Promptmetheus

Promptmetheus is a browser-based IDE for composing, testing, and optimizing prompts for large language models. Prompts are built from modular blocks — context, task, instructions, samples, and primer — that can be independently edited and recombined, which makes it easier to isolate what part of a prompt is driving a given output. The tool connects to roughly 15 LLM providers and 150+ models, including OpenAI, Anthropic, Google, Mistral, Cohere, Perplexity, xAI, DeepSeek, and Groq, so the same prompt can be run and compared across models side by side. Testing features include custom evaluators for automatically validating completions, dataset-based testing across many inputs at once, completion ratings, cost estimation per run, and full version history for traceability. Teams can collaborate in shared workspaces in real time, and results can be exported as .txt, .csv, .xlsx, or .json. It integrates with LangChain and exposes an API, though the site does not describe the API's scope in detail. Promptmetheus is built for prompt engineers, AI developers, and teams shipping LLM-powered products who need a repeatable way to compare model behavior. Pricing starts with a free single-user Playground restricted to OpenAI models, then $29/month for full model access, and $99/month for a 3-seat team plan. One limitation: the free tier is OpenAI-only, so evaluating other providers requires a paid plan.