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

The description says the tool pays real money from the provider's wallet and 'costs 1 USDC per call', which is a spend with external side effects, while annotations declare readOnlyHint=true and idempotentHint=true. Repeat calls are materially non-idempotent because each one costs another 1 USDC. This is a direct annotation contradiction.

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?

Four dense sentences, front-loaded with the trigger condition, then outputs, then edge cases, then price. It loses a point because the pricing statement is internally inconsistent: 'up to $0.05' capped spend versus 'costs 1 USDC per call' cannot both be the price the agent pays.

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 needn't be explained, and the description still usefully names the three verdicts and the receipt. However, the conflicting cost figures ($0.05 cap vs 1 USDC per call) leave an agent unable to judge the actual spend of calling it, which is the single most important fact for a paid probe.

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 url and method are already fully documented including the URL-encoding/public-host constraints and the empty-POST-body behavior. The description adds no parameter-level detail beyond schema (its 'up to $0.05' cap is a cost note, not a parameter note), so 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+resource+outcome: pays an x402 endpoint once and returns PASS, FAIL or INCONCLUSIVE with the receipt. The framing ('proof that an x402 endpoint takes a real payment') cleanly separates it from the sibling get_x402_lint, which is a static check.

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?

'Use when an agent needs proof that an x402 endpoint takes a real payment' gives a concrete trigger condition, and the note that a 503 or 404 is not charged tells the agent how to interpret edge results. It never explicitly says when to prefer get_x402_lint instead, so the routing to the sibling is left implicit.

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