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

Beyond the readOnly/idempotent annotations, the description discloses the return contents (converted amount, per-unit rate, actual rate date), the business-day fallback behavior, and the fact that the tool explicitly reports the true rate date rather than silently using a stale date. It also adds pricing and authentication context. No contradiction with annotations.

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 dense and information-rich, front-loading the main action and then covering returns, caveats, use case, required inputs, pricing, and auth. There is minor redundancy in starting with 'Convert an amount' and then repeating 'Convert between', but every sentence otherwise earns its place.

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 an output schema present, the description covers everything else needed to call the tool correctly: supported currencies, date semantics, business-day behavior, intended use case, required parameters, pricing, and the fact that no wallet or API key is needed. The annotation set and schema already handle safety and return structure.

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 from, to, date, and amount. The description adds the ECB reference-rate context and implies that amount is optional with default 1 only through the schema, not the description. It confirms required inputs but does not substantially enrich parameter meaning 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?

The description opens with a specific verb and resource: 'Convert an amount at the ECB's published rate'. It clearly scopes the tool to 30+ currencies at the ECB daily reference rate for today or any past date, which distinguishes it from price or quote tools among the siblings.

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 explicitly says these are 'reference rates for accounting and reporting, not tradable quotes', giving a clear when-to-use and when-not-to-use signal. It also explains weekend behavior with business-day fallback. It stops short of naming a specific sibling alternative, so it lacks the full explicit alternatives routing of a 5.

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