21st Ai

21st AI — sketch, iterate & grab code from the terminal

21st AI is a fast UI-drafting board. Mental model: draft it here, then finish it — sketch a few variants from a prompt, preview them, refine the one you like with plain-English edits, and pull its code into the repo. The whole loop runs from the 21st CLI (or the matching MCP tools), so you never leave the editor.

Sketch mode produces self-contained HTML + Tailwind drafts (fast, no build). The recommended handoff is the copy-prompt: a spec that tells you to rebuild the design in the target project's real stack — not paste raw HTML verbatim.

Auth

Same credential as the rest of the CLI: 21st login (saved token) or a 21st_sk_ key via --api-key / TWENTYFIRST_TOKEN. 21st usage shows tier + remaining quota. (See the 21st-cli-use skill for the full auth notes.)

The loop

# 1) Sketch — generate variants ("takes") from a prompt. Opens the preview in
#    the browser and prints the projectId.
21st generate "a pricing section with 3 tiers and a monthly/annual toggle"

# 2) List the takes (1-based numbers + whether each has rendered yet).
21st generation 

# 3) Edit ONE take in place with a natural-language change (PAID — see Metering).
21st iterate  "make it enterprise-flavored, add an annual toggle" --take 3

# 4) Grab the code to bring into the project (FREE).
21st take  --take 3            # paste-ready copy-prompt (recommended)
21st take  --take 3 --code     # raw self-contained HTML instead

Open the preview URL (printed by generate, and returned by iterate) in the editor's built-in browser to watch the variants render and update in place.

When to use which

• generate — start fresh from a prompt. Returns a preview URL + projectId.
• generation — list the takes so you know which --take N to act on.
• iterate — refine an EXISTING take (edited in place; a new version is

appended, so you can step back in the workspace). Use this to change something already generated instead of starting over.

• take — pull a take's code. Default prints the copy-prompt (adapt-to-my-

stack spec); --code prints the raw HTML. Both FREE and unlimited.

Metering

• generate — small free daily bucket, then a paywall (21st usage shows

what's left). Community access / membership lifts it.

• iterate — billed by real token cost per edit (the shared 21st AI credit

pool); it does real model work each call, so batch changes into one clear instruction rather than many tiny ones.

• generation (listing) and take (grabbing code) are FREE.

MCP parity

The same loop is exposed as MCP tools for MCP hosts (Cursor, Claude Desktop, Claude Code): generate (with mode: "sketch"), get_generation, iterate_generation and get_take. iterate_generation also returns the freshly-edited html + copyPrompt, so you can grab the code without a second call. Wire up the server with 21st init --client --write.

Tips

• A sketch is a draft, not production code — treat the copy-prompt as a

design spec and rebuild it in the project's real components; don't paste the HTML as-is.

• Refer to takes by the 1-based number from generation / the "Take N" label in

the preview. --take must be a whole number ≥ 1 (a bad value errors rather than silently editing take 1).

• Only sketch generations you created can be listed, edited, or fetched.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: 21st-dev
• Source: 21st-dev/claude-code-plugin
• License: Apache-2.0

Install and usage instructions live in the source repository linked above.