In the vault folder you chose, as ordinary Markdown files. Open the folder in Finder and you'll see them. Header also keeps a hidden .header folder in the vault for note history, privacy receipts, starred notes and sidebar state, and a cache of thumbnails.

The search index lives outside the vault, in Header's own Application Support folder. It's derived data: if it ever looks wrong, Rebuild search index in Settings → Privacy & Data makes a fresh one from your files.

No account required. Header has no hosted note service, so there's nothing to sign up for. Signing in to GitHub is optional and only matters if you want to back up a vault to GitHub with Git in the download version.

Writing, saving, search, Graph, Lenses and indexing stay on your Mac. The main things that go out, each only when you use it:

• Saving a link or loading a remote image: the address goes to that website.
• Looking up a source (DOI, arXiv and the like): the identifier goes to the lookup service.
• Cloud AI: only after you turn it on and add a key. Header shows a preview of what will be sent unless you switch that off. See Setting up AI.
• Web search for Ask Header: only when you turn it on and use it.
• Git sync (download version): your vault's history goes to the remote you added.
• Research discovery: only your typed query goes to the search services you turned on.
• Update checks: download version only, once a day while Check for updates automatically is on, or when you choose Check for Updates…. Nothing from your notes is sent.

Approved cloud sends and research lookups are listed in Privacy Receipts (Settings → Privacy & Data → View Receipts…). More in Trust, safety & privacy.

Header adds no charge on top of AI. You also don't need AI at all: notes, links, search, tasks, exports and Minutes work without it.

When you want AI, you have three routes. Apple Intelligence runs on your Mac where macOS offers it (Apple silicon with macOS 26 or later, with Apple Intelligence turned on). Ollama runs a model you install yourself, with no key. Or you add your own key from OpenAI, Anthropic or Mistral, and that provider bills you for what you use. Settings → Privacy & Data shows how many billed cloud AI calls you've made this month, counted on your Mac.

Yes. Choose File → Bring Notes into Header…, pick Obsidian or Markdown folder, then decide how Header should use it:

• Open as Vault: the files stay where they are and the import doesn't rewrite the folder.
• Copy into Current Vault: copies land under Imported/ and the originals stay untouched.

Then set Markdown Compatibility to Obsidian-Friendly for that vault (Settings → Editor → Advanced editor options…). It turns on wiki links, aliases, callouts, tags, frontmatter, Mermaid and math. The full walkthrough is in Bring your notes in.

Keep the vault in a folder a sync service manages on your Mac, such as iCloud Drive, Dropbox or OneDrive. Header reads and writes the Markdown; the service moves it between machines. Two ways Header helps when edits collide:

• If a note changes on disk while you have unsaved edits, a Changed outside Header bar offers Review Changes, Keep Mine, Use Disk and Save Both. Header won't overwrite the other version on its own.
• Open Sync Recovery… (Settings → Sync & Backup) lists conflict copies. For a note edited on two devices you can Keep Mine, Keep Other or Apply Merge. Scan for Possible Duplicates looks for OneDrive-style duplicates and changes nothing by itself.

In the download version you can also sync through Git. See Sync & backup.

Your notes are plain files in one folder, so any backup that includes that folder, such as Time Machine, includes your notes. With history sync on, it also includes the .header folder that holds their history.

For an off-device copy with versions, the download version has File → Back Up Vault with Git…. Add a remote (for example a private GitHub repository) and Header pushes the vault's history there. A private GitHub repository isn't end-to-end encrypted; locked notes stay encrypted.

With Sync note history across your devices on (the default, in Settings → Sync & Backup), history is stored in the vault under .header/history/, so it travels with the vault to your other Macs. Turn it off and history stays only on this Mac. The text of locked notes is never written to history.

To look back, open the note's History in the Note Inspector. Each version can be shown as Rich, Markdown or Changes, and Restore brings it back. See The Note Inspector & history.

Rich mode draws your Markdown with formatting; the file itself stays plain Markdown. Switch to Source mode to see the text exactly as it's stored. The Markdown Compatibility setting never rewrites existing files, and the Rich content settings (table density, callouts, completed tasks and so on) only change how Rich mode draws the note.

If you ever spot a change in a part of a note you didn't edit, open History, choose Changes to see the difference, Restore the earlier version if you need to, and tell the team with Report Issue....

Header needs macOS 14.4 or later. The download from headernotes.com is notarized by Apple, so macOS should open it after a one-time confirmation. If macOS says the app is damaged or can't be checked, delete it, download it again from headernotes.com and drag the new copy to Applications. More in Install, update & first launch.

If Header is running but you can't see its window, closing the window only hid it. Choose Window → Show Main Window, or press ⌃⌥H from any app.