List running apps

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

Annotations already declare the operation is read-only, idempotent, and non-destructive. The description adds meaningful behavioral context beyond annotations: it states no window or input is touched, and explains the multi-instance/window-ownership nuance that affects how an agent should use the results.

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 sentences, each earning its place: the first states purpose and output fields, the second gives operational guidance with a concrete use-before pattern, and the third reassures about read-only safety. No filler or repeated annotation material.

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 zero-parameter, read-only listing tool with no output schema, the description is complete: it enumerates the return fields, explains why the tool should be called first, and covers the instance-selection caveat. An agent has everything needed to call it correctly and interpret the result.

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 tool has zero parameters and schema coverage is trivially 100%, so there are no parameter details to explain. The description correctly focuses on the value of the tool's output rather than parameters.

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 ('List') and resource ('running applications') and enumerates the exact fields returned (bundle id, pid, window count, frontmost). It also explains the tool's role as the discovery entry point for sibling tools, distinguishing it from the rest.

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?

Explicitly instructs to call this tool first to learn the exact 'app' value accepted by get_app_state, screenshot, and activate_app. It also provides concrete guidance on choosing the right instance when multiple exist and only some own windows.

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