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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering safety. The description adds useful context by explaining what perUsd means. It does not disclose which currencies are included or response format, but these are minor given the tool's simplicity.

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 a single sentence with no filler and places the purpose first, followed by the precise unit definition. Every word contributes to the agent's understanding.

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 parameterless, read-only, idempotent tool, the description is nearly complete: it explains the tool's purpose and rate semantics, while annotations cover safety. It omits details like currency coverage or staleness, but these are not essential for correct invocation.

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?

With zero parameters, the schema is empty and the baseline is 4. The description adds meaning by explaining that the rates are used to convert USD prices, which is the only context needed for a parameterless tool.

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 tool as providing exchange rates for converting USD prices, and it defines the unit semantics (perUsd = units of currency per 1 USD). This makes the resource unambiguous. It does not explicitly differentiate from siblings, but the domain is distinct enough from the model/price-related siblings.

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 phrase 'used to convert USD prices' provides a clear context for when this tool should be invoked. It does not mention alternatives or exclusions, but for a parameterless lookup tool the use case is sufficiently specified.

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