get_historical_rates

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

With no annotations, the description carries the behavioral burden. It discloses that sampling is fixed per period (1d=hourly, 7d/30d=daily, 1y=weekly), the window always ends NOW, and it provides the return shape. It does not mention rate limits or auth, but for a read-only historical data tool the disclosed behavior is substantial and accurate.

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 front-loaded with the primary use case, followed by the return format, key behavioral constraints, and sibling routing. Every sentence earns its place and there is no filler or redundancy.

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?

Even without an output schema, the description gives the full return structure, sampling rules, window semantics, and explicit alternative tools. Combined with fully documented parameters, an agent has everything needed to call this tool correctly in the intended scenarios.

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% and the schema already describes source, target, and period in detail, including defaults and exact point counts. The description mostly restates the period sampling behavior and adds use-case flavor, but does not add significant new meaning beyond the 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?

The description names a specific operation ('get historical rates') with a clear resource and scope: fixed-window time-series. It gives concrete example queries and explicitly distinguishes itself from sibling tools, so an agent can tell exactly what this tool does without inspecting others.

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 states exactly when to use this tool ('fixed-window time-series questions') and when not to: use get_rates for specific past datetimes or custom ranges, and get_exchange_rate for a single live rate. This explicit routing to alternatives leaves no ambiguity.

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