Prompt Optimizer is an open-source tool that helps you write better prompts and get better results from AI models. You paste in a rough prompt, and it rewrites, structures, and refines it using proven prompt-engineering patterns, then lets you test and compare versions side by side. The project has collected over 38,000 stars on GitHub and was actively maintained in October 2026.
Good prompts are a skill, and Prompt Optimizer turns that skill into a repeatable workflow. It supports optimizing prompts for chat models as well as image-generation prompts, offers templates for common tasks, and can evaluate outputs so you can see whether a rewrite actually improved results. It runs as a web app, a desktop app, and a Chrome extension, and it can also be deployed as an MCP server so other AI tools can call it. You bring your own model API keys, which keeps your data under your control.
Prompt Optimizer is free and open source. You can use the public web version at no cost or self-host your own instance; the only expense is whatever you pay for the model API keys you plug into it.
Prompt Optimizer is for anyone who works with LLMs daily: prompt engineers, content creators, developers building AI features, and teams who want consistent, higher-quality model outputs. If you often iterate on the same prompts by trial and error, this tool systematizes the process.