glTF viewer that opens the .bin as well

Then give it the .bin. A .gltf is a JSON description that keeps its vertex data in a separate binary buffer, usually called scene.bin, and its textures as ordinary image files beside it — that is the format working as designed, not a broken export. Select both files at once in the dialog, or drag the whole folder onto the page, or drag a zip of it: the references are resolved against the files you handed over, in memory, with nothing fetched and nothing uploaded. Re-exporting as .glb still works and is the better thing to send other people, but it is no longer something you have to do just to look at the model.

Because a repository is not an inbox. The separated form keeps textures as ordinary PNG files that can be diffed, replaced and version-controlled independently, and the JSON is human-readable, so a material tweak is a text edit rather than a re-export. Pipelines typically author in .gltf and ship in .glb. The rule of thumb: .gltf while a model is being worked on by people who share a filesystem, .glb the moment it leaves that filesystem.

It is the third packaging of the same format: a .gltf whose buffers and images are written inline as base64 data URIs instead of as file references. It opens here with no siblings needed, exactly like a GLB, and it is the easiest fix if your exporter offers it. The cost is size — base64 inflates binary data by about a third, which is precisely why GLB exists as the binary alternative.

Yes, byte for byte after decoding. They are two containers for one format, and every feature — the PBR material model, the node hierarchy, morph targets, animation, extensions — is expressible in both. Converting between them rearranges packaging and touches nothing about the mesh, which is why gltf-transform can do it losslessly in either direction and why a viewer can treat them with the same parser, as this one does.

Check the line under the file name: it says whether this page found textures, vertex colours or no colour data. Grey with “no colour data” usually means the image files were not part of what you dropped — the geometry came through the .bin while the textures had nowhere to come from. The list of files used is printed above the measurements, so compare it with the folder. Grey with “textured” means the textures loaded but are themselves plain, which happens with placeholder materials from a modelling package.

Partly, and it says which. Draco compression and KTX2 textures both need extra decoders that this page does not ship, and both produce a named error explaining that rather than failing silently. The material extensions that three.js implements natively — clearcoat, transmission, sheen and the rest — are honoured when present. Anything unknown is ignored by the loader, which is what the specification requires: a viewer must render what it understands and not refuse the file.