FableCut: An MCP Server for a Browser Video Editor
FastPresence9799 · reddit · 2026-07-17
FableCut is a browser-based video editor that also provides an implementation as an MCP server and has been added to the official registry. The author emphasizes that the focus of this post is not "video editing" itself, but how it functions as an agent-callable editing backend.
Key Features
- Zero dependencies: A browser-based NLE where the entire state is saved in a single JSON document
- Hand-written stdio JSON-RPC MCP server: Built without relying on the MCP SDK
- Provides 7 tools, including:
- fablecutstatus: Automatically launches the editor
- fablecutdocs: Exposes the agent manual on demand
- fablecutgetproject / fablecutsetproject
- fablecutpatchproject: Op-based localized patching
- fablecutimportmedia
- fablecutanalyzereference: Analyzes reference videos to extract shot segmentation, beats, BPM, loudness curves, per-shot energy, drop points, and audio tracks
Design Highlights
- Conflict-safe concurrent editing: The UI, MCP tools, and direct file writes all share a revision count. If a manual modification occurs, subsequent agent writes will be rejected with a conflict error
- Token efficiency is a core constraint: patchproject and compact read modes are designed to prevent repeatedly transmitting the full JSON for large projects
- Supports three methods (MCP, REST, and direct file writes) to access the same state
The author also seeks community input on experiences with op-based patching for nested/array states.
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