get_fx_rate

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

Discloses return null if no rate found, USD returns 1.0, fallback up to lookback_days, and cache prerequisite. No annotations provided, so description adequately covers behavior.

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 concise sentences with no waste. Front-loaded with purpose, then details. Every sentence adds value.

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?

No output schema or annotations, but description explains return values (null, 1.0), fallback, and prerequisite. Missing explicit output format (e.g., number) but is sufficient overall.

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 100% of parameters with descriptions. Description adds context for USD behavior and fallback, but does not significantly extend 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?

Description clearly states verb 'look up', resource 'historical FX rate', and specifics: from local cache, foreign per USD, USD always 1.0, fallback behavior. Distinguishes from other tools like sync_fx_rates.

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 advises to run sync_fx_rates first, and explains fallback with lookback_days for weekends/holidays. Lacks explicit when not to use, but context is clear.

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