Langfa.st

Langfa.st is a lightweight AI prompt playground designed for rapid testing, refinement, and comparison of prompts across 50+ models including GPT-4, Claude, and Mistral. It supports Jinja2 templates, variables, and instant execution — all without sign-up or API keys. Ideal for prompt engineers, AI teams, and developers who need a fast, hassle-free environment to test and optimize prompt behavior in real time.