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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so safety is covered. The description adds real behavioral context beyond them: the answer is a lookup against a curated vendor list, the result is conditional on carrier-unlock status, and absence from the list is not proof of incompatibility.

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 core question, then the two caveats that matter. No filler, though the phrasing 'from the models eSIMpass documents' is slightly compressed and could be clearer about the lookup source.

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?

No output schema exists, so the description carries the return-value burden; 'whether a phone model supports eSIM' implies a yes/no verdict but the exact response shape is not spelled out. The critical ambiguities that would mislead an agent (carrier-unlock precondition, false negatives) are covered.

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 100% and the schema already gives worked examples ('iPhone 15 Pro', 'Galaxy S24', 'Pixel 8'), so the description has little to add. It only reinforces that the value is a phone model; baseline 3 is appropriate when the schema carries the parameter documentation.

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 resource and scope: whether a given phone model supports eSIM, plus the bounded data source (models eSIMpass documents for Apple, Samsung and Google). It is clearly distinct from siblings like get_plans or create_checkout_link, but it never explicitly says so, since differentiation is left to inference from the domain.

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?

Gives usable context for when the answer applies (device must be carrier-unlocked) and an important exclusion on how to read a negative result ('a model not in the list is not necessarily incompatible'). It does not name a sibling alternative, but no sibling performs this lookup, so the omission is minor.

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