Building an MCP Server for macOS Screen Control and Screenshots

Fazm Team··2 min read

Building an MCP Server for macOS Screen Control and Screenshots

When you are building a multi-agent workspace, every agent needs eyes and hands. The agent needs to see what is on screen and interact with UI elements. On macOS, this means screen capture and input control. An MCP server wraps these capabilities into a standard interface that any agent framework can consume.

What the MCP Server Exposes

The core tools are straightforward. A screenshot tool that captures the current screen or a specific window. A click tool that dispatches mouse events at coordinates or on accessibility elements. A type tool that sends keyboard input. A scroll tool for navigating content. And a read-screen tool that returns the accessibility tree of the frontmost application.

Each tool follows the MCP protocol - JSON-RPC over stdio. Any client that speaks MCP can use these tools without knowing anything about macOS internals.

Why MCP Instead of Direct API Calls

The value of wrapping screen control in MCP is interoperability. Your orchestrator can be Claude, GPT, a local model, or a custom agent framework. As long as it speaks MCP, it gets the same screen control capabilities. You swap the brain without rewiring the hands.

This also lets you run multiple agents simultaneously. One agent handles email while another manages your calendar. Both use the same MCP server for screen access, and the server handles coordination to prevent conflicts.

The Screenshot Pipeline

Raw screenshots are too large for most LLM context windows. The MCP server handles compression and cropping automatically. When an agent requests a screenshot, it gets a reasonably sized image focused on the relevant window - not a 5MB full-resolution capture of three monitors.

For text-heavy screens, the server also returns the accessibility tree alongside the screenshot. The agent can use the structured text for precise element identification and fall back to the screenshot for visual context when the accessibility tree is insufficient.

Fazm is an open source macOS AI agent. Open source on GitHub.

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