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

Given no annotations, the description discloses the paid nature ($0.002 per call) and the two-step payment process via x402. This is good behavioral transparency, though it does not mention rate limits or idempotency.

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?

Two sentences with core purpose first, then payment details. Efficient and front-loaded, but could be slightly more structured.

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?

Covers the source (ECB) and payment, but lacks details on output format, which is important given no output schema. Also missing typical usage scenarios.

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 baseline is 3. The description adds that 30+ currencies are supported, but does not provide additional semantic context beyond what is 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 tool retrieves current and historical foreign exchange rates from the European Central Bank, with support for 30+ currencies. This is a specific verb-resource pair and distinguishes it from sibling tools like 'convert_currency'.

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?

No guidance on when to use this tool versus alternatives. It describes the payment process but does not compare with other currency-related tools or specify use cases.

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