What is a .gltf file?

What is in a .gltf file

A .gltf file is JSON. Open it in a text editor and you will find a structured description of a scene:

{

"asset": { "version": "2.0" }, "scenes": [{ "nodes": [0] }], "nodes": [{ "mesh": 0, "name": "bracket" }], "meshes": [{ "primitives": [{ "attributes": { "POSITION": 0 }, "indices": 1 }] }], "accessors": [ ... ], "bufferViews": [ ... ], "buffers": [{ "uri": "bracket.bin", "byteLength": 145200 }]

}

The JSON is the *structure*. The actual vertex coordinates live in a buffer, and that buffer is normally an external .bin file sitting next to the .gltf.

The missing .bin problem

This is the reason most people should use .glb instead.

A glTF export typically produces three or more files: the .gltf, a .bin, and one image per texture. Send someone only the .gltf and they receive a description of a model with no model in it. Upload only the .gltf here and this site will tell you which file it is looking for instead of showing you an empty viewer.

Buffers can also be embedded directly in the JSON as base64 data URIs, which makes the file self-contained but roughly a third larger than the equivalent GLB. Some exporters offer this as "embedded" or "single file" glTF.

When .gltf is the better choice

• When you want to read or edit it. It is JSON: you can inspect the node

tree, rename things, or fix a material by hand.

• In a build pipeline, where the .bin is compressed and cached

separately by a CDN, and the JSON changes more often than the geometry.

• For debugging. A glTF validator's complaints are much easier to act on

when you can see the structure.

Units, materials and structure

All identical to GLB, because it is the same format in a different container: metres by specification rather than by declaration, physically based materials, a real node hierarchy with transforms, and instancing.

See the GLB page for the details. Everything there applies here.

Converting to and from glTF

Because glTF is metres and most engineering formats are millimetres, every conversion between them applies a factor of 1000. This site does that automatically and states the factor on the conversion report, because a part that arrives 1000 times too large or too small is the single most common complaint about glTF in an engineering context.

Converting to glTF from a format with an assembly tree (3MF, COLLADA, STEP) keeps the tree, because glTF has real nodes. Converting to STL or PLY flattens it.

Version 1.0

glTF 1.0 exists and is obsolete. It used GLSL shaders directly and is not compatible with 2.0 tooling. This site reads 2.0 only and says so if handed a 1.0 file.