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

Annotations already establish this is a read-only, non-open-world call, so the safety profile is covered. The description adds genuinely new behavioral context: the $0.002 USDC cost, the prepaid-key vs x402-per-call payment paths, and the no-charge-on-error policy. It does not cover rate limits or latency.

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, cost front-loaded, then the use case, then the error/pricing caveat. Every clause 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 enumerating the returned metrics in place of one, and it covers cost, payment paths, and error semantics. An agent has enough to call it correctly; only minor operational details such as response shape/formatting are unstated.

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 both parameters (q, api_key) are already fully documented in the schema, including accepted symbol/id/name forms and the x402 payment mechanism. The description adds no parameter-level detail beyond that, which matches the baseline 3 when the schema does the heavy lifting.

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 (lookup) and resource (one coin) and enumerates exactly what comes back: live price, market cap, volume, 1h/24h/7d change, distance from ATH. It does not explicitly distinguish itself from similarly named siblings like lookup_token_risk or lookup_polymarket, but the returned-field list makes the purpose unambiguous.

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 you need one coin's live price..." gives a clear triggering condition, and "Unknown coin = error, no charge" sets an expectation for failure behavior. No explicit when-not-to-use or named alternative is given, 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.