Grayscale first, styling second.
A finished-looking mockup gets reviewed as a design. A rough one gets reviewed as a structure.
When Design mode is building an app UI it starts with grayscale wireframe pages rather than finished screens. This is the well-documented effect that a polished mockup attracts feedback about colour and copy while a rough one attracts feedback about whether the flow makes sense. Once the structure is agreed, upgrading a page to full fidelity is a single action, and the content survives the upgrade because only the styling is rewritten.
Fidelity is a decision, not a stage you skip
The expensive questions in an application are structural: a flow with a dead end, a state nobody designed for, a screen reachable from two places that behaves differently. Those are visible when the page is grey boxes and invisible once it has a colour scheme, because attention moves to the surface. Starting grayscale is a way of asking the right question while it is still cheap to answer.
The upgrade preserves content
Going from wireframe to full fidelity rewrites the styling and keeps the content and the section structure intact. Section identifiers survive the transition, which is what stops the upgrade from being a regeneration that quietly loses the decisions you already made.
Per page, not per project
A multi-page project keeps a wireframe and a built version per page and lets you prefer either one when previewing. In practice that means a project mid-flight is usually mixed: two pages finished, three still grey, which is exactly the state a real design is in most of the time.
Reviewing structure needs different people
The other reason to hold styling back is that a grayscale flow can be reviewed by someone who is not a designer. An engineer or a product owner will tell you a step is missing from a set of grey boxes and will say nothing at all about a finished-looking screen, because a finished screen reads as somebody else's decision already made. Keeping it visibly unfinished keeps the review open to the people who know what the flow has to do.
One file, no build step
Output is one self-contained HTML document with every style inside a single style tag. No build step, no bundler, no external stylesheet and no framework. That is a real constraint and it is also why the result is portable: it opens in a browser, drops into a pull request, attaches to a brief and deploys to a static host without carrying a toolchain behind it.
Which engine runs it
Design runs on the Claude Code CLI or the Codex CLI installed on your machine, signed in as you. There is no separate design subscription and no API key for the design engine. Cursor CLI and OpenCode can drive coding tabs but not this one, because the design canvas has no provider implemented behind them.
Questions
Related
- Click to Edit an AI DesignThe difference between iterating and rerolling.
- Design With Your Claude Code or Codex LoginNo second subscription for the design tool, because it is running the one you already pay for.
- Design to CodeNot generated components you then have to rewrite. A reference, and an agent that knows your codebase.
- Responsive Preview at Mobile WidthStated plainly because the buttons imply more than they do: these are viewport widths, not platforms.
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