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

Annotations declare it read-only, idempotent and non-destructive, but the description goes well beyond: it never pays, sends exactly one unpaid request, and spells out the billing boundary (any HTTP answer including 4xx/5xx is billed; bad input, blocked hosts, connection failures and timeouts are not). It also discloses the transactional cost model — $0.01 per call, USDC on Base, MCP payments Base-only — which the agent cannot infer from annotations.

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?

Well front-loaded: purpose, then when-to-use, then mechanics, return shape, billing rules and price. Every sentence earns its place, though the dense parentheticals make some clauses heavy going.

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 carries the return-value burden and does so fully, enumerating httpStatus, isX402, x402Version, decoded accepts, discovery metadata presence and pass/warn/fail checks. Combined with the billing and cost disclosures and annotations covering safety, an agent has everything needed to call it 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 baseline is 3. The description restates the parameters ('GET with required url (optional method GET/POST, JSON body for POST)') but adds no syntax or format detail beyond the schema, which actually carries more nuance (POST retry on 405, 8KB body limit).

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 ('x402 endpoint checker') and immediately narrows the scope: sends one unpaid probe request and never pays. That distinctively separates it from generic siblings like http, fetch, or bazaar_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 before paying an unknown x402 endpoint, or to debug your own' gives two concrete triggering scenarios. There is no explicit when-not or named alternative (e.g., versus bazaar_check or http), so it falls short of a 5.

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