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

Annotations already declare this as a safe, idempotent read operation. The description adds useful behavioral context beyond annotations by identifying the data source as the manufacturer's published list, noting regional exceptions such as mainland China models, and indicating that a source link is returned.

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?

It is a single front-loaded sentence with no wasted material. The parenthetical regional-exception note is relevant and compactly presented.

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 one-parameter, read-only lookup tool with full annotation coverage, the description supplies the key missing context: data provenance, regional caveats, and the fact that a source link is included. Nothing essential for correct invocation is absent.

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%, so the baseline is 3. The description adds meaning by clarifying that the model parameter covers phones, tablets, and watches, whereas the schema examples only mention phone models.

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 and resource: checking whether a phone, tablet, or watch model supports eSIM. It also distinguishes the tool from sibling plan/provider tools by focusing on device compatibility and naming the authoritative source.

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 context is clear: use this when verifying eSIM support for a specific device model. It does not explicitly state when not to use it or name alternatives, but no sibling tool serves the same purpose, so the routing gap is minimal.

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