Prompt files are structured, serialized formats designed to manage prompts in AI systems, especially those powered by large language models (LLMs), making them easier to integrate into version-controlled development workflows. Inspired by MDX, these files utilize YAML headers for configuration and JSX-like syntax for defining chat templates, multi-modal interactions, and tool integrations, allowing technical teams to treat prompts as first-class artifacts. This format supports multi-modal interactions through XML-like tags, enabling the combination of text and images while adhering to strict schema validation. Additionally, prompt files allow developers to specify tools within the YAML header that an AI model can use during interactions, enhancing consistency, collaboration, and control in AI development workflows. Humanloop provides solutions for implementing production-grade prompt management, supporting prompt files, multi-modal interactions, and tool-augmented workflows to optimize LLM performance across complex applications.