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

Annotations already declare read-only, idempotent, closed-world, and non-destructive behavior, so safety is covered. The description adds that it 'walks through the check on iPhone and Android,' indicating a platform-specific guide format, but does not disclose further behavioral details such as output format or limitations.

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 with no wasted words. The usage condition is front-loaded, followed immediately by the platform-specific detail.

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 check with an output schema and rich annotations, the description provides sufficient context: what it checks, why it matters, and what platforms it covers. Nothing critical is missing.

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, so the schema itself has no semantic burden. The description correctly adds no parameter details, and the baseline for zero-parameter tools is 4.

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?

States a specific verb and resource: 'check whether their phone is carrier-unlocked.' The mention of travel eSIMs gives context, but it does not explicitly differentiate from sibling tools like check_device_compatibility or troubleshoot_esim.

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?

Opens with 'Use when the user needs to check...' which clearly identifies the triggering scenario. It does not name alternative tools or conditions where a different check would be more appropriate, so it stops short of full when-not guidance.

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