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

With no annotations provided, the description carries the behavioral disclosure burden. It does disclose that the tool works offline and only validates country format, which is useful transparency. It does not explain edge-case behavior such as empty input, normalization, or what result is returned for invalid formats.

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 a single front-loaded sentence with no filler or redundancy. Every word contributes meaning, and the key qualifier 'offline' directly shapes expected behavior.

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?

Given the tool's low complexity, the description conveys the core operation and offline nature adequately. It lacks concrete input examples and normalization guidance, and an output schema exists but is not described in enough detail to fully compensate for those gaps.

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 parameter 'q' has no schema description and 0% coverage, but the tool description clearly implies that 'q' is the EU VAT number to validate. The description partially compensates for the missing schema documentation, though it never explicitly labels the parameter or states expected formatting (e.g., country prefix, uppercase, spaces).

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 uses a specific verb ('Validate') with a clear resource ('EU VAT number') and scope ('country format', 'offline'). This makes the tool's purpose immediately identifiable and distinct from sibling tools by domain and operation.

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 'offline' qualifier implies this is a local format check rather than a live VAT registration lookup, which gives some usage context. However, there is no explicit statement about when to use this tool versus alternatives or when not to use it.

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