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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds valuable behavioral context: 'updated on ECB working days,' 'unsupported currencies fail closed,' 'FREE — no payment required,' and the exact return format. This exceeds what annotations provide and gives the agent a clear model of expected behavior.

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 efficiently structured in two short paragraphs: the first delivers the core action, and the second covers usage context, update frequency, failure mode, cost, and return value. Every sentence earns its place with no redundancy or fluff.

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 two-parameter, read-only tool with strong annotations and no output schema, the description is comprehensive. It explains the source (ECB), freshness, failure behavior, cost, return format, and a clear usage scenario. No important information is missing for an agent to select and invoke this 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?

The input schema fully documents both parameters with descriptions and examples, covering 100% of the parameters. The description adds a partial list of supported currencies and the fail-closed behavior, but does not add meaningful meaning beyond the schema. Baseline 3 is appropriate because the schema does the heavy lifting.

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 opens with a specific verb+resource: 'Get the current certified ECB reference rate between two supported currencies.' This clearly states the tool's function and distinguishes it from all shipping-related sibling tools, none of which handle currency exchange. It also provides a concrete use case for shipping cost conversion.

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 explicitly states when to use the tool: 'Use this to normalize costs from different carriers/countries to a common currency for comparison.' It also notes the update frequency and fail-closed behavior. However, it does not explicitly mention when-not to use it or name alternatives, though no sibling tool performs FX conversions.

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