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

Annotations already declare readOnlyHint=true, destructiveHint=false, idempotentHint=true, and openWorldHint=true, which signal this is a safe, read-only operation. The description adds the context of being 'official' and 'reference' rates, but does not disclose additional behaviors such as rate limits, data freshness, or response structure. Since annotations cover the safety profile, the description adds moderate value.

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?

The description is a single sentence that is informative and to the point. It includes the verb, resource, scope, and data source without any redundant information. Every word serves a purpose.

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 simple retrieval tool with comprehensive annotations and a full input schema, the description is sufficiently complete. It states the source, scope, and purpose. The presence of an output schema (as per context signals) means return values do not need description. However, it could mention that the date parameter is for historical rates (though covered in schema) or provide a note on rate limiting, but overall it meets the needs.

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?

The input schema has 100% description coverage for all three parameters, so the schema already documents the parameters adequately. The description mentions '~33 currencies' which aligns with the schema's maxItems constraint, but does not add any additional semantic meaning beyond what is in the schema. Baseline score of 3 is appropriate.

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 clearly states that the tool retrieves official ECB reference exchange rates for ~33 fiat currencies. It uses a specific verb ('Get') and resource ('ECB exchange rates'), and explicitly mentions the data source (Frankfurter/ECB), distinguishing it from other exchange rate tools like 'currency.exchange.latest' or 'finance.currency.rates'.

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?

The description implies the tool should be used for obtaining official ECB rates, but it does not explicitly provide when to use it versus alternative exchange rate tools (e.g., 'currency.exchange.latest'). There is no guidance on exclusions or prerequisites, leaving the agent to infer usage context from the tool name and title alone.

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