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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety bar is lower. The description goes further with 'never signs or pays,' which adds substantive context beyond readOnlyHint — it clarifies no wallet interaction or payment side effect occurs. It stops short of noting rate limits or timeout/retry behavior.

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?

One dense, front-loaded sentence: the core action leads and the graded checklist follows, then the safety clause. Every listed item is informative rather than filler, though the enumeration is long enough to slightly tax readability.

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 carries the return-value burden, and it does so by enumerating the graded fields (status, headers, version, network, asset, payTo, domain, CORS, HEAD parity, discovery). That is nearly complete for a two-param diagnostic tool; only output shape/format is left unspecified.

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 description coverage is 100%, so the schema already documents both params including the method enum default. The description adds nothing about the parameters; 'HEAD parity' alludes to a check performed, not to parameter behavior. Baseline 3 is appropriate when structured fields carry the load.

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 — 'Fetch a paid URL without paying and grade its x402 402 challenge' — and enumerates exactly what is graded (status, PAYMENT-REQUIRED header, version, network, USDC asset, payTo, EIP-712 domain, CORS, HEAD parity, discovery metadata). There are no siblings to differentiate from, and an agent can tell precisely what this tool returns.

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: probe an x402 endpoint's challenge without paying. The description never states when to reach for this tool versus other validation approaches or any prerequisites (network reachability, target must be x402-enforcing). Adequate but leaves selection reasoning to inference.

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