vphone-mcp

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

With no annotations provided, the description carries full burden. It discloses that the action is a 'tap' (implying a touch interaction), specifies coordinate system details (pixels matching 1290x2796 dimensions), and mentions dependency on screenshot() for target identification. It doesn't mention side effects like app responses or timing, but covers core behavioral context adequately.

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?

Perfectly structured: purpose statement first, then coordinate system context, usage guideline, and parameter details. Every sentence earns its place with zero waste. The description is appropriately sized for a simple 2-parameter tool.

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?

Given the tool's simplicity (2 parameters, no annotations, but has output schema), the description is complete. It explains what the tool does, how to use it, coordinate system, and parameter meanings. With output schema existing, return values needn't be explained in the description.

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 fully compensate. It provides complete parameter semantics: defines x as 'Horizontal pixel coordinate (0=left, 1290=right)' and y as 'Vertical pixel coordinate (0=top, 2796=bottom)', including coordinate system orientation and valid ranges. This adds essential meaning beyond the bare schema.

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 the specific action ('Tap at specific pixel coordinates') and resource ('on the screen'), distinguishing it from siblings like swipe, scroll, or button presses. It precisely defines the tool's function without ambiguity.

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?

Explicit guidance is provided: 'Use screenshot() first to identify the target position.' This tells the agent when to use this tool (after screenshot) and implies an alternative approach for coordinate identification. It also distinguishes from other interaction tools by focusing on precise coordinate-based tapping.

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