Langfa.st

Langfa.st is a fast and minimal playground for testing and refining AI prompts. It supports over 50 large language models, including OpenAI, Anthropic, Mistral, Cohere, Google, and others — all available instantly without setup. Users can insert variables, use Jinja2 templating, and compare outputs across models without needing to sign up or provide API keys.

Pros of Langfa.st include: it works without login or API key, supports over 50 models out of the box, has built-in support for variables and Jinja2 templating, provides instant responses with no setup required, and features a clean and distraction-free user interface.

Cons of Langfa.st include the lack of custom API key support at this time and it may not be ideal for running complex multi-turn chats.

Langfa.st is particularly beneficial for AI teams and prompt engineers who need a clean, disposable space to experiment, debug, and iterate on AI prompts without the friction of complicated UIs or required credentials.

Yes, Langfa.st is free to use. Users only pay if they need more volume or access to power features.