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

Annotations already declare readOnlyHint=true, openWorldHint=true and destructiveHint=false, so safety is covered. The description adds real value beyond that: it names the ECB rate source and warns that TWD (despite being listed as supported) returns null, which prevents a silent misinterpretation. It stops short of describing rate freshness/timestamp or how cross rates are derived.

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?

Three short sentences, front-loaded with the core action, followed by the value domain and the one caveat. Every clause carries information an agent needs; nothing is redundant.

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?

An output schema exists, so return shape need not be explained, and the description still flags the null case for TWD, which is the one output-related trap. What remains unstated is the rate timestamp/date basis and whether the default amount of 1 yields a straight rate lookup, both minor for a 3-parameter tool.

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 coverage is 100%, so the baseline would be 3, but the schema defines `from`/`to` as bare strings with zero enums. The description supplies the actual value domain (USD, CNY, EUR, JPY, GBP, CAD, AUD, HKD, TWD, KRW), which is meaning the schema does not carry at all.

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?

States a specific verb and resource ('Convert an amount between currencies') plus the rate source (ECB reference rates). No sibling tool in the list performs conversion, so the distinction is unambiguous, and the supported-currency list further pins down scope.

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?

Usage is clear from the purpose and there is no competing sibling to route against, so no alternatives section is needed. It also sets a hard precondition by enumerating which currencies can be passed, which effectively tells the agent when the call is invalid.

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