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

Annotations already declare the tool as read-only, idempotent, and non-destructive. The description complements this by noting the data is 'one record per day (end_of_day)' and cites the source, adding behavioral context beyond the annotations without any contradiction.

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 extremely concise—two sentences that immediately state the tool's purpose, data source, and key usage instruction. Every word adds value, with no filler or repetition.

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?

The description does not explain the output format or list specific return fields, which is a gap given the absence of an output schema. However, the tool's nature (daily exchange rates) allows an agent to infer typical fields (currency pair, rate, date). It provides enough context for basic usage but lacks completeness on response 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?

The input schema has 100% description coverage for all 8 parameters, with examples and detailed descriptions. The tool description only repeats the usage of 'from/to' but does not add new meaning beyond what the schema already provides. Baseline score of 3 is appropriate.

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 clearly identifies the tool as retrieving HKD market exchange rates against major currencies, specifies daily frequency (end_of_day), and references the data source. This distinguishes it from sibling tools like hkma_interbank_interest_rates which deal with different financial data.

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 instructs users to 'Use from/to to window the dates,' providing direct guidance on parameter usage. While it does not list alternative tools or when-not-to-use scenarios, the sibling list implies other HKMA tools for different datasets, making the usage context sufficiently clear.

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