Prompt Tester provides an MCP server designed to empower agents with the ability to rigorously test and compare language model prompts across various providers like OpenAI and Anthropic. It allows for easy configuration of system prompts, user prompts, and other parameters, enabling developers to optimize LLM interactions. The server supports both stdio and SSE transport and includes tools for comparing prompts side-by-side, managing multi-turn conversations, and discovering available LLM providers and models. This simplifies the process of finding the most effective phrasing, comparing different models, and maintaining context in stateful interactions.