get_historical_rates

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

Without annotations, the description carries the burden of behavioral disclosure. It reveals the API key requirement and period granularity (hourly, daily, weekly) but omits details on error handling, rate limits, or authentication failure 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?

The description is two sentences long, front-loads the primary purpose, and efficiently covers period details and API key requirement. No wasted words.

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 with 3 parameters and no output schema, the description covers the core purpose, period mapping, and authentication need. It does not describe the return format, but the information is sufficient for an agent to decide whether to invoke the tool.

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. The description adds value by mapping period values to granularity (1d=hourly, etc.), but for source/target it merely restates schema info. The addition is marginal.

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 states 'Get historical exchange-rate data points for a currency pair over a period,' clearly indicating the verb (get) and resource (historical exchange-rate data points). It distinguishes itself from siblings like get_exchange_rate (likely current rate) and list_currencies by focusing on historical data, though no explicit sibling differentiation is provided.

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 explains when to use the tool (for historical data over a period) and mentions a prerequisite (API key), but it does not specify when not to use it or mention alternative tools like get_exchange_rate for current rates.

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