Marker is a high-accuracy document-to-markdown converter that transforms PDFs, images, DOCX, PPTX, XLSX, HTML, and EPUB files into clean markdown, JSON, HTML, or chunked output. It uses a pipeline architecture: a Provider extracts raw text and layout from the input, Builders (layout, line, OCR) construct a structured document model, Processors apply domain-specific transformations (table reconstruction, equation extraction, footnote handling, LLM-based correction), and Renderers produce the final output format. The system is driven by the Surya VLM for layout analysis and OCR, with an optional LLM enhancement layer (Gemini, Claude, OpenAI, etc.) for complex tasks like table merging, inline math, and image descriptions. Key entry points include CLI tools (`marker`, `marker_single`), a FastAPI server (`marker_server`), a Streamlit GUI, and a Python API (`PdfConverter`, `TableConverter`, `OCRConverter`). External dependencies include surya-ocr, pdftext, pypdfium2, torch, transformers, and various LLM SDKs. The codebase is well-structured with a clear separation of concerns, extensive test coverage, and a benchmark suite (olmocr-bench) that validates quality scores (~76% overall balanced mode).