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

Annotations are minimal (only a false readOnlyHint), so the description carries the full burden and does so well: it discloses the per-launch override that reverts on relaunch, the session-reuse vs direct-launch branching and that the tool reports which path it used, the runtime NSLocalizedString requirement, and the legacy cold-launch caching workaround.

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?

Front-loaded with the core purpose and benefit before the caveats, and each sentence carries actionable information. It is slightly long with a parenthetical example and two related caveat sentences, but nothing is wasted.

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 launch-with-override tool with no output schema, the description covers purpose, scope, side effects, session behavior and failure modes (legacy locale caching) including its output claim of reporting which launch path was used. An agent has everything needed to call it correctly.

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%, so udid, bundleId, language and locale are already documented with examples and the default locale derivation. The description alludes to the language/locale relationship but adds no syntax or format detail beyond what the schema provides, so the baseline 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?

States a specific verb (launch), resource (iOS app) and a precise qualifier (forced into a specific language/locale without changing device settings). This clearly distinguishes it from the plain ios_launch_app and the system-wide ios_set_device_language siblings.

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 a clear use case (QA testing app localization, e.g. Spanish without flipping the device) and contrasts against changing system settings, plus a remediation note (kill via ios_kill_app and re-call). It stops short of naming the specific alternative sibling tools an agent should pick between, but the when-to-use context is unambiguous.

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