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

Annotations already declare readOnly, idempotent, non-destructive and open-world behavior, so the safety profile is covered. The description adds value beyond them by disclosing that the call is free, that it is a DNS-pinned public HTTPS request, and that no payment is dispatched — meaningful operational context. It omits rate limits and response shape, hence not a 5.

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?

A single sentence, front-loaded with the key 'Free' qualifier and packed with non-redundant facts (probe type, inspected fields, no payment). Every clause earns its place with no 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?

For a read-only probe with safety annotations already present and no output schema, the description covers the essentials: what it targets, what data it surfaces, and the cost/no-payment guarantee. Only the method parameter and request failure behavior are unaddressed, a minor gap.

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 0%: neither the 'url' string (with its 10-1024 length bounds) nor the 'method' GET/POST enum is documented, and the schema is a nested request object. The description only implies the target URL via 'an x402 endpoint' and says nothing about the method parameter, so it fails to compensate for the coverage gap.

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?

The description names a concrete action (DNS-pinned HTTPS probe) and resource (an x402 endpoint) and states exactly what it inspects: the 402 quote, price, network and recipient. The 'no payment sent' clause implicitly sets it apart from the many prepare_*/create_* payment siblings, but it doesn't name a specific alternative, keeping it just below the top mark.

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?

'Free' and 'no payment sent' strongly imply this is a non-committal diagnostic you run before paying, which is real usage context. However, it never states when to prefer this over siblings like payment_capabilities or tx_preflight, nor any exclusions, so the guidance remains implied rather than explicit.

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