# AfterPencil > AfterPencil is a floor plan editor that runs in the browser: walls, rooms, doors and windows, furniture, levels, structure, roofs, installations, terrain, finishes, 3D, quantity takeoff and technical drawings. Projects work without an account (saved in the browser) or in the cloud with one. An agent can read and edit the open project from JavaScript through `window.afterpencil`, with the same rules and undo history as a person using the editor. Without a browser, connect to the MCP server at `https://mcp.afterpencil.com/mcp`: it signs in with OAuth (the person chooses a workspace and whether you may edit) and offers the same commands as tools, plus a PNG of the floor plan to check your work. Use the JavaScript API when you can run code in the page (a browser agent, Claude in Chrome or Cowork, Playwright): it is faster and more reliable than clicking. Start with `afterpencil.summary()` to see what is there, edit with the commands, check each result's `ok`, and look at the result with `planImage()` and `capture3d()`. Every edit is one undo step; tell the person what you changed. ## Docs - [JavaScript API](/agents/js-api.md): every method of `window.afterpencil`, with arguments, results and examples. - [Plan model](/agents/model.md): units, coordinates, ids, levels, walls, wall types and rooms, openings with their products and size ranges, slabs, roofs, stairs, lot and fences, faces and finishes, and the main model operations for `apply()`. - [MCP server](/agents/mcp.md): how to connect, and its tools. - [REST API reference](https://api.afterpencil.com/openapi.json): OpenAPI 3.1 of what an agent or integration can reach (OAuth, projects). ## Optional - [Open the editor with a test plan](/editor?fixture=two-bedroom-house): any page accepts `?fixture=&view=2d|3d|split&select=`; `?wall=&face=left|right` opens the front view of a wall face.