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

With annotations present (readOnlyHint=false, openWorldHint=true, idempotentHint=false), the description still adds real context: 'Never signs', the v1 body vs v2 header decoding paths, and the $0.002 USDC-on-Base per-successful-call cost, which explains why readOnlyHint is false. It does not cover failure/error behavior, but the fee and no-sign guarantee are exactly the behaviors an agent needs.

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 action and no-sign guarantee, then the return fields, then usage and cost. It is dense and somewhat run-on in the return-value enumeration, but every clause carries information and nothing is filler.

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?

There is no output schema, yet the description specifies the returned fields (USD price, network, asset, recipient, scheme, timeout, listing-quality score and its inputs), plus cost and usage. For a single-parameter tool this is complete enough for an agent to call it correctly and anticipate the response.

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?

Only one parameter and schema coverage is 100%, so the schema fully documents 'url' (with the https/query guidance). The description's 'for https resource URL' slightly reinforces it but adds no syntax or format detail beyond the schema. Baseline 3 is 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?

States a specific verb and resource: 'Decode any public x402 endpoint's 402 payment requirements without paying.' It enumerates exactly what it returns (price, network, asset, recipient, scheme, timeout, listing-quality score), leaving no ambiguity about scope. No sibling tool covers x402 payment inspection, so it is trivially distinguished.

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?

Gives explicit trigger conditions: 'Use before buying from an unfamiliar seller or to debug your own listing.' This covers the two main scenarios clearly. It stops short of naming exclusions or any alternative tool, but no sibling overlaps this niche.

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