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

With no annotations provided, the description carries the burden of behavioral disclosure. It discloses the approximate one-year range limit and implies a series of exchange rates, but it does not cover other behavioral details such as output structure, rate limits, or handling of invalid date ranges. This is adequate but not rich.

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 a single, front-loaded sentence that communicates the tool's purpose, its primary use case, the date range limit, and the input requirements without any filler or redundancy. Every part earns its place.

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 simple read-only tool with fully documented parameters, the description covers the core operational details: purpose, date range, input formats, and target currencies. There is no output schema, so the response shape is not specified, but the phrase 'time series' gives a reasonable expectation of the return concept.

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%, so the baseline is 3. The description reinforces that start and end are YYYY-MM-DD and that one or more target currencies are needed, but it does not add meaning beyond what the input schema already documents, such as the comma-separated format or the default base currency.

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 states a specific action: retrieving a time series of exchange rates for a base currency over a date range. It also adds the use case of trend analysis, which helps distinguish it from a simple conversion or currency-list tool, though it does not explicitly contrast with the similarly named fx_historical or fx_rates siblings.

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 gives clear context for when to use the tool: for trend analysis over a date range of roughly up to one year. It does not explicitly mention alternatives or exclusions, but the stated use case is sufficient for an agent to select it appropriately in most situations.

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