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

Annotations give readOnlyHint/openWorldHint, and the description adds genuinely non-obvious behavior: the full validation checklist, the tri-state outcome with a 0-100 score and per-failure fix, and the monetary cost ($0.01 USDC on Base via x402). Cost disclosure is high-value context the annotations do not carry, though failure modes like unreachable URLs or timeouts are not described.

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?

A single tight paragraph that front-loads the purpose, then the validation scope, then the return shape, then the price. Every sentence carries information an agent needs and nothing is padded.

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?

With no output schema, the description compensates by describing the pass/warn/fail result, score, and fix output, plus the invocation cost. It slightly undersells how the optional expect object changes failure determination, but overall it is complete enough to call correctly.

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 already documents url, body, expect, method and headers. The validation list loosely maps to the expect fields (network, asset, price) but adds no syntax or semantic detail beyond what the schema provides; 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 and resource ('audit x402 payability of a paying agent's API') and enumerates exactly what it validates (CAIP-2 network, USDC asset, payTo checksum, amount, EIP-712 domain, resource URL, Bazaar discovery). No sibling tool covers this ground, so differentiation is implicit and strong.

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?

Usage context is clearly implied ('Probes any x402 URL' to check whether a paying agent can actually pay it), but there is no explicit when-not guidance or named alternative among the many base_*/audit_* siblings. The price note hints at a decision factor but does not route the agent.

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