PromptFast - Test agents on any model. No setup, no wait.

Hi, I’m Janos, the creator of PromptFast. Every developer building with AI faces the same bottleneck: testing a prompt requires running an entire pipeline. Change one word in your system prompt, spin up your environment, wait through multiple API calls, dig through logs, repeat. For multi-agent systems, this loop can take minutes - for hours of iteration work. PromptFast is a subscription-based SaaS playground for prompt engineers and AI developers. It provides an isolated, fast, multi-model environment to test, compare, and track prompts - without touching your application infrastructure. - Run a prompt against 13+ models across OpenAI, Anthropic, and Google simultaneously - See real-time token-by-token streaming responses - Track exact cost per run with model-specific pricing - Upload PDFs, CSVs, DOCX files as document context - Keep a full history of every experiment, reloadable in one click - Compare two models side-by-side with parallel execution