Put the place you write notes and the place your AI agent reads and writes into a single folder. That is the idea behind Hubble.md, a free notepad app that has been drawing attention among developers. What gets saved is not a proprietary format but ordinary Markdown files. Hand the same folder to a coding agent such as Claude Code, and the agent edits your notes directly while the app reflects the result. It is MIT licensed, and the full source code is public.
What Gets Saved Is Not a Proprietary Format, Just .md Files
Hubble.md works on a per-folder basis. Launch it, register any folder, and the .md files inside show up in the side panel. If you already have a pile of Markdown notes, opening that folder is the whole migration.
That "just files" property is really the core design decision. Note apps that lock content inside their own database need an API or a plugin before an outside tool can touch anything. By making the file system itself the shared interface, Hubble.md removes that layer entirely.
The Writing Experience Is Modeled on Notion and Apple Notes
Being file-oriented does not make it a bare text editor. Typing / opens a command menu for headings, bullet lists, quotes and more, and typing Markdown syntax such as ## or - converts to the matching format inline. The goal is a feel that people coming from Notion or Apple Notes can pick up without friction.
Notes can also carry properties. Adding attributes such as category, status or tags through Add property writes them into the front matter at the top of the Markdown file. For a human these are organizational labels; for an AI agent they are the clue to what kind of note this is and what state it is in.
Calling the Agent Happens Inside the App
Choosing Chat about this note from the menu at the top right of a note opens a shell at the bottom of the editor and starts Claude Code with the current note already loaded. There is no jumping between an editor and a terminal. Claude Code launches by default, and you can switch to another agent in the settings screen.
When the agent rewrites a file, Hubble.md picks up the change through live reload. The loop of the AI drafting and the human correcting runs inside one window. Asking it to plan an itinerary and append the result to the note works exactly like that.
It Can Also Turn a Pile of Notes Into an HTML App
Where Hubble.md steps beyond Markdown is its HTML app feature. Install the officially distributed skills, then tell a coding agent something like "turn this into a map," and an HTML file is generated. Open that file inside the app and it runs as an interactive app rather than a static image or preview.
The examples given are tables, bookshelves and maps. In short, anything you can express in HTML can become a view, which breaks the usual assumption that adding a new display format means waiting for the app itself to support it.
Parts of It Are Still Under Development
The builds available now are on the 0.1 line, so this is not a finished product on sale. The official repository states plainly that the browser version and the file sync engine are still works in progress.
The supported environment deserves a look too. The README notes that macOS is what the developer has verified, that Windows and Linux are untested, and that contributions toward supporting them are welcome. Before adopting it, check whether a build exists for your platform.
The licensing side, on the other hand, is clear. MIT means you are free to fork it for personal use or use it at work. The editor core is built on Tiptap, and the repository is organized as a pnpm workspace, which makes it approachable for developers who want to modify it.
Summary
Hubble.md keeps notes stored as plain Markdown and, by doing so, reduces the machinery needed to work with an AI agent to a minimum. The writing side, from slash commands to front matter properties, stays close to existing note apps, while HTML app generation adds something existing apps do not offer. The 0.1 versioning and the macOS-centric support are real constraints, but for anyone who wants to rebuild their note-taking around handing work to an AI, the direction is worth trying.
