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

Annotations already provide strong safety signals (readOnlyHint=true, destructiveHint=false), which lowers the bar for behavioral disclosure. The description adds useful context by listing return fields, but does not mention any other behavioral traits such as case sensitivity, error handling, or pagination. 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 sentence that immediately states the action, provides an example, and lists output fields. Every word earns its place, with no fluff or repetition.

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 tool with a clear output schema and comprehensive annotations, the description is complete. It covers the core functionality and return values, and the schema handles the parameter details. There are no missing pieces that would prevent correct invocation.

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 coverage is 100%, and the schema documents the 'region' parameter with allowed enum values (africa, americas, asia, europe, oceania). The description's examples ('Africa', 'Europe', 'Asia') are capitalized, which could conflict with the lowercase schema values, creating minor ambiguity. It adds no new parameter meaning beyond what the schema already provides.

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 the action ('List all countries in a region') and the specific resource scope. It distinguishes itself from sibling tools like countries_by_currency and countries_by_language by focusing on region filtering, and mentions the return fields (name, capital, population, area, flag emoji) which adds specificity.

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 gives clear context for when to use this tool (when you need countries by region) but does not explicitly mention alternatives or exclusions. Since there are closely related sibling tools (e.g., countries_by_currency), a brief note about using those for currency-based lookups would elevate it to a 5.

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