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

Annotations already declare readOnly, idempotent, non-destructive and open-world, so the safety profile is covered. The description adds meaningful context beyond them: no signing, no payment is sent, and the probe is confined to a single explicit resource.

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?

Two tight sentences with no filler; the safety constraint and action come first, then the usage condition. Every clause carries information.

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 values need not be described. The definition covers safety, scope, and when-to-use adequately, though it says nothing about error behavior when the resource is not payment-gated.

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 single parameter already documents 'Exact public HTTP(S) paid resource to probe.' The description reinforces the singular, explicit nature of the target but adds no syntax or format detail beyond the schema, so the baseline 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 (inspect/probe), an exact resource type (one explicit public machine resource), and the target evidence (x402 v2 HTTP 402). The safety qualifier 'without signing or sending payment' and the 'one explicit resource' scope clearly separate it from the sibling audit/diagnose/verify tools.

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 a clear trigger ('Use when an agent needs to diagnose payment-gating interoperability') and contrasts it against an alternative inference path ('rather than infer x402 from a storefront'). No explicit when-not conditions or named sibling routing, so it falls short of a 5.

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