What is Folio?

Folio is a desktop app for reading and reviewing folders of Markdown: specs, architecture decision records (ADRs), design proposals, notes and Obsidian vaults. It's free and open source, for macOS, Windows and Linux.

Who it's for

Folio is for anyone who has to read documents closely rather than write them:

• Reviewers of specs and ADRs. A project's docs/ folder grows faster than anyone reads it. Folio shows which decisions are accepted, proposed or superseded, and lets you mark what needs another pass.
• People working with coding agents. Agents write specs, plans and decisions quickly. Folio is where you read them, mark them up and send your notes back. See Reviewing specs with a coding agent.
• Obsidian users who want a reader for their vault: wiki links, embeds and front matter work as they do in Obsidian.

What it does

• Lists every Markdown file in a folder and its sub-folders, with search across titles, headings and full text.
• Renders documents properly: tables, task lists, syntax-highlighted code, math and Mermaid diagrams.
• Reads each document's status and tags from its front matter or Status: line, and filters by them.
• Lets you highlight passages, write notes, give a verdict on a whole document and bookmark sections, then find every mark in one list.
• Copies your notes as Markdown for a coding agent, each with its file path and line.

What it doesn't do

• It never edits your files. Folio is a reader. Marks are kept in Folio's own folder, not in your documents. See the FAQ.
• It isn't an editor. Use your usual editor to change a document; File → Open in Editor (⌘E / Ctrl+E) opens it there, and Folio shows the change as you save.
• It isn't a sync or collaboration service. Marks stay on your computer.

Try it before installing

The live demo opens a sample repository of specs and ADRs in your browser, with nothing to install. Your highlights and notes stay in that browser.