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

Goes well beyond annotations: explains 'Never signs', that failed calls are free, the charging model, and explicitly justifies why readOnlyHint is false ('Reads or computes only; not marked read-only because each call is charged'). This is exactly the kind of annotation-adjacent context 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 the no-payment guarantee, and every clause carries information. It is dense to the point of being crowded (price, listing-quality score breakdown, payment options all in one paragraph), but no sentence is wasted.

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 compensates by enumerating the returned fields (USD price, network, asset, recipient, scheme, timeout, listing-quality score) and disclosing the payment model. Nothing needed to call it correctly is missing.

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% and the schema already documents the single 'url' parameter in detail, so the baseline is 3. The description adds a concrete example URL but no additional format or constraint semantics beyond what the schema states.

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') and immediately specifies the scope ('without paying (v1 body or v2 header)'). No sibling tool overlaps this function, so no differentiation is needed.

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?

Explicit when-to-use: 'Use before buying from an unfamiliar seller or to debug your own listing.' It does not name an alternative tool for those scenarios (e.g. check_counterparty), so it falls short of full alternative routing, but the context is clear.

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