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

Annotations only declare readOnlyHint and openWorldHint; the description goes well beyond them by disclosing the ranking signal (calls per paying wallet over 30 days), that top candidates are probed live for payment status and price, the per-result fields and flags, and that it never pays. This is unusually rich operational context.

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?

Front-loaded with the core promise, then methodology, then output shape. Dense but nearly every clause carries information. It runs long as a single paragraph, and a couple of list-like enumerations would read more cleanly.

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?

Despite having no output schema, the description enumerates the returned fields (URL, method, price, network, rationale, flags) and the flag semantics, plus the live-check and ranking behavior. An agent has everything needed to call it and interpret results.

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 schema already documents all four parameters. The description adds meaning beyond the schema by clarifying what check_live actually verifies (still asking for payment, at the listed price) and by tying limit to the 'top 1-5' framing and price comparisons to max_price_usd.

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: retrieve the top 1-5 pay-per-call x402 APIs matching a described task, drawn from an hourly index of ~38,000 endpoints. The scope is precise and unambiguous. It does not, however, distinguish itself from siblings like check_before_paying or x402_market_report, which an agent may find overlapping.

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?

Usage is implied by the phrasing (describe a need, get ranked APIs), and the ranking rationale gives implicit context for when results are trustworthy. But there is no explicit when-to-use vs when-not guidance and no named alternative tool for adjacent tasks such as vetting a single endpoint.

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