List supported countries

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

With no annotations, the description must disclose behavioral traits. It states the tool distinguishes EU from non-EU countries, which is helpful, but it does not clarify the output format (e.g., names, codes) or whether non-European countries are included. Missing details like response structure or potential limitations.

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 concise sentences, front-loading the core purpose and adding a key distinction. Every sentence adds value without redundancy.

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?

No output schema is provided, so the description must explain return values. It mentions a list of countries with a distinction between EU and non-EU, but it does not specify the exact format (e.g., ISO codes, names), whether non-European countries are included, or the structure of the response. This leaves ambiguity.

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 tool has no parameters and 100% schema coverage. The description does not need to add parameter info, so baseline score of 4 is appropriate.

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 that the tool returns a list of countries with VAT data from the vatnode MCP server, and it distinguishes between EU member states and other European jurisdictions. This is specific and differentiates the tool from siblings like list_eu_vat_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 implies usage when you need to know supported countries, but it does not explicitly state when to use this tool over siblings like get_country_vat_rates or check_vat_format. No when-not or alternative guidance is provided.

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