Every AI assistant reads markdown. Every AI assistant writes markdown. The context files that shape how agents behave, the specs that define what to build, the documentation that records why — all markdown. And yet the tools we use to work with these files haven’t caught up.
What’s missing is something that works like a browser for your files. Navigate folders, click into documents, hit back to return where you were. No project setup, no import wizard — just point it at a folder and start reading.
Markdown Library ML-42 is a native macOS app built for this workflow.
Works the way you already work
ML-42 opens your folders where they are. No import step, no database, no proprietary format. Add any folder as a project — a project repo, a docs directory, a notes folder — and ML-42 shows you its markdown files in a three-column layout: project tree on the left, content in the centre, inspector on the right.
Click a folder and you get document cards with titles, excerpts, and modification dates. Click a file and it renders with live preview — headings, code blocks, tables, front matter — all styled and navigable. Move your cursor into any block and the raw markdown appears for editing. Move away and it re-renders. Reading and writing are the same surface.
The more projects you add, the more useful it gets. Cmd+K searches across all of them at once — by filename and by content.
What it does
The features page has the full reference, but the highlights:
- Live preview editing — Obsidian-style cursor-aware rendering. No mode switching.
- Syntax highlighting for 15+ languages in fenced code blocks, with colours that adapt to light and dark mode.
- Table rendering — markdown tables as clean, aligned grids.
- Command palette — search across every project by name or content.
- Front matter — YAML metadata renders as a clean property list, not raw syntax.
- File watching — when an AI agent or another editor changes a file, ML-42 picks it up automatically.
- Back and forward navigation, favorites, table of contents, inline rename, and keyboard shortcuts for everything.
Why markdown matters now
Markdown’s role expanded quietly. It went from a formatting convenience for READMEs to the dominant medium for structured thought in AI-assisted work. The CLAUDE.md files that shape agent behaviour, the architecture docs that give AI context, the specs and briefs and decision records — these are the files that determine whether an AI interaction produces something useful or something generic.
Maintaining them well is one of the highest-leverage activities in any AI workflow. ML-42 is built to make that work feel less like editing config files and more like browsing a library.
We wrote a Markdown Primer that traces the format from John Gruber’s 2004 spec through CommonMark to its current role as the connective tissue of human-AI collaboration.
Nothing between you and your files
ML-42 is sandboxed. It reads and writes files on your local filesystem and does nothing else — no network requests, no telemetry, no accounts, no cloud sync. When you close the app, your files are exactly where you left them. When you open them in another tool, everything is there.
The documentation covers installation, the workflow, and a complete feature reference.
Beta
ML-42 is in active development and targeting macOS 26. Sign up on the product page to get notified when we launch.