MarkItDown is a Python library and CLI tool that converts a wide variety of file formats (PDF, DOCX, PPTX, XLSX, HTML, CSV, JSON, EPUB, Outlook MSG, images, audio, YouTube, RSS, IPYNB, ZIP, and more) into Markdown. Its primary production use is preparing documents for LLM ingestion, agent workflows, and text analysis pipelines. The architecture is a monorepo containing the core `markitdown` package, an OCR extension (`markitdown-ocr`) that uses LLM Vision for image text extraction, an MCP server (`markitdown-mcp`) exposing conversion as a tool for AI agents, and a sample plugin for third-party converters. The core library uses a plugin system based on `importlib.metadata.entry_points` to register converters, each implementing a `DocumentConverter` base class with `accepts()`/`convert()` methods and a priority-based dispatch. The main entry points are the `MarkItDown` class (Python API), the `markitdown` CLI, and the MCP server's `convert_to_markdown` tool. Data flows from local files, streams, HTTP responses, or URIs through converter selection (by MIME type, extension, or content inspection) to produce Markdown output. External dependencies include many optional format-specific libraries (pdfminer.six, python-docx, python-pptx, openpyxl, etc.), external binaries (exiftool, ffmpeg), cloud APIs (Azure Document Intelligence, Azure Content Understanding), and an OpenAI-compatible LLM client for image captioning and OCR.