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

Annotations already state this is a read-only, idempotent, non-destructive, closed-world helper, so the safety profile is covered. The description adds that the tool explains line assignment for data, calls, and iMessage and how to avoid roaming charges, but it does not disclose any additional behavioral traits such as whether it inspects the device or what form the guidance takes. A 3 is appropriate because it adds useful scope but no new behavioral caveats 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 sentences, front-loaded with the use case, and no filler. Every clause tells the agent when to use the tool and what it covers.

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?

Output schema exists and annotations cover safety, so return values and safety need not be described. The description states the user scenario and topics explained, making it complete enough for a simple informational helper. It stops short of routing to alternatives among the many sibling tools, so 4 rather than 5.

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% and the only parameter primary_use is fully described in the schema, so the schema carries parameter semantics. The description does not reference primary_use or add syntax/examples beyond the schema. Baseline 3 for high coverage with no additional param meaning.

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 scenario and content: home line plus travel eSIM configuration, explaining which line handles data, calls, and iMessage, and roaming avoidance. It distinguishes from generic eSIM troubleshooting and plan tools by focusing on dual-SIM line assignment, though it does not name a sibling.

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 first sentence gives an explicit when-to-use condition: home line plus travel eSIM and needing the right configuration. It implies but does not state exclusions or name alternatives like troubleshoot_esim or get_installation_guide, so 4.

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