Historical FX rate on a date

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

Annotations already declare readonly, idempotent, non-destructive. The description adds the critical fallback behavior for weekends/holidays, which is not implied by annotations. No 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?

Single sentence with key information front-loaded: purpose, date format, and fallback. No unnecessary details.

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 historical rate tool with strong annotations and clear schema, the description covers essential behavior (fallback). Absence of output schema is acceptable as return structure is standard.

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 67% with most parameters described. The description does not add meaning beyond schema for 'base' or 'symbols'. Baseline 3 is appropriate as description does not improve parameter understanding.

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 the tool retrieves FX reference rates for a specific past date, with date format and fallback behavior. It distinguishes from sibling tools like fx_latest_rates and fx_timeseries by specifying 'historical' and 'past date'.

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 implies usage for single historical date queries with fallback. It does not explicitly exclude other uses, but sibling names provide contrast. No when-not-to-use guidance is given.

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