list_regions

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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the agent knows this is a safe, read-only operation. The description adds the detail that it returns all Points of Presence, but doesn't disclose return format, ordering, or whether the list is exhaustive. With annotations covering the safety profile, a 3 is appropriate.

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 and resource without any wasted words. It is appropriately sized for a zero-parameter list tool.

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, read-only list tool with annotations covering safety, the description is nearly complete. It could mention the return format (e.g., array of region objects), but the absence of an output schema and the simplicity of the tool make this a minor gap. The description fully explains what the tool does.

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 zero parameters, so the schema provides no parameter semantics to clarify. The description doesn't need to explain parameters, and the baseline for 0 params is 4. The description's focus on the resource being listed is sufficient.

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 states a specific verb ('List') and resource ('every Point of Presence (region/data-center location)'), and clarifies the purpose: showing where VPS instances can be deployed. This clearly distinguishes it from sibling tools like list_vps or list_os_images, which list different resources.

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 context: call this when you need to know available deployment regions for VPS instances. It doesn't explicitly name alternatives or exclusions, but the resource is specific enough that an agent can infer when to use it versus other list tools. A clear context is provided, though no explicit when-not-to-use guidance is given.

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