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

Annotations already declare readOnlyHint and openWorldHint, so safety and network access are covered. The description does add one genuinely useful behavioral trait beyond them: the rate used is the last published ECB rate on or before the requested date, which tells the agent how weekends and holidays are handled. It does not mention rounding/precision or that ECB rates are EUR-based (so cross rates are triangulated), which matters for a conversion tool.

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?

One short sentence with no filler. It is grammatically a fragment rather than a front-loaded action statement, which slightly weakens the opening, but nothing is wasted.

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 four required parameters, no output schema, and no nested objects, the tool is simple, and the description helpfully discloses the two return values (rate and converted amount). It still leaves gaps a caller would care about: rounding behavior and what happens with unsupported or non-ECB currencies.

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% and every parameter carries its own description, so the schema does the heavy lifting. The description adds no meaning beyond it — no note on currency-code casing handled by the pattern, no note on how fractional amounts are treated.

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 names the specific resource (ECB reference rate) and the outcome (the converted amount), so an agent can infer conversion of an amount between two currencies. It lacks an explicit action verb — the sentence is a noun phrase — and offers no differentiation from the two receipt-oriented siblings, though the domain gap makes that less critical.

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?

There is no statement of when to use this tool, no prerequisites, and no mention of alternatives such as the sibling receipt tools. An agent must infer from the parameter list that this is the conversion step in a receipt workflow.

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