Alternatives
Design canvases for agents, compared
A new kind of design tool appeared with coding agents: a canvas the agent can read and write, sitting next to your code. pen.dev, Paper and Vellum are three answers to the same question, and they differ in what they put on disk, what an agent is allowed to do, and what they cost.
This page compares them on the decisions that are expensive to reverse. Every vendor statement comes from its public documentation or pricing page, read on 5 November 2026.
Beta downloads coming soonThe three canvases
Vellum
Open-source vector canvas with the design file in your repository, agent writes behind one permissioned path, and no account for local work.
pen.dev
Agentic canvas with .pen files beside your code, on-canvas models, MCP, a command line and team features around the canvas.
Paper
Connected canvas for teams shipping with agents, where frames are HTML and CSS and agents join over MCP.
Side by side
| What to compare | Vellum | pen.dev | Paper |
|---|---|---|---|
| Design file | One .vellum file of plain JSON in your repository. | .pen files kept on your computer beside your code. | A canvas of real HTML and CSS, synced with your codebase. |
| Source and licence | Open source, Apache-2.0: canvas, daemon, CLI and MCP server. | A vendor application; see pen.dev for its terms. | A vendor application; see Paper for its terms. |
| Account | Not needed for local design, export, the command line or MCP. | Sign in to the app. The free plan includes 5 days a month designing with an agent. | An account in the browser app. The free plan includes unlimited editors. |
| Agents | Any MCP client or the built-in agent. Writes go through one permissioned path, with per-turn history and undo. | On-canvas models, hosted or with your own key, and MCP for external clients. | IDE and command-line agents over MCP, with in-app agent setup. |
| Team collaboration | Not in the editors yet. | Share links, comments, versions and team workspaces. | A multiplayer canvas; editors are free on the free plan. |
| Price | Free during the beta. Then USD 59.99 once, not a subscription. | Free tier. Pro is USD 16 per user a month; Ultra is USD 48; enterprise on request. | Free plan. Pro is USD 16 per editor a month billed yearly, USD 20 monthly; organizations on request. |
| Platforms | Desktop app, VS Code extension, command line and MCP server. | Desktop app, IDE extension and command line. | Desktop app and the browser. |
Alternatives: questions
Is Vellum an alternative to pen.dev and Paper?
- Vellum is an open-source design canvas for you and your coding agents, with files in your repository. It competes with pen.dev and Paper on the same job: describe a screen, watch an agent draw it, steer it, then take the code. The three differ in what they put on disk, whether an account is required, how agent edits are permitted and what they cost.
Which design canvas should I choose for agents?
- Choose Vellum when the design file has to live in the repository, the agent work has to be reviewable change by change, and you want an open-source canvas with no account. Choose pen.dev for hosted models and a broader in-app feature surface, or Paper when the canvas should be HTML and CSS and your team works in the browser.
Does Vellum import pen.dev or Paper files?
- Not yet. Vellum imports Figma documents and web pages, and exports its own format and code. The .vellum format has a published specification, so a converter can be written against the same types the editor uses.
How this page is written
The Vellum project maintains this page. Vellum claims are checked against its own documentation; pen.dev and Paper claims come from their public sites, documentation and pricing pages, linked on each comparison page. Where a competitor is ahead, the page says so.
Sources: pen.dev, pen.dev documentation, pen.dev pricing, paper.design, Paper documentation and Paper pricing.
Put the design where the code lives.
Open a file, describe the screen, and watch an agent draw it in your repository.