking, so it earns its place.

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 discovery tool with no output schema, the description covers what is returned (ranked sellers, one endpoint each, price, caution flags), the cost model, and the two-step payment flow. It is nearly complete; only the unmentioned `limit` and the exact response shape are left unaddressed.

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 67%: `task` and `payment` are documented in the schema, while `limit` has none. The description usefully reinforces the payment flow (omit it to receive a quote; sign and call again) but says nothing about the undocumented `limit` parameter, so it only partially compensates for the coverage gap.

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 and resource ('Find the best paid x402 API for a task') and details what the result contains (ranking by paying wallets/repeat buyers, one endpoint per seller, price, caution). However, it never names the sibling it should be distinguished from (e.g. x402_seller_lookup or find_service), leaving the agent to infer the boundary.

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 quote-first workflow ('Call without `payment` to get a quote') and 'Failed calls cost nothing' are actionable invocation guidance, but the description gives no when-to-use/when-not guidance relative to the many service-discovery siblings. Usage is implied by the task parameter rather than routed explicitly.

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