get_historical_rates

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

Discloses data source and fallback behavior, which is valuable for an agent. However, no annotations exist, and the description does not cover rate limits, authentication details, or data freshness. Adequate but not comprehensive.

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 sentences, no unnecessary words. Front-loaded with the primary purpose, then adds fallback detail. Highly concise and 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 tool fetching historical rates, the description covers source behavior and scope. No output schema, but parameters are fully documented. Lacks mention of output format or error scenarios, but overall complete for moderate complexity.

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 100%, so baseline is 3. Description adds 'mid-market rates' and 'over the past N days', but does not add additional meaning beyond the schema fields which already describe 'from', 'to', 'days' with constraints.

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 'fetches daily mid-market rates for a currency pair over the past N days'. Distinguishes from siblings like get_rate (single rate) and rate_chart (likely charting). Specific verb+resource+scope.

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?

Mentions fallback behavior (Xe vs Frankfurter) which helps agents decide based on credentials, but does not explicitly state when to use this tool over siblings or when not to use it.

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