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

With readOnlyHint and openWorldHint already in annotations, the description adds useful behavioral context: the tool itself costs $0.01 USDC via x402, it probes external endpoints without paying them, and it returns pass/warn/fail checks plus fix hints. No annotation contradiction is present.

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 dense but focused; the initial paid cost is front-loaded and the colon list efficiently enumerates what is checked. The final sentence about the return shape and REST equivalent adds value without repetition.

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 no output schema, the description explicitly states the return format (checks with pass/warn/fail and fix hints) and lists the input-output scope. It is sufficient for an agent to invoke and interpret results, though exact response field names are not specified.

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 schema fully documents url and method. The description does not add extra meaning beyond mentioning the paid/network context, but the baseline of 3 is appropriate because the schema carries the parameter semantics.

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 the specific action (diagnose), target (x402 endpoint), and the detailed check areas, so an agent knows exactly what the tool covers. It stops short of explicitly contrasting itself with the sibling tools (x402_preflight, x402_quick_check), so it is clear but not fully sibling-differentiating.

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 the main use case: inspect an x402 endpoint the way a paying agent would without incurring payment to the endpoint. It does not, however, tell the agent when to choose this over x402_quick_check or x402_preflight, nor give any exclusion criteria.

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