glTF (GL Transmission Format) is an open standard file format for 3D scenes and models. The repository at https://github.com/khronosgroup/gltf serves as the central hub for the specification's development, tooling, and validation efforts. It's maintained by the Khronos Group, a consortium focused on open, royalty-free interoperability standards for 3D graphics, vision, and parallel computing. Essentially, glTF aims to be the "JPEG of 3D," providing a compact, efficient, and widely supported format for transmitting and loading 3D content.

The core goal of glTF is to address the challenges of delivering 3D content on the web and in applications. Traditional 3D formats like OBJ or FBX are often verbose, requiring significant parsing and processing time. glTF, in contrast, is designed for runtime efficiency. It achieves this through a JSON-based structure that describes the scene's geometry, materials, textures, and animations. Crucially, it supports PBR (Physically Based Rendering) materials, enabling realistic and consistent rendering across different platforms. The format also allows for embedding or referencing external resources like textures and binary data, offering flexibility in content delivery.

The repository contains several key components. The `specification` directory holds the official glTF specification documents, detailing the format's structure, data types, and extensions. These documents are available in various formats, including HTML and Markdown, making them accessible to developers. The `validator` directory houses the glTF validator, a crucial tool for ensuring that glTF files conform to the specification. This validator is available as a command-line tool and as a web-based service, allowing developers to quickly identify and fix errors in their models. It's vital for interoperability, as it guarantees that a glTF file will be correctly interpreted by different rendering engines.

Beyond the core specification and validator, the repository includes numerous examples, tools, and extensions. The `examples` directory provides sample glTF files demonstrating various features and techniques. The `tools` directory contains utilities for converting between glTF and other 3D formats, as well as tools for optimizing glTF files. Perhaps most importantly, the repository actively supports glTF extensions. These extensions allow developers to add functionality beyond the core specification, such as support for specific rendering techniques or custom data attributes. The extension mechanism ensures that glTF can evolve and adapt to new technologies without breaking backward compatibility.

The glTF project is actively maintained and widely adopted. It's supported by major 3D engines and platforms, including Three.js, Babylon.js, Unity, Unreal Engine, and many others. This broad support makes glTF an ideal choice for delivering 3D content in web applications, games, augmented reality (AR), and virtual reality (VR) experiences. The repository's issue tracker and discussion forums are active communities where developers can ask questions, report bugs, and contribute to the project's ongoing development, solidifying glTF's position as a leading 3D format for the modern web and beyond.