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

Discloses reliance on a free API with no key required and ISO code requirement. With no annotations, it covers key behavioral aspects, though lacks mention of response format (mitigated by output schema presence).

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?

Three sentences no redundancy: purpose, technical constraint (API + codes), and usage priority. Highly efficient.

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 exchange rate tool with output schema present, the description covers purpose, data source, code requirements, and fallback guidance—complete for reliable agent invocation.

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 covers all 3 parameters (100% coverage), so baseline is 3. The description adds value by listing example ISO codes and clarifying amount defaults, improving usability beyond schema.

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?

Clearly states it gets the latest exchange rate and converts an amount, specifying the API source and code format. Distinct from sibling tools which are generic arithmetic or date calculations.

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?

Explicitly instructs to use as primary source and fall back to web search only if needed, providing clear when-to-use and alternative guidance.

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