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

With no annotations provided, the description carries the full burden. It discloses the persistence and reboot survival, the implementation via reflection into ActivityManagerNative.updateConfiguration, and all known platform-specific failure modes. This is exemplary transparency for a mutation tool.

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 well-organized sentences: purpose first, then alternative, then caveats. No filler, every sentence adds actionable information, and the most critical scope is front-loaded.

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 system-level mutation tool with no annotations or output schema, this description covers all necessary context: persistence, scope, alternatives, and all known caveats. An agent has everything needed to decide when and how to invoke it, and what to expect.

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 the description need not repeat parameter details. It does not add extra meaning beyond the schema, but the baseline of 3 is appropriate since the schema already fully documents all four parameters. The description does not hurt or enhance parameter understanding.

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?

Description explicitly states the verb 'Change', the resource 'Android device's system language and locale', and adds key attributes: persistent, affects every app, survives reboot. It also distinguishes itself from the sibling device_launch_app_in_language, making its scope unambiguous.

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?

Provides explicit when-to-use guidance: 'For per-app testing without changing the whole device, prefer device_launch_app_in_language'. Also lists caveats (Samsung/MIUI re-applying locale, Android 14 hidden_api_policy, MDM refusal) that inform when this tool may fail, giving an agent decision criteria.

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