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

With no annotations, the description must carry the behavioral burden. It usefully discloses that calls cost 0.005 USD via x402 and that the rates are current, but it does not describe return format, pagination, rate limits, or whether there are any access constraints for the x402 payment flow.

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 two sentences and front-loads the core value: current EU VAT rates by category. The scope and pricing details follow without waste, and every sentence contributes necessary information.

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 simple one-parameter lookup tool with no output schema, the description is largely complete: it names the rate categories, notes category notes are included, and explains the country/all scope. The main remaining gap is the absence of any return-value structure, though this is less critical for a straightforward lookup.

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%, and the single parameter is already documented as 'ISO alpha-2, omit for all EU'. The description reinforces this with 'One country or all' but adds no additional parameter semantics beyond 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 resource and content: current VAT rates for EU member states, including standard, reduced, super-reduced, and parking rates with category notes. It does not explicitly distinguish itself from the sibling eu_vat_check, so the differentiation is implied by 'rates' versus 'check' rather than stated.

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 'One country or all' gives basic usage scope, indicating the tool can be called for a single country or across the EU. However, it does not state when to use this tool versus alternatives such as eu_vat_check, nor does it mention exclusions or prerequisites beyond the pricing note.

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