openplayground is a web-based playground for testing large language models from OpenAI, Anthropic, Cohere, HuggingFace, Replicate, and other providers, as well as local models via llama.cpp. It provides a full UI with chat history, side-by-side model comparison, parameter tuning, and keyboard shortcuts. Users can detect and install models from their HuggingFace cache, and the tool works on mobile devices.