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.

What is the difference between a .vellum file and a .pen file?

Both are documents you keep beside your code. A .vellum file is deterministic JSON with a published specification, so the same document always produces the same bytes, which keeps diffs and merges predictable. pen.dev documents are .pen files in its own format.

Can I use Claude Code, Codex or Cursor with Vellum?

Yes. The vellum command is an MCP server, so any MCP client can design: Claude Code, Codex, Cursor, Gemini CLI, Windsurf, Copilot CLI, Zed and others. The built-in agent uses your own provider key instead.

How do I move a design from pen.dev to Vellum?

There is no .pen importer yet. Vellum imports Figma documents and web pages, and the .vellum specification is public, so a converter can be written against the same types the editor uses.

Alternatives / pen.dev

A pen.dev alternative that keeps the design in your repository

pen.dev, formerly Pencil, is an agentic design canvas that keeps .pen files next to your code, with on-canvas models, MCP and a command line. It is a real answer to a real problem: design work happens in the same place as the code, and an agent can drive the canvas.

Vellum does the same job with a different bet. The design is a plain JSON document in your repository, the canvas is open source, and every agent edit goes through one permissioned path that you can review turn by turn.

This page compares the two on the things that are hard to change later: what is on disk, what an agent is allowed to do, what you need an account for, and what it costs.

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What pen.dev does well

Local-first canvas and .pen files beside your code, in a desktop app, an IDE extension and a command line.
A model for every budget: hosted models included in the plan, or your own subscription or API key.
A broad drawing surface for a young tool: shaders, gradients, a pen tool, imports from live web pages and one-click HTML and CSS export.
The things a team expects around the canvas: share links, comments, versions and team workspaces.

What changes with Vellum

The canvas is open source

Everything Vellum runs is in the repository: the document model, the layout engine, the renderers, the daemon, the command line and the MCP server. Read it, build it, change it, or check a claim in the code. The licence is Apache-2.0.

The file is a small, deterministic JSON document

A Vellum document is one .vellum file. The same document always serializes to the same bytes, so a design diffs in a pull request like code, reviews as an image in Git, and rolls back with the branch it belongs to. The format has a published specification.

An agent has to be permitted, and the change is attributable

Agent writes go through one guard. You can see who changed what, stop a running agent, undo a whole turn or a single change, and lease a frame so two agents do not edit it at once. The history is per actor and stays in Git.

No account, no hosted model, no telemetry by default

Local design, export, the command line and MCP work signed out. Provider keys live in the system keychain, never in the file. The daemon listens on a user-only socket, not a network port, and telemetry is off until you turn it on.

One price instead of a per-seat plan

Free during the beta — no card and no charge now. After the beta, a one-time purchase — not a subscription. Date to be announced. Agents run on your own subscription or provider key, so the plan is for the application, not for model usage.

Vellum, pen.dev and Paper side by side

How the three canvases differ. Vendor facts were read from their public documentation and pricing pages on 5 November 2026.
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.

Where pen.dev is ahead

Sharing links, comments, versions and team workspaces are shipped there; in Vellum, collaboration is built but not attached to the editors yet.
Hosted models are included in the plan, so there is nothing to configure before the first prompt.
The drawing surface is further along in some areas: shaders, gradient types and importing a live web page as layers.

Choose Vellum when

The design file has to live in the repository, diff in a pull request and merge with the branch.
You want to read the canvas code, or your company needs an open-source licence.
Your agents already run on your own subscription or provider key and you would rather keep it that way.
A one-time price matters more than a monthly seat.

Choose pen.dev when

You want a hosted model included, with no key to arrange.
Share links, comments and team workspaces are a requirement today.
You want the widest drawing surface a young agent canvas offers.

pen.dev alternative: 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.
What is the difference between a .vellum file and a .pen file?: Both are documents you keep beside your code. A .vellum file is deterministic JSON with a published specification, so the same document always produces the same bytes, which keeps diffs and merges predictable. pen.dev documents are .pen files in its own format.
Do I need an account or a subscription to use Vellum?: No account is needed for local design, export, the command line or MCP. Free during the beta — no card and no charge now. After the beta, a one-time purchase — not a subscription. Date to be announced. Agents run on your own subscription or provider key.
Can I use Claude Code, Codex or Cursor with Vellum?: Yes. The vellum command is an MCP server, so any MCP client can design: Claude Code, Codex, Cursor, Gemini CLI, Windsurf, Copilot CLI, Zed and others. The built-in agent uses your own provider key instead.
How do I move a design from pen.dev to Vellum?: There is no .pen importer yet. Vellum imports Figma documents and web pages, and the .vellum specification is public, so a converter can be written against the same types the editor uses.

Where these facts come from

Vellum statements are checked against its own documentation. Facts about pen.dev come from pen.dev, its documentation and its pricing page, read on 5 November 2026. Vendors change their plans; check theirs before you decide.

This page is written by the Vellum project. It says where pen.dev is ahead, and it links to the vendor for anything it does not state.

Bring your next screen into the repository.

Open a file, describe the screen, and watch an agent draw it beside your code.

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