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

No annotations are provided, so the description must carry the behavioral disclosure. It states the return structure {rates, date, source}, which is helpful. However, it does not explicitly mention that it is a read-only, idempotent operation or any potential side effects, leaving room for slight ambiguity.

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?

Two short sentences: first states purpose, second provides parameter format and return structure. Every word earns its place; no superfluous content.

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?

Given the tool's simplicity (1 optional param, no output schema), the description completely covers what an agent needs: purpose, parameter format, and return format. No gaps remain.

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 schema only defines the 'date' parameter as string|null with no description. The description adds significant meaning: 'date format: YYYYMMDD or None for today.' This fully compensates for the 0% schema description coverage.

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 official NBU exchange rates. The verb 'Get' and resource 'exchange rates' are specific. Siblings like geocode_ukraine, get_weather_ukraine, etc., are clearly distinct.

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 provides the date format and default behavior (None for today). While it doesn't explicitly state when to use vs alternatives, the simplicity and distinct sibling names make the usage clear.

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