Online 3D Viewer

Free, open source browser viewer that opens STEP, STL, OBJ, glTF and 15 more formats locally, with nothing uploaded to any server.

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A PBR textured glTF model in the viewer, with the mesh list on the left and vertex, triangle and size details on the right.

Screenshot: 3D Tool Wiki

Overview

Online 3D Viewer, best known through its public instance at 3dviewer.net, is an open source browser viewer built by Hungarian developer Viktor Kovacs. It does two jobs: a zero install site where anyone can drop a model and inspect it, and an embeddable JavaScript engine that powers 3D preview inside Gitea, a WordPress plugin active on over 9,000 sites, the Orthanc medical imaging project and an Obsidian plugin. Its defining trick is parsing engineering CAD formats (STEP, IGES, BREP) directly in the browser through a WebAssembly build of OpenCascade, something that used to require desktop software or server side conversion. Just as distinctive is its privacy model: files are read locally by the browser and never uploaded anywhere, which makes it safe for NDA bound work. The core is MIT licensed and entirely free, funded by donations.

Key features

STEP, IGES and BREP in the browser

A WebAssembly build of the OpenCascade CAD kernel (occt-import-js) tessellates mathematical B-Rep geometry into WebGL meshes on your own CPU. Engineering formats open in seconds with no server side conversion.

Nothing is ever uploaded

Files are read by the browser's FileReader API in local memory and never leave your machine. That satisfies NDA and data governance rules that rule out cloud viewers for unreleased designs.

19 import and 8 export formats

Reads everything from STL, OBJ and glTF to FreeCAD, Rhino, IFC and dotbim files, and exports to eight formats, so it doubles as a free format converter.

Assembly tree inspection

Imported parts keep their original hierarchy instead of being merged. Expand the tree, isolate or hide components, and read triangle counts, bounding boxes and material properties per part.

Explode view and measurements

A slider driven explode view (added October 2025) separates assembly components for inspection, and the details panel computes dimensions, volume and surface area.

An embeddable open engine

The same MIT licensed engine embeds in any site or app. It ships inside Gitea's file preview, a 9,000+ install WordPress plugin, Orthanc medical imaging and an Obsidian plugin.

Pros and cons

What users consistently praise

Zero friction: no signup, no install, no upload, works on any OS with a modern browser
Browser native STEP, IGES and BREP parsing that most free viewers simply cannot do
Privacy by architecture: files are processed locally, so proprietary designs never leave the machine
Keeps assembly hierarchy intact for part level inspection, where many lightweight viewers flatten everything

What users consistently criticise

No clipping planes and no point to point measurement, which limits serious engineering inspection
Sharing by URL is defeated by CORS blocks on Google Drive and Dropbox links, a constant source of user frustration
Very large files exhaust browser memory and crash the tab rather than degrading gracefully
OBJ models appear white unless the .mtl and texture files are dropped in together, a common trap for newcomers

Recurring themes across third-party user reviews (G2, Capterra, TrustRadius).

Pricing

Is Online 3D Viewer free?

Online 3D Viewer is free and open source. There is no paid edition to upgrade to, and no feature is held back behind a licence.

Plan	Price	What you get
Everything	Free forever	The site and the engine are MIT licensed open source with no tiers, accounts or usage limits. Development is funded by donations on Patreon, Open Collective and PayPal.
For integrators	Free (license note)	The core is MIT, but the occt-import-js dependency that powers STEP/IGES/BREP parsing is LGPL-2.1, which commercial products bundling it must comply with.

checked 2026-07-14

Best for

3D printing hobbyists

The fastest way to sanity check an STL or 3MF before slicing: drag, inspect dimensions and normals, done. No account, no install.

Engineers reviewing CAD

STEP and IGES files open directly in the browser with assembly trees and millimetre dimensions, no seat of desktop CAD required.

NDA and security sensitive work

Because parsing happens locally and nothing uploads, it is one of the few web viewers usable for unreleased or export controlled designs.

Developers embedding a viewer

The MIT engine drops into product pages, wikis and internal tools without licensing fees, with a track record inside Gitea and WordPress.

Who should look elsewhere

Teams that need share links

There is no cloud backend, so there is no share button. Linking a model means hosting the file yourself on CORS friendly storage, which defeats non technical collaborators.

Massive BIM and plant models

Parsing happens in browser memory, so very large assemblies (roughly 100 MB+ STEP files) can stall or crash the tab, especially on laptops and phones.

Polished client presentations

Rendering is functional rather than glamorous. For marketing grade lighting, AR viewing and hosted galleries, platforms like Sketchfab fit better.

Frequently asked questions

Is it safe to open confidential CAD files on 3dviewer.net?

Yes. Despite the name, files are parsed locally by your browser using the FileReader API and are never transmitted to any server. The geometry stays in your machine's memory.

Why does my OBJ model show up white with no textures?

An .obj file only stores geometry. Colors and textures live in the companion .mtl file and image files, so you must drag the .obj, the .mtl and all texture images into the window together.

Why does a model load from my desktop but fail from a URL?

Loading by URL requires the hosting server to allow cross origin (CORS) requests. Google Drive and standard Dropbox links block them, so URL loading needs CORS friendly hosting like GitHub raw links or a properly configured S3 bucket.

How can it open STEP files without uploading them anywhere?

It bundles occt-import-js, a WebAssembly compilation of the OpenCascade CAD kernel. Your own CPU tessellates the mathematical B-Rep surfaces into triangles the browser can render.

Can I edit or repair models with it?

No. It is strictly a viewer and converter: you can inspect, hide parts, measure bounding boxes and export to another format, but there are no modeling, repair or sculpting tools.

Can I embed the viewer in my own website commercially?

Yes. The engine is MIT licensed, free for commercial use. One nuance: the STEP/IGES/BREP parser dependency is LGPL-2.1, so products bundling that module need to follow its linking terms.