The Short Answer
Use Spline when a designer needs to make a simple 3D scene quickly and the 3D is one element on the page. Use Three.js when the 3D is central to the site, must run well on mid-range phones, or has to react to products, scroll or data. Many studios use both: Spline or Blender to explore the idea, Three.js to ship it.
What Each One Is
Spline is a browser-based 3D design tool. Designers build scenes visually, add simple interactions and animation, and embed the result in a website with a few lines of code or a no-code builder. Three.js is an open-source JavaScript library that developers use to build 3D scenes in code; it powers a large share of the 3D sites that win awards.
The difference is who is in control. With Spline the tool decides much of what loads and how; with Three.js the developer decides everything, which is more work and more power.
Side by Side
| Spline | Three.js | |
|---|---|---|
| Who builds it | Designer, no code needed | Developer |
| Speed to first scene | Hours | Days |
| Control over loading and size | Limited | Complete |
| Performance on low-end phones | Depends on the scene, hard to tune | Can be tuned precisely |
| Scroll-driven animation | Basic | Precise, usually with GSAP |
| Connect to products, CMS, data | Limited | Anything |
| Cost model | Subscription, plan-dependent features | Free library, paid developer time |
When Spline Is the Right Call
Spline is the right call for a single decorative hero object, an early prototype to test an idea with stakeholders, a portfolio or event page with a short life, or a team with designers and no 3D developer. It is the fastest way from idea to something moving on screen.
Check the plan before you launch. Features such as code export and removing Spline branding depend on the plan, and they change over time.
When Three.js Is the Right Call
Three.js is the right call when the 3D carries the page: a product viewer customers rely on, a scroll-told launch story, a configurator tied to real variants, or anything that must hold a smooth frame rate on a mid-range Android phone. It is also the right call when SEO and Core Web Vitals matter, because the developer can delay the 3D until after the page has loaded.
The trade-off is cost: Three.js work needs a developer who understands both 3D and web performance, which is why we compared hiring a Three.js developer versus a 3D studio.
The Hybrid Most Studios Use
In practice the tools are not rivals. A common workflow is to sketch the scene in Spline or Blender, agree the motion with the client, then build the final version in Three.js with models exported from Blender as compressed GLB files. The client gets the speed of a visual tool at the start and the control of code at the end.
What About AI Tools?
AI coding assistants can now generate a Three.js scene from a prompt, and some builders generate Spline-like scenes too. They are useful for prototypes; they do not yet replace the modelling, optimisation and testing that make 3D work on real phones. We tested this in can you make a 3D website with AI.
Working With Kalex
Kalex prototypes freely and ships in Three.js, with models made in Blender. See our 3D website service or read how a 3D website gets built.