cd /news/developer-tools/show-hn-promptlab-local-first-chrome… · home topics developer-tools article
[ARTICLE · art-117525] src=github.com ↗ pub= topic=developer-tools verified=true sentiment=· neutral

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

PromptLab, a local-first Chrome extension for testing LLM prompts, was released on Hacker News. The Manifest V3 side panel, built with React, TypeScript, and Vite, stores up to 20 prompt fixtures entirely in chrome.storage.local with no analytics, remote APIs, or cloud storage, ensuring data never leaves the machine.

read1 min views1 publishedSep 1, 2026
Show HN: PromptLab – Local-first Chrome sidepanel for LLM prompt testing
Image: Michielbdejong (auto-discovered)

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 buildchrome.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

(orlocalStorage

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

  • Permissions: storage

,activeTab

, andsidePanel

(needed to host the dashboard)

── more in #developer-tools 4 stories · sorted by recency
── more on @promptlab 3 stories trending now
sponsored brought to you by zahid.host 4,200+ EU-deployed projects
reading about agents? ship yours in a single git push.

Run your AI side-project on zahid.host

EU-based hosting, git-push deploys, automatic HTTPS, no cold starts. Free tier with a custom domain — perfect for shipping the agent you just read about.

$git push zahid main
Live at https://your-agent.zahid.host
Get free account → Pricing
from €0/mo · no card required
LIVE [news/show-hn-promptlab-lo…] indexed:0 read:1min 2026-09-01 ·