exchangerate_historical

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

With no annotations provided, the description carries the full burden. It discloses that an API key is required, which is a critical behavioral trait. However, it does not mention other traits like rate limits, error handling for invalid dates, or that it is a read-only operation (though implied). The disclosure is 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?

The description is extremely concise (two sentences), front-loaded with the purpose first, and every sentence earns its place. No extraneous information.

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?

Given that there is no output schema and no annotations, the description is insufficiently complete. It does not explain the returned data format, valid date ranges, or the role of the optional 'base' parameter (though the schema states default USD). For a tool with 5 parameters and no output schema, the description should provide more context.

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?

The input schema has 100% coverage with descriptions for all 5 parameters. The description adds no additional meaning beyond what the schema already provides, so a baseline score of 3 is appropriate.

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 clearly states the tool's purpose: 'Get historical exchange rates for a specific date.' This distinguishes it from sibling tools like exchangerate_latest (current rates) and exchangerate_convert (conversion). The verb 'get' and resource 'historical exchange rates' are specific.

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 implies that the tool should be used when historical rates for a past date are needed, but it does not explicitly exclude other use cases or mention alternatives (e.g., 'use exchangerate_latest for current rates'). The context is clear but lacks explicit when-not guidance.

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