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android-mcp

android-mcp

by mii-shell
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TypeScript
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screenshot

Capture the device screen as an image when UI tree data lacks visual details; returned pixel coordinates match other tools, and an optional region crop helps read small text.

Instructions

Take a screenshot (costs far more tokens than get_ui; use it for visuals the tree lacks). Its pixel coordinates are the screen coordinates every other tool uses. With region, returns a sharper crop for reading small text; a crop's pixels are NOT screen coordinates.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "screenshot"
  }
}

Input Schema

NameRequiredDescriptionDefault
regionNoScreen-coordinate rectangle to zoom into
serialNoadb serial; optional when exactly one device is connected

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4.6/5.0
Behavior4/5

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

With no annotations, the description carries the disclosure burden and does well: it warns about token cost relative to get_ui and flags the critical coordinate-frame trap that a crop's pixels are NOT screen coordinates. It does not mention multi-device behavior or failure modes, but the important behavioral caveats are present.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, front-loaded with the action and cost signal, then the coordinate rule, then the region nuance. Nothing is redundant and every clause carries decision-relevant information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

There is no output schema, and the description adequately implies an image result plus the coordinate frame of the returned pixels, which is the main ambiguity for a screenshot tool. Minor gaps remain around serial/device selection and resolution behavior, but they are documented in the schema.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so baseline would be 3, but the description adds real meaning the schema lacks: region produces a sharper crop rather than a resized image, and the returned crop's pixel frame differs from screen coordinates. That resolves the most likely misuse of the region parameter.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

Starts with a specific verb+resource ("Take a screenshot") and immediately distinguishes itself from the sibling get_ui by stating the cost/benefit tradeoff. An agent can pick between the two without opening either schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicit when-to-use guidance: cheaper get_ui is the default, screenshot is for "visuals the tree lacks", and region is for "reading small text". The alternative and the conditions that select it are both named.

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

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