select_device

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

Annotations already declare readOnlyHint=true and openWorldHint=false, covering the safety profile. The description adds the session-scoped nature of the selection, which is useful. It does not disclose details such as whether the device must be connected first or how a previously active device is replaced, but given the annotations, this is acceptable.

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 a single, front-loaded sentence with no filler. It conveys the essential information concisely and efficiently.

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?

The tool is simple with one parameter, full schema coverage, and no output schema. The description plus schema sufficiently explain what it does and how to invoke it. It could mention that the active device will be used by subsequent commands, but 'active for this MCP session' covers this adequately.

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?

Input schema coverage is 100%, and the schema's parameter description is detailed (e.g., 'ADB serial such as emulator-5554, a USB serial, or host:port'). The tool description itself adds no parameter-related meaning, so 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?

The description uses a specific verb 'Select' and clearly identifies the resource (an emulator or physical device) and the scope ('active for this MCP session'). It distinguishes itself from sibling tools like list_devices, disconnect_device, and clear_active_device by focusing on making a device active.

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 provides clear context: use this tool to set the active device for the current session. It does not explicitly mention alternatives or when not to use it, but the purpose is unambiguous enough that an agent can infer when it applies.

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