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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description's real contribution is output semantics: four possible verdicts (yes / depends / no / unknown), an accompanying note, and the two concrete checks the traveller must perform (dial *#06# for an EID, confirm the phone is not carrier-locked). That is meaningful behavior disclosed beyond the structured fields, though it stops short of explaining what 'depends' hinges on or how to act on each verdict.

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?

Everything is packed into one front-loaded sentence with no filler, and the enumeration of verdicts plus the two checks all earn their place. The clause 'with a note and the two checks to do on the phone' is compressed to the point of slight ambiguity, which keeps it from a 5.

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?

With no output schema, the description does the necessary work of telling the agent what comes back (verdict, note, checks) while annotations handle safety and the schema handles inputs. For a single-required-parameter lookup tool this is close to complete; only the meaning of the 'depends' verdict and recommended next steps are left unstated.

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 both the device and context parameters are already fully documented in the schema, including the expected free-text format for device. The description's 'from its model name' merely echoes that, adding no parsing rules, normalization hints, or examples. Baseline 3 is appropriate when the schema carries the parameter burden.

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 names the exact resource (the traveller's phone / eSIM support) and the operation (determine compatibility from the model name), and it even enumerates the four verdicts it can return. An agent can distinguish this from coverage_check, which is about network coverage rather than device capability. It falls short of a 5 only because the sentence opens with a noun clause ('Whether...') rather than a clean verb, and it never explicitly contrasts itself with the sibling tools.

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 only implied: 'from its model name' suggests calling it once the traveller's device is known. There is no statement of when to prefer it over coverage_check or quote_trip, no prerequisites, and no exclusions. Adequate but the agent must infer the routing decision.

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