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

Annotations already mark read-only, idempotent, non-destructive, and openWorldHint false. The description adds context beyond annotations: the result is against a 'manufacturer-sourced' catalog, 'exact' model matching, and the meaning of unknown results ('never means incompatible'). This gives the agent important interpretive nuance not present in structured hints.

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?

Three sentences with no filler: purpose, usage context, caveat, and exclusions. The most important information (what it checks) is front-loaded, and every clause earns its place without redundancy.

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 the 7-parameter schema and existence of an output schema, the description covers the essential operational aspects: purpose, usage context, and unknown-result interpretation. It does not enumerate every parameter, but the alluded factors are the ones that matter for device-readiness, and the output schema handles return-value details.

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 description coverage is only 29%, so the description partially compensates by referencing 'regional variants', 'carrier locks', 'EID', and 'Add eSIM settings', which map to region, carrierUnlocked, eidPresent, and addEsimSettingPresent. However, it does not clarify locale or manufacturer parameters, leaving some semantic gaps for a low-coverage 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?

States a specific verb ('check'), resource ('eSIM compatibility catalog'), and the exact scope ('exact phone model'). Clarifies it is a lookup tool, and the final sentence explicitly excludes searching, comparing, recommending, pricing, or selling plans, distinguishing it from broader tools like build_travel_connectivity_guide.

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?

Directly instructs to use for 'device-readiness questions' and lists covered attributes (regional variants, carrier locks, EID, Add eSIM settings). Also provides a crucial interpretation rule ('Unknown never means incompatible') and states what the tool does not do, giving clear when-to-use and when-not-to-use guidance.

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