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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds useful domain context—that results include country/region codes and that regions like Europe or Global cover many countries—which helps an agent interpret and use the output. Minor gaps like pagination or result ordering remain, but the annotation bar is lower.

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 sentences, front-loaded with the core action and followed by a useful clarification about regions. Every sentence earns its place with no padding.

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 zero parameters and no output schema, the description does a good job explaining what is returned and the region concept. It could mention whether the full list is returned at once or if there is ordering, but for a simple catalog tool this is largely complete.

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 takes zero parameters, and the rule sets a baseline of 4 for that case. There is nothing for the description to compensate for beyond the empty schema.

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 country and region we sell eSIM data plans for, with their codes'), making the tool's output clear. It implicitly distinguishes itself from plan-search siblings like search_esim_plans by focusing on destinations, not plans, but never names an alternative explicitly.

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?

Usage is implied: an agent can infer this tool provides a catalog of destinations to browse or reference before searching plans. However, the description gives no explicit when-to-use, when-not-to-use, or alternative-tool guidance (e.g., no mention of search_esim_plans).

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