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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds valuable behavioral context: it is a 'Premium API' with a specific cost ($0.25 USDC via x402), which is important for an agent deciding whether to invoke a paid tool. It also discloses the breadth of the lookup (country name, ISO code, city, or address) and the richness of the response categories.

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 purpose before adding cost and scope details. Every sentence earns its place: the first defines the tool's function and scope, the second discloses the premium cost. It is slightly dense with the long list of categories, but that list is genuinely useful for distinguishing the tool's output.

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 single-parameter read-only lookup tool with no output schema, the description is quite complete. It covers what the tool returns (VAT rates by category, thresholds, exceptions), the geographic scope, and the cost. The only minor gap is that it doesn't describe the exact response format, but with no output schema and a simple lookup parameter, the description provides enough for an agent to call it 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 schema already documents the 'lookup' parameter well, including examples. The description adds meaning by clarifying that the lookup accepts country name, ISO code, city, or address, and by explaining what the returned data will contain (category breakdown, thresholds, exceptions). This goes beyond the schema's minimal 'Country name, ISO code, city, or address'.

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 states a specific verb ('Retrieve'), a clear resource ('current VAT rates for any European country'), and a detailed scope (EU-27, EEA, UK, Switzerland, non-EU Europe). It also lists the category breakdown (standard, reduced, super-reduced, zero-rated, exempt) plus registration thresholds and territorial exceptions, which distinguishes it from sibling tools like interzoid_sales_use_tax_rates or interzoid_customs_duty_rates.

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 clearly implies when to use this tool: when European VAT rates are needed, and the scope statement helps an agent select it over tax-related siblings. It does not explicitly name alternatives or state when not to use it, but the geographic and category specificity provides strong contextual guidance.

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