Prompt Mixer

What is Prompt Mixer?

Prompt Mixer is an open-source desktop application for prompt engineering. It lets users build, version, test, and compare prompt chains across multiple LLM providers. Built with Electron and TypeScript, it runs on macOS, Windows, and Linux. The Community Edition is MIT-licensed.

How It Works

The core concept is prompt chaining: sequences of prompts where the output of one step feeds into the next. Chains can be combined with datasets for batch testing. The app uses a connector architecture, where each LLM provider integration is a separate plugin. Official connectors exist for OpenAI, Anthropic, Google Gemini, DeepSeek, Perplexity, Cohere, AI21, Amazon Bedrock, Azure OpenAI, OpenRouter, Ollama, and DeepInfra. Image generation connectors (DALL-E, Stable Diffusion) are also available.

Key Features

Built-in version control tracks every change to prompts and chains, enabling rollback and experimentation. Multi-model comparison lets you run the same prompt against different models side by side. Output validation supports regex matching, semantic similarity, JSON schema validation, external API endpoints, and custom JavaScript or Python evaluation code. A workflow builder provides a form-based interface for constructing analysis chains.

Pricing

The Community Edition on GitHub is free and MIT-licensed. A paid tier at $29/month appears to exist for commercial or team use, though the details are not prominently documented. All core prompt engineering functions are available in the free version.

Who Should Use Prompt Mixer?

Prompt Mixer is suited for developers and prompt engineers who prefer a local desktop tool over SaaS platforms for iterating on prompts. The connector system provides flexibility, but requires more setup than hosted alternatives. The project is pre-1.0 (version 0.2.9) with a small community (84 GitHub stars), so expect less polish than more established tools like promptfoo.