rn-device-mcp

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Screenshot the Android device

android_screenshot

Read-only

Captures an Android device or emulator screen and returns it as an image, so coding assistants can inspect UI state, verify changes, and debug visual issues.

Instructions

Captures the device screen and returns it as an image.

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": "android_screenshot"
  }
}

Input Schema

Name	Required	Description	Default
`serial`	No	adb serial (from android_devices). Default: the only online device.
`maxDimension`	No	Downscale so the longest side is at most this many px (default 900; 0 keeps the original size).

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0Nov 4, 2026

TDQS

A3.6/5.0

Behavior3/5

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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered and the description adds the return type (an image). It does not disclose the default downscaling behavior or the device-selection fallback, both of which are behavioral details an agent would want.

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?

A single sentence with zero filler, front-loading the action and stating the return type. Nothing is redundant and nothing needs to be moved forward.

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?

The tool is simple: two optional parameters fully covered by the schema, read-only annotations, and no output schema, so the description needn't explain return values. The only mild gap is that it never mentions the device-selection prerequisite or the size-downscaling side effect, though both live in the schema.

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

Parameters3/5

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

Schema description coverage is 100%, so both parameters (serial with its default-to-only-online-device behavior, and maxDimension with its 900px default and 0 sentinel) are already fully documented. The description adds nothing beyond the schema, which is the expected baseline here.

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

Purpose4/5

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

States a specific verb and resource ("Captures the device screen") plus the return form ("returns it as an image"). It is clearly distinct from ios_screenshot only by way of the tool name and the Android sibling set, not by anything in the description itself.

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

Usage Guidelines3/5

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

Usage is only implied: an agent infers a screenshot is for visual inspection of the emulator/device state. There is no explicit when-to-use, no mention of the ios_screenshot alternative, and no note about calling android_devices first to obtain a serial.

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