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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so the safety profile is covered. The description adds real value beyond that by disclosing the lookup output set, including the non-obvious onchain Base L2 settlement mapping (USDC/EURC), which an agent could not predict from annotations alone. It does not say what happens for an unrecognized code, keeping it below a 5.

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, no filler, with the validation scope front-loaded before the return-value list. Every clause carries information.

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?

For a single-parameter read-only lookup with an output schema, the description is sufficient; return values are additionally summarized. The only gap is error/not-found behavior for unknown codes, which would be useful in a validator.

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?

Only one parameter, and schema_description_coverage is 100%, so the schema already documents the accepted formats with examples. The description restates the alpha/numeric duality without adding syntax or edge-case detail, so the 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?

The description states a specific verb (validate) and resource (ISO 4217 currency codes), covering both alpha and numeric forms, and lists the returned fields. Among the sibling check tools (iban_check, swift_bic_check, ean13_check), the currency-domain scope makes it unambiguous which one to call.

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 is implied by 'validate ... against ISO 4217 standard', but there is no explicit guidance on when to prefer this over siblings like fx_spot_price_oracle or calculate_fx_savings, nor any statement about invalid-input behavior. An agent can infer the context but is given no routing rules.

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