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

With no annotations, the description carries the full behavioral burden. It usefully discloses the authoritative rate source (臺灣銀行牌告匯率, 現鈔/即期), which an agent could not infer otherwise. However, it says nothing about whether rates are live or cached, error behavior for unknown currencies, or what the response contains.

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?

A single compact sentence with the operational core front-loaded after the context tag. The bracketed travel prefix is mild filler but sets scope efficiently; no sentence 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?

For a 4-parameter tool with no annotations and no output schema, the description covers the rate source, direction, and instrument type but omits the currency-code format, amount constraints, and what the computed result looks like. Adequate but with clear gaps.

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 0%, so the description must compensate. It does this well for the two enum parameters by defining the semantics the enums lack: buy = TWD→foreign, sell = foreign→TWD, and cash vs spot. It adds little for cur/amount, though those are largely self-evident.

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 a specific verb+resource (試算換匯 using Bank of Taiwan posted rates) and clarifies the direction semantics, which cleanly distinguishes it from the sibling trip__exchange_rates that presumably just lists rates. It stops short of explicitly naming that sibling, so differentiation is inferred rather than stated.

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 bracketed travel context implies when the tool is useful, but there is no explicit when-to-use vs when-not guidance and no mention of the alternative trip__exchange_rates for simply viewing rates. Usage must be inferred from the travel framing.

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