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

Annotations cover the read-only/open-world safety profile, but the description adds genuinely non-derivable behavior: the x402 payment model, the exact cost ($0.002 in USDC), accepted chains, and that failed calls are free. It omits pagination/rate-limit behavior, but the output schema covers return shape.

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 compact sentences front-load the capability and the key negative constraint, followed by the payment terms. Every clause (fields, filter, no prices, price/failure policy) carries information an agent needs.

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 annotations, an output schema, and full param coverage handled elsewhere, the description fills the main remaining gap by disclosing the paid-call model. Minor omission of rate limits or result-ordering behavior keeps it from a 5.

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% and both parameters (limit, search) are fully documented there, so the baseline is 3. The description only restates the filter concept ('name or code fragment') without adding format, range, or matching semantics beyond the schema.

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 ('Currency list from Coinbase's public v2 API') with the exact fields returned (code, name, minimum size) and the filter capability. The clause 'Reference data only; no prices' explicitly distinguishes it from the numerous price/ticker siblings like finance_coinbase_exchange_products and crypto_coinbase_spot_exchange.

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?

'Reference data only; no prices' plus the name/code fragment filter implies when to reach for it (enumerating or resolving currencies) versus price tools, which is real usage guidance. It stops short of naming an explicit alternative tool for price data, so it doesn't reach a 5.

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