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

Annotations already indicate readOnly, idempotent, and non-destructive behavior, and the description adds meaningful behavioral detail: it sends a request with 'no payment header', never settles a payment, quotes the server's own words, and 'nothing moves.' This clearly discloses what happens and what does not happen, with no contradiction against the annotations.

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?

The description is compact and front-loaded with the primary action, then adds a useful distinction from the registry flag and a safety clarification about payments. Each sentence contributes meaningful guidance without redundancy or padding.

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 only two parameters and full schema coverage, the description is nearly complete. It explains the protocol behavior, the output concept ('report whether the server actually demands payment'), and the safety stance. It could be slightly more explicit about the exact response shape since there is no output schema, but the current wording is sufficient for correct invocation.

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 input schema fully documents `chainId` and `tokenId`. The description does not add parameter-level detail, but given full schema coverage, the baseline of 3 is appropriate.

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 states a clear specific action: 'Send the opening request of the x402 protocol — no payment header — and report whether the server actually demands payment.' It identifies the resource (the agent server), the operation (probe), and the outcome (boolean-style report). It also distinguishes itself from merely reading the self-reported registry flag.

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?

The description gives clear context for when to use this tool: when you need the empirical answer to whether an agent really charges, rather than trusting the registration's self-declared `x402_supported` flag. It does not explicitly name a sibling alternative or list when-not-to-use conditions, but the contrast with the registry flag is enough to guide selection.

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