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

Annotations already cover read-only, idempotent, non-destructive behavior; the description adds meaningful context beyond them: ECB sourcing, cross-rate calculation via EUR, return fields of rate/date/source, the non-trading-quote caveat, and a $0.005 USDC per-call x402 price.

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 front-loaded with the core purpose and source, then adds only useful constraints and pricing. Every sentence earns its place without padding.

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?

There is no output schema, but the description states what is returned: the rate, its date, and source. It also covers data source, currency coverage, pricing, and the reference-rate caveat; the remaining gap is detailed parameter behavior.

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?

With schema description coverage at only 33%, the description partially compensates by listing supported currencies and mentioning the amount and cross-rate method. However, it never explains the from/to code format, the comma-separated or "all" behavior of to, or the default amount.

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?

Opens with a specific verb and resource: converts currency amounts using official ECB euro reference rates. It names the data source and 30-currency scope, which clearly distinguishes it from generic conversion siblings like unit_convert.

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 clearly frames the use case as reference-rate conversion rather than trading quotes, giving an important usage boundary. It does not explicitly name alternatives such as unit_convert or state exclusions, so it falls short of full routing guidance.

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