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

The description adds the behavior of returning all rates if no code is given, but this directly contradicts the schema's required field 'code.' It does not disclose other behavioral traits such as output format or date usage, and the contradiction with the schema undermines transparency beyond what annotations provide.

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 short and front-loaded, but the second sentence includes a statement ('or all rates if no code given') that is misleading given the required 'code' parameter. This prevents it from being concise in a useful way—it introduces confusion rather than earning its place.

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 simple tool with full schema coverage and readOnly annotation, the description covers the core lookup behavior. However, it fails to explain the output format, the handling of the optional date, or resolve the contradiction about missing code. Overall it is minimally adequate but has clear gaps.

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% with both parameters ('code' and 'date') already described in the input schema. The description does not add additional meaning about parameters beyond what the schema provides, so the 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 this is a single-currency lookup for the CZK rate, using a specific verb ('Get') and resource (CZK rate). It distinguishes from the sibling get_rates by emphasizing 'single-currency,' though the added 'or all rates if no code given' introduces confusion and overlaps with get_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?

The description implies usage for quick single-currency lookups, but it does not explicitly mention when to use this tool versus alternatives like get_rates or convert. The phrase 'if no code given' suggests an alternative usage that contradicts the schema, making the guidance unclear and potentially misleading.

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