What it does Prompt Optimizer is a client-side web app (plus desktop, Chrome extension, and Docker) that takes rough prompts and iteratively rewrites them for better results. It supports both system and user prompt optimization, then lets you evaluate outputs side-by-side before saving the winners as versioned “prompt assets.”

The interesting bit The project doesn’t just expand prompts with more adjectives. The demos show it restructuring a vague role prompt into a structured critique framework, and turning a one-line image idea into a spatially-directed composition. It also handles variable substitution for reusable templates and multi-turn conversation testing — treating prompts more like testable code than magic spells.

Key highlights

• Pure frontend: data stays in your browser, API calls go direct to providers
• Multi-model support: OpenAI, Gemini, DeepSeek, Grok, and several Chinese providers
• Image generation mode: T2I, I2I, multi-image, and style transfer via Gemini/Seedream/Grok
• “Smart Favorites” with version history, source binding, and full export/import
• MCP protocol support for Claude Desktop integration
• Desktop app avoids CORS issues and supports auto-updates

Caveats

• The README warns against pre-configuring API keys in VITE_* env vars on public deployments because they leak to the browser
• Chrome Web Store version may lag behind due to approval delays
• AGPL-3.0 license; commercial use requires compliance

Verdict Worth a look if you’re burning API tokens on poorly-structured prompts or need to share prompt templates across a team. Skip it if you already have a rigid prompt management system you’re happy with, or if you only ever chat with LLMs casually.