Zlim vs gltfpack at a glance
| Zlim | gltfpack | |
|---|---|---|
| Input formats | glTF/GLB, OBJ, STL, PLY, FBX, Collada, USD/USDZ, 3MF, STEP, Creo, CATIA | glTF / GLB only |
| Output | Optimized GLB | Optimized glTF / GLB |
| Geometry compression | Draco or meshopt, vertex quantization | meshoptimizer (quantize + compress) |
| Texture handling | KTX2 / Basis transcoding + mipmaps | KTX2 (via toktx / basisu) |
| Draw-call reduction | Mesh merging + material atlasing | Mesh merging (limited) |
| Interfaces | Hosted REST API, local CLI, MCP server | Local CLI (self-hosted) |
| Per-job reporting | Input/output bytes, faces, vertices | Console output |
| Cost | Subscription; free tier (25/mo) | Free, open-source (MIT) |
| Best for | Non-glTF inputs, managed pipelines, AI agents | You already have glTF and want a free, self-hosted CLI |
The key difference: what goes in
gltfpack is part of the meshoptimizer project — a superb, free tool for squeezing glTF/GLB. But it starts from glTF. If your source is a STEP assembly, a CATIA part, an FBX from a DCC tool, a USDZ, or an STL scan, gltfpack can't read it; you first need a separate converter (Blender, FBX2glTF, a CAD tessellator) to reach glTF, and only then can you optimize.
Zlim collapses that two-step chain into one pass: it ingests the "dirty" formats directly and emits an optimized GLB, so there's no converter toolchain to assemble and maintain. Under the hood Zlim can use meshopt too — the difference isn't the compressor, it's everything before it.
When to choose gltfpack
Your assets are already glTF/GLB, you're comfortable running a CLI in your own environment, and you want a free, self-hosted, dependency-light optimizer. gltfpack is fast, battle-tested, and hard to beat on price.
When to choose Zlim
Your inputs are CAD (STEP/Creo/CATIA), FBX, USD, STL, or a mix; or you want a hosted API (and an MCP server for AI agents) instead of managing a converter-plus-optimizer toolchain; or you need deterministic, reported output — the same input and preset producing byte-stable GLB with a measured reduction every run.
FAQ
Can gltfpack convert FBX or STEP to GLB?
No. gltfpack only reads glTF/GLB. To optimize an FBX or STEP file you must first convert it to glTF with another tool, then run gltfpack. Zlim reads those formats directly and returns an optimized GLB in one pass.
Does Zlim just wrap gltfpack?
No. Zlim is its own engine with format ingestion (including CAD tessellation), mesh merging, material atlasing, and KTX2 texture transcoding. It can use meshopt or Draco for geometry compression, but the ingestion and whole-budget optimization around it are what set it apart.
Is gltfpack free?
Yes — gltfpack is open-source (MIT) and free. Zlim is a subscription service with a free tier (25 optimizations/month); you're paying for format ingestion, the hosted API/MCP, and managed, reported output.
Try Zlim free
25 optimizations a month, no card required. Any format in, optimized GLB out.