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Screen Vision MCP Server

Screen Vision MCP Server

by avicuna
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
Local

capture_region

Captures a specific rectangular area of the screen defined by position and size, returning the frame data.

Instructions

Capture a specific screen region.

Args: x: Left coordinate of the region y: Top coordinate of the region width: Width of the region height: Height of the region scale: Scale factor for resizing (default: 1.0)

Returns: JSON string with captured frame data or error

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "x": "<x>",
      "y": "<y>",
      "width": "<width>",
      "height": "<height>"
    },
    "name": "capture_region"
  }
}

Input Schema

NameRequiredDescriptionDefault
xYes
yYes
scaleNo
widthYes
heightYes

Output Schema

NameRequiredDescriptionDefault
resultYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.3.4

TDQS

B3.4/5.0
Behavior2/5

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

With no annotations provided, the description fails to disclose behavioral traits such as whether the tool is read-only, requires permissions, or has side effects. Only the return format is mentioned, which is insufficient.

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?

The description is extremely concise: one sentence for the purpose followed by a structured list of arguments and return type. No redundant information.

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

Completeness2/5

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

Despite having an output schema, the description does not explain the contents of the captured frame data (e.g., format, encoding). Additionally, context about coordinate origins, bounds checking, and error scenarios is missing.

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?

The schema has 0% description coverage, so the description's Args section is essential. It provides clear, albeit minimal, meaning for each parameter (e.g., 'Left coordinate', 'Width of the region'). This compensates for the schema gap.

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?

The description clearly states the tool captures a specific screen region, which is a distinct action from sibling tools that capture full screen, window, or camera. The verb 'capture' and resource 'screen region' are specific.

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

Usage Guidelines2/5

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

No guidance is provided on when to use this tool versus alternatives like capture_screen or capture_window. The description does not mention prerequisites, coordinate system origins, or error handling context.

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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