Langfa.st

About Langfa.st

LangFast is an online LLM playground designed for rapid prompt testing, evaluation, and iteration across multiple models, including GPT, Gemini, and Claude (though currently OpenAI/GPT is supported, with others potentially by request). Geared towards product teams and prompt engineers, it offers no-code prompt editing, side-by-side model comparison, automated evaluations, collaboration features, and more. Users bring their own API keys and can pay once for either 1-year or lifetime access.