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

The description provides crucial operational context beyond the structured data, specifically the pricing model ($0.002 per successful call) and the specific condition under which charges apply ('failed calls are not charged'). This is highly valuable behavioral information.

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 somewhat dense due to the inclusion of pricing details, but it remains focused and addresses all necessary points in a single, structured block.

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 the full schema coverage and the inclusion of pricing and data scope, the definition is comprehensive for an AI agent needing to decide if this specific tool is appropriate for a query.

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?

Since schema description coverage is 100%, the baseline score is 3. The description merely reinforces the usage of the 'id' field to accept both symbols and names, which is already detailed in 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 clearly identifies the purpose as providing exchange rates against the USD. It specifies the scope (170 fiat, 400+ crypto) and the types of currencies included, making it easy for an agent to understand its domain.

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?

Usage guidance is implied through the parameters—specifying symbol, name, or type—but it does not offer explicit recommendations on when to choose this tool over other rate-fetching siblings.

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