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

With no annotations, the description carries the burden of behavioral disclosure. It adds the crucial asymmetry about region-qualified current language vs base codes for setting, and mentions the error string. It implies read-only via 'list' but doesn't explicitly state no side effects; still, it provides substantial behavioral context beyond the bare function.

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?

The description is moderately long but every sentence adds value: purpose, usage warning, and an important asymmetry detail. It is front-loaded with the core functionality and uses clear phrasing, though slightly verbose. Could be tightened but remains efficient.

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 simple read-only tool with one parameter and no output schema, the description conveys what will be returned (languages, locales, current language) and the critical caveat about setting. Even without an output schema, the agent knows what to expect. Nothing essential is missing.

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?

There is only a single udid parameter, and the schema description already covers it fully (100% coverage). The description adds no further meaning about the udid itself, so the baseline of 3 is appropriate.

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 explicitly states it lists the languages/locales the device accepts plus the current setting, which is a specific verb and resource. It clearly distinguishes from the sibling ios_set_device_language by being the read-only counterpart.

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?

It tells the agent to read this before ios_set_device_language to avoid guessing a code, explaining that unsupported values are rejected with a bare 'SetProhibited' error. This explicitly gives the when-to-use and why, outperforming many descriptions.

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