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

Annotations already provide readOnlyHint, idempotentHint, and destructiveHint, establishing a safe, side-effect-free profile. The description adds useful context by stating it probes 'without signing or paying' and that it produces a 'deterministic health receipt,' which aligns with and enriches the annotation hints. No contradictions exist.

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 sentences, front-loaded with the main verb and target, and every clause adds relevant information. There is no redundancy or filler, making it highly concise and well-structured.

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?

Given the rich schema and annotations, the description is sufficient. It explains the tool's function, safe read-only nature, and the purpose of the key optional parameter. It does not detail error handling or output structure, but an output schema exists and the tool's purpose is clear, so this is not a critical 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 coverage is 100%, so the baseline is 3. The description adds meaning by explaining that the 'expected' parameter is used 'to verify payment metadata' and mapping its sub-fields (network/asset/price) to that purpose. This goes slightly beyond the schema, though mode and method still rely on their enum descriptions.

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 uses the specific verb 'Probe' and clearly identifies the target resource ('public x402 paid endpoint') and the key outcomes ('parse the HTTP 402 challenge' and 'receive a deterministic health receipt'). It distinguishes itself from sibling tools like scan_x402_resource by emphasizing the unpaid, no-signature probing approach.

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 states the primary use case: probing a paid endpoint without signing or paying, which clearly indicates when this tool is appropriate. However, it does not explicitly reference sibling tools or state when not to use it, so there is no direct exclusions or alternative guidance.

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