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

With no annotations provided, the description carries the full burden of behavioral disclosure. It reveals an important asymmetry: the current language reads back region-qualified (e.g. 'en-CA') but only base codes can be set, and it warns about the error message. This is valuable behavioral context beyond a simple 'list' operation. It doesn't explicitly state that the operation is read-only, but 'List' implies it, and no side effects are expected. It could mention permissions or exact return format, but the disclosed behavior is sufficient for safe use.

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 concise, with three sentences that each add essential value: the main purpose, the usage guidance with a warning, and the critical asymmetry note. It is front-loaded with the primary function and no extraneous words. Every sentence earns its place.

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 tool with one parameter and no output schema, the description provides enough for an agent to call it correctly. It explains what the tool returns (languages, locales, current setting) and the key behavioral nuance. However, it doesn't explicitly outline the return structure (e.g., field names or format), which an agent might need to parse results. Since there's no output schema, a brief note on return format would make it fully complete, but the current description is adequate.

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?

The single parameter (udid) is fully documented in the schema with 'iOS device UDID' (100% schema coverage). The description adds no additional information about the parameter itself, which is acceptable given the schema's completeness. Per the rubric, baseline is 3 when schema coverage is high and description doesn't need to compensate.

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 clearly states the tool's purpose: 'List the languages and locales this iOS device accepts, plus what it is set to now.' It uses a specific verb (List) and resource, and distinguishes itself from the sibling ios_set_device_language by positioning this as the prerequisite read tool. An agent can immediately understand what it does and how it differs from the setter.

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 description explicitly instructs when to use this tool: 'Read this before ios_set_device_language rather than guessing a code.' It also explains the consequence of not doing so (an unsupported value is rejected with a bare SetProhibited). This is a clear usage guideline that routes the agent correctly and prevents errors.

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