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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds only the latest-vs-historical-date behavior, which the schema's date property already states, and says nothing about rate source, rounding/precision, or network failure behavior for an open-world lookup.

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 front-loaded sentence covering purpose, date behavior, and code format, followed by a compact example. The example duplicates the schema's examples array, which is mild waste but not disruptive.

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, so the description should indicate what comes back — converted amount, applied rate, effective date — for an agent to use the result correctly. It also omits error behavior for invalid currency codes or unavailable historical dates, leaving a real gap for an open-world lookup 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 all four parameters are already documented in the schema, including the date format and amount default. The description only reinforces the ISO three-letter code convention and repeats an example that already appears in the schema's examples array, so it adds little beyond the structured data.

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 states a specific verb (换算) and resource (两种货币金额/汇率), and adds the ISO three-letter code constraint, so an agent knows exactly what it does. It does not, however, distinguish itself from the sibling exchange_rate or unit_convert, leaving the agent to infer the boundary.

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 only implied: converting an amount at the latest or a historical date. There is no explicit when-to-use or when-not-to-use guidance, and no mention of when to pick this over exchange_rate (rate lookup) or unit_convert (non-currency units).

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