List countries

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

With no annotations, the description carries the full burden of behavioral disclosure. It states that no API key is required and that the operation lists all supported countries, which implies a non-destructive read. However, it does not mention pagination, response envelope, rate limits, or any caveats; for a simple zero-parameter list tool this is adequate but not rich.

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 that states the action, scope, returned fields, and auth requirement with no wasted words. It is appropriately sized for the simplicity of the tool and every part earns its place.

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 zero-parameter tool with no output schema and no annotations, the description covers the core what, scope, and auth requirement. The main gap is the relationship to the sibling get_service_countries, but the 'all supported countries' phrasing provides enough global context for most agents to use the tool 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?

The input schema is an empty object with no parameters, so the description cannot add parameter-level meaning. The zero-parameter case calls for the baseline 4; the description's mention of returned fields is informative but not about parameters.

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 a specific verb ('List') and resource ('all supported countries'), and specifies the returned fields (flags and ISO codes). It does not explicitly differentiate itself from the sibling get_service_countries, though 'all supported countries' hints at a global scope. Because the differentiation is only implied rather than stated, it stops short of a 5.

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?

There is no guidance about when to choose this tool over alternatives such as get_service_countries or list_services. 'No API key required' is an access note, not a selection criterion, and no exclusions or conditions are provided. This leaves the agent to infer the appropriate context on its own.

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