open_app

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

The description discloses that unknown/not-installed apps yield a structured APP_NOT_INSTALLED error with a suggestion to use the exact package name. This adds value beyond the input schema, which only describes parameters. With no annotations, it covers an important failure mode, though it stops short of other behavioral details such as foregrounding or permissions.

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 purpose, followed by a concrete error-handling detail. Every word 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?

Despite having 3 parameters and an output schema, the description covers the main action and a key error case. However, it does not mention session_id or differentiate from open_settings, leaving some ambiguity in tool selection. Overall, the description is sufficient but not comprehensive.

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 already describes app_name and device; the description's 'friendly name or package name' paraphrases app_name's examples. session_id remains undocumented at 67% coverage, and the description does not clarify it. The added semantic value over the schema is minimal.

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 opens with 'Launch an installed app by friendly name or package name,' which clearly states the action and resource. It distinguishes from sibling open_settings by implying a general app launcher, though it doesn't explicitly name that sibling.

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 implies the usage scenario: to launch an installed app. However, it provides no explicit when-not-to-use guidance and does not mention alternatives like open_settings. The error hint is about failure recovery, not tool selection.

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