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

No annotations are provided, so the description carries full burden. It thoroughly explains the tool's behavior: performs a GET without X-PAYMENT header, checks the 402 challenge against 16 rules, and returns specific status categories (healthy, advisories, defects_found, not_x402, unreachable). It also clarifies that each finding cites its source (spec or facilitator rejection). This is comprehensive and goes beyond the minimal.

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 fairly concise for the amount of information it conveys. It front-loads the core action and then details the handshake process, rule checking, and status reporting. It could be slightly shorter by removing some redundancy (e.g., 'what it observes about it' is unnecessary), but it is well-structured and efficient given the complexity.

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?

The description is complete for a tool with one parameter, no output schema, and no nested objects. It explains the input constraints, the probing logic (including the handshake and rule checks), and the possible return statuses. No missing information is apparent given the tool's complexity. The lack of an output schema is compensated by the detailed description of the output categories.

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?

There is only one parameter (url) with 100% schema description coverage. The description adds context by noting that private and loopback addresses are refused, which is not in the schema description. This adds practical usage guidance beyond the schema. The high schema coverage means the baseline is 3, and the extra context justifies a 4.

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 clearly states what the tool does: it probes an x402 seller endpoint and reports observations. It distinguishes itself from sibling tools like 'explain_defect' and 'list_checks' by focusing on endpoint probing rather than defect explanation or check listing. The verb 'probe' and resource 'x402 seller endpoint' are specific and unambiguous.

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 implies when to use this tool: to test an x402 endpoint and get a health status. It does not explicitly state when not to use it or mention alternatives, but the context of sibling tools ('explain_defect', 'list_checks') provides some differentiation. The lack of exclusions is a minor gap, but the use case is sufficiently clear.

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