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

Annotations already disclose readOnlyHint=false, openWorldHint=true, idempotentHint=false, and destructiveHint=false. The description adds crucial behavioral context not in the annotations: the exact cost ($0.002 in USDC on Base per successful call) and payment protocol (x402), plus the data source (ECB) and what the response contains (rates, converted amounts, applicable date).

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 what the tool does, followed by usage guidance and cost information. It is efficient with no redundant sentences, though the cost sentence could be considered slightly separate from the core purpose.

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?

With no output schema, the description explains the return values (rates, converted amounts, date the rates apply to) and the payment model. Annotations cover the safety profile, and the description fills in the remaining behavioral and data-source details. An agent has everything needed to call the tool correctly.

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 description coverage is 100%, so the input schema already documents all three parameters thoroughly. The description restates that a base currency is required and target currencies and amount are optional, but adds no new semantic detail beyond the schema (e.g., no format hints or default behavior clarification beyond what is already 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 states the resource (foreign exchange rates from the ECB for ~30 major currencies) and the operation (give base currency, get rates and converted amounts). It does not explicitly distinguish itself from any sibling tool, though its domain is unique among the provided 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?

It gives clear usage contexts: 'Use for currency conversion, invoice and price calculations, and reporting in another currency.' It does not state when not to use the tool or name any alternatives, but it provides enough context for an agent to select it confidently.

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