List supported cities by country

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

Annotations already indicate read-only, non-destructive, and idempotent behavior. The description reinforces this by stating 'Read-only, no side effects' and adds that it returns both a text summary and structured JSON. This adds value beyond annotations.

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?

Two concise sentences: first states purpose, second provides usage guidance and behavioral note. Front-loaded with key information, no wasted words.

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 simple tool (one optional parameter) and rich annotations, the description covers the essential aspects. It mentions what to call first and the return format, though it doesn't detail the structured JSON format. Sibling tools are listed but not contrasted, but the purpose is sufficiently clear.

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 already provides a detailed description of the 'country' parameter (case-insensitive, canonical names, examples). The tool description merely paraphrases this as 'optional country filter narrows to one country,' adding minimal additional meaning. With 100% schema coverage, baseline is 3.

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 tool lists all city slugs grouped by country, and that it should be called first to discover valid slugs. This explicitly identifies the verb, resource, and context, and distinguishes it from sibling tools that perform different tasks like comparing or summarizing cities.

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 explicitly directs the agent to call this tool first to discover valid slugs before using other tools. It also mentions the optional country filter. While it does not explicitly state when not to use it, the context is clear that it is the discovery entry point.

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