Open the app

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

With no annotations, the description carries the behavioral disclosure. It explains the Expo/React Native dev-client path (Metro on port 8081 and the app's registered scheme), which is genuinely helpful. However, it does not state failure behavior, such as what happens when no simulator is booted, no Metro server is listening, or the app is not an Expo dev client.

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 just two sentences. The core action is front-loaded, and the conditional Expo behavior is stated in a compact second sentence with no wasted words, making it easy to scan.

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 tool with no annotations and no output schema, the description covers the main call scenario and the important dev-client exception. It does not mention failure cases, which is a moderate gap, but the essential context for invoking the tool is present.

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 input schema is empty, so there are zero parameters to document and schema coverage is trivially complete. With no parameters, the description correctly adds no parameter-specific semantics, and the baseline of 4 applies.

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 what the tool does: opens the app on the booted simulator. It also distinguishes itself from the sibling tool launch_app by calling out the Expo/React Native dev-client case, so an agent can separate roles without opening the schema.

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 says 'For a regular app, prefer launch_app,' giving the agent a direct routing rule. It also implies the favorable scenario for open_app — Expo/React Native dev clients — and where the tool fits relative to launch_app.

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