Head to head
Pencil (pen.dev) vs Spline
Pencil (pen.dev) and Spline solve the same job (AI design builders), so this is a pick-one decision. Pencil (pen.dev) is our default here: Names your exact stack as a first-class target — React + Tailwind + shadcn/ui. Draw the article template, and the drawing becomes real components. Because the .pen file lives beside the code, the design and the build cannot silently drift. Watch out: Requires a local checkout via Lovable's GitHub sync — cannot touch the browser editor. Domain is mid-rename (pencil.dev → pen.dev), early access, no published pricing commitment.
Quick read
- Free with no card: Pencil (pen.dev).
- Editor's pick: Pencil (pen.dev).
| Field | Pencil (pen.dev)pen.dev Not yet swept | Splineapp.spline.design Not yet swept |
|---|---|---|
| What it is | A Figma-like canvas inside Cursor/VS Code/Windsurf, storing designs as JSON .pen files inside your project folder so they are git-versioned next to the code. Runs as an MCP server, so the agent reads the canvas as structured design context rather than as an image. Two-way: you can import existing components back onto the canvas. | Real-time collaborative 3D in the browser with materials, timeline animation, physics, particles and event interactivity. Publishes a hosted .splinecode file consumed by a first-party React runtime. The Community gallery lets you remix existing scenes rather than modeling from zero. |
| Category | AI design builders | AI design builders |
| Cost tier | free | paid |
| Pricing | Free during early access | Free (watermarked) · $12–$120/mo |
| Why builders pick it | Names your exact stack as a first-class target — React + Tailwind + shadcn/ui. Draw the article template, and the drawing becomes real components. Because the .pen file lives beside the code, the design and the build cannot silently drift. | Best-in-class React embed story — but the heaviest thing on this list. A three.js-class runtime plus a scene file that routinely runs into megabytes. Use renderOnDemand, wrap in React.lazy, and never put it above the fold on a page where LCP matters. |
| Watch out for | Requires a local checkout via Lovable's GitHub sync — cannot touch the browser editor. Domain is mid-rename (pencil.dev → pen.dev), early access, no published pricing commitment. | No-watermark on web embeds is Pro ($20/mo yearly); Hobby only clears exports. Code/self-hosted export is Max-only at $120/mo. The React wrapper's last tagged release is v4.0.0 from June 2024. |
| How to wire it up | MCP server; assumes Claude Code as the agent | npm install @splinetool/react-spline @splinetool/runtime |
| Editor's pick | Yes | No |
Other matchups worth running
Agent endpoint: GET /api/public/compare?slugs=pencil,spline