Connect to an Android device, set it as the session default, and retrieve its screen size and current app.
Connect to an Android device and remember it as the default for all subsequent tool calls in this session. Returns screen size and current app.
| Name | Required | Description | Default |
|---|---|---|---|
| serial | No |
| Name | Required | Description | Default |
|---|---|---|---|
| result | Yes |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden of behavioral disclosure. It does disclose the key side effect of remembering the device as default and the return type (screen size, current app). However, it does not explain behavior when serial is omitted, whether a previous default is replaced, or prerequisites like device visibility, so transparency is adequate but incomplete.
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, no filler. The core action and session-default behavior are front-loaded, followed by the return value. 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?
The tool is simple, and the description covers purpose, side effect, and returns, with an output schema present to describe the response structure. However, it omits guidance on the sole parameter (serial) and does not reference the sibling list_devices for discovering valid serials, leaving a meaningful gap for correct invocation.
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 0%, so the description must compensate by explaining the serial parameter. It does not mention serial at all. The parameter name is self-explanatory as a device identifier, but the optional/null semantics and behavior when omitted are left entirely to inference.
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 a specific verb ('Connect'), the resource ('Android device'), and the session-scoped side effect (becoming the default). It also states the return value, distinguishing it from siblings like list_devices and disconnect_device without needing to open 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 implies when to use the tool: before subsequent device-related calls in the session, since it establishes the default device. However, it does not explicitly mention alternatives (e.g., list_devices to discover serials) or specify when not to use it, leaving the guidance mainly implied.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.