An HTML file can be a standalone application

Hyperclay Local is a free, open-source desktop app that lets you create, modify, and use HTML files like local applications.

Screenshot of Hyperclay Local desktop app

(Hyperclay Local taskbar app)

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Local-first Apps

Anything that fits in a single HTML file and benefits from persistence:

A dev log, journal, or reading list
A time tracker or kanban board
A bookmarks page or recipe collection

Example malleable HTML file: development log

Example malleable HTML file: landing page

Dev-friendly workflow

Inspect everything. Right-click, View Source. The UI, the logic, the data — all in the markup.
Nothing phones home. No analytics, no telemetry, no accounts.
Works offline. The server and your files are on your machine. No internet required.
Backups on every save. The server keeps the previous version before overwriting.

A file that remembers

An HTML file can do a lot: lay out any UI, run JavaScript and hook into any browser API, respond to input.

The one thing it can't do is remember. Refresh and everything resets.

A malleable HTML file saves itself. It serializes its DOM and sends it to a local server. No database, no build pipeline, no dependencies.

One file is a complete application:

Email it
Commit it to git
Put it in Dropbox

What Hyperclay Local does

Browsers can open HTML files but can't write back to disk. Hyperclay Local provides that missing piece: a local Express.js server with a single endpoint:

POST /save/:name

Point it at a folder, click start. Your malleable HTML files save themselves to disk. That's the entire system.

Example malleable HTML file

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Notes</title>
  <script src="https://cdn.jsdelivr.net/npm/hyperclayjs@1.24.3/src/hyperclay.js?preset=minimal&features=autosave" type="module"></script>
</head>
<body>
  <h1 editmode:contenteditable>Notes</h1>
  <p editmode:contenteditable>Start typing here. Everything saves to disk automatically.</p>
</body>
</html>

Core features of HyperclayJS:

autosave
prevent leaving before saving
save keyboard shortcut
toast notification on save
edit mode

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Notes</title>
</head>
<body>
  <h1 contenteditable>Notes</h1>
  <p contenteditable>Start typing here. Everything saves to disk automatically.</p>
  <script>
    // This code handles saving the file whenever it changes
    const name = document.cookie.match(/currentResource=([^;]+)/)?.[1]
    const save = () => fetch('/save/' + name, {
      method: 'POST',
      headers: { 'Content-Type': 'text/html; charset=utf-8' },
      body: '<!DOCTYPE html>\n' + document.documentElement.outerHTML
    })
    document.addEventListener('input', save)
    new MutationObserver(save).observe(document, {
      childList: true, subtree: true, attributes: true, characterData: true
    })
  </script>
</body>
</html>

Extra features

Tailwind CSS on save. Add a stylesheet pointing to /tailwindcss/{yourFileName}.css. The server generates optimized Tailwind CSS on every save — only the utilities you actually use.
HyperclayJS. A modular JS toolkit for malleable HTML files. Autosave, edit mode, sortable lists, toast notifications, dialogs, and more. Load a preset or pick individual features.

Download

Free, no account required.

macOS (Apple Silicon): HyperclayLocal-1.13.3-arm64.dmg (100.7 MB)
macOS (Intel): HyperclayLocal-1.13.3.dmg (108.4 MB)
Windows: HyperclayLocal-Setup-1.13.3.exe (89.4 MB)
Linux: HyperclayLocal-1.13.3.AppImage (119.0 MB)

Source code: github.com/panphora/hyperclay-local

FAQ

How does the saving actually work?

Your HTML file includes a small script that serializes the page's DOM and sends it via POST /save/:name to the local server. The server validates it and writes it to disk, saving a backup of the previous version in a sites-versions/ folder. HyperclayJS handles this for you — the minimal preset includes saving, snapshots, and edit mode out of the box.

Linux says permission denied

AppImage files need to be marked as executable:

chmod +x HyperclayLocal-1.13.3.AppImage

Port 4321 is already in use

The server binds to port 4321 by default. If another process is using that port, the app will show an error. Kill the other process or wait for it to release the port.

The server won't start

Check that:

The folder you selected actually contains files
The folder path doesn't contain unusual special characters
Try selecting the folder again using the folder picker

How do I build from source?

Clone the repo and install dependencies:

git clone https://github.com/panphora/hyperclay-local.git
cd hyperclay-local
npm install

Development mode (live reload):

npm run dev

Build for your platform:

npm run build-mac      # macOS
npm run build-windows  # Windows
npm run build-linux    # Linux
npm run build-all      # All platforms

Is it safe to run?

The app uses several layers of protection:

Sandboxed renderer: Web content runs in an isolated Electron context, separate from the main process
IPC security: Communication between the renderer and main process uses secure Electron IPC channels
Path traversal protection: The server validates all file paths to prevent access outside the selected folder
Filename sanitization: Only allows alphanumeric characters, hyphens, and underscores in saved filenames
Content validation: The server validates file content before writing to disk

The app is open source. You can audit the full codebase at github.com/panphora/hyperclay-local.

Most software asks you to be beholden to someone else's ideas.

Hyperclay Local lets you own the full stack in one HTML file.