# Show HN: PromptLab – Local-first Chrome sidepanel for LLM prompt testing

> Source: <https://github.com/timgioh/PromptLab-Local-First-LLM-Prompt-Testing-in-Your-Browser>
> Published: 2026-09-01 08:33:50+00:00

Chrome extension (Manifest V3) for managing local prompt fixtures. Nothing leaves the machine: no analytics, no remote APIs, no cloud storage.

- React + TypeScript + Vite
- Tailwind CSS
`@crxjs/vite-plugin`

for the extension build`chrome.storage.local`

in the extension,`localStorage`

in the browser preview

```
npm install
npm run dev
```

Opens a local dashboard at `http://localhost:5173`

. Add, edit, and delete up to 20 prompt fixtures. **Run Eval** is a stub for tomorrow’s LLM wiring.

```
npm run build
```

Then in Chrome:

- Open
`chrome://extensions`

- Enable
**Developer mode** - Click
**Load unpacked** - Select the
`dist`

folder

Click the extension icon to open the side panel.

For live reload while developing the extension:

```
npm run dev:extension
```

Load the generated `dist`

folder as unpacked. Keep the Vite process running.

- Fixtures persist only in
`chrome.storage.local`

(or`localStorage`

in the web preview) - No telemetry, fonts-from-CDN, or outbound requests in this app
- Permissions:
`storage`

,`activeTab`

, and`sidePanel`

(needed to host the dashboard)