Paper
A design canvas where every element is real HTML and CSS, flexbox included, instead of a proprietary format. Direct consequence: your agent reads and edits your mockups in the language it already knows. The Paper Desktop app (macOS, in open alpha since March 2026) runs a local MCP server with 24 tools, read and write: from Claude Code, the agent creates an artboard (`create_artboard`), writes HTML into it (`write_html`), changes a text or a style, while you watch the canvas fill up.
Strengths
- Mockup and code speak the same language: no conversion that loses the layout
- The MCP writes as much as it reads: the agent builds on the canvas, it does not just inspect it
- Connects to Claude Code with one command, on a local server
Limitations
- Open alpha, desktop app on macOS only
- 100 MCP calls per week on the free plan: one serious exploration session burns through them fast
Best for
- Designers who vibecode and want to keep a canvas they can edit by hand
- Exploring several screens with Claude Code before writing the real product code