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

Annotations already establish read-only, idempotent, non-destructive behavior. The description adds valuable context beyond annotations: bounded retrieval, validation, clearly labelled cross-rate calculation, and x402 delivery with a fee. This meaningfully informs the agent about what happens during invocation.

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 tightly written sentences: the first nails the core function, the second adds relevant commercial/sourcing context. Every phrase earns its place with no redundancy or filler.

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?

Given the rich input schema, enums, output schema, and detailed annotations, the description is sufficient. It adds the key non-schema context (data source, fee, delivery mechanism, validation). It does not explicitly mention the optional date parameter, but the schema already covers that thoroughly.

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 the schema already documents amount, currencies, and date semantics. The description adds only general context ('supported currencies', 'amount') but no parameter-level detail beyond what the schema provides, which matches the baseline for high schema coverage.

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 the action ('Convert an amount'), the specific resource ('ECB daily reference-rate observation'), and the scope ('between two supported currencies'). This distinguishes it from generic converters like data.convert and other sibling tools.

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 makes the tool's purpose clear and implies its use for ECB-reference-based currency conversion, but it does not explicitly state when to prefer this over alternatives or provide exclusions. The context is clear, yet no alternatives or when-not-to-use guidance is offered.

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