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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, yet the description still adds real behavioral context: a 10-second unsigned probe, no payment headers, and null-rather-than-invented-defaults for non-402 or incomplete challenges. It stops short of stating rate limits or permission requirements, so it is strong but not exhaustive.

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 purpose, then alias relationship, then allowed/forbidden usage, then result semantics — a logical ordering with no filler sentences. The phrase '10-second unsigned probe and result' is slightly compressed, but nothing 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?

An output schema exists, so return-value detail is not required, yet the description still covers the key edge case (null for non-402/incomplete challenges). Combined with a fully documented single parameter and safety annotations, an agent has everything needed to call it correctly.

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% for the single 'url' parameter, which already documents HTTPS-only, unsigned GET, and rejection of redirects/credentials/private targets. The description adds no parameter syntax or format detail beyond that, so the baseline of 3 applies.

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 ('Inspect a fresh x402 v2 challenge') plus the critical scope constraint that no payment is sent. It also identifies itself as a compatible alias of the sibling check_payment, so an agent can differentiate it without opening either schema.

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 positive guidance ('Use before a paid resource call') and explicit exclusions ('do not use as a signer, receipt verifier or settlement proof'), plus the alias relationship to check_payment. Both the when and the when-not are stated.

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