
21st-ui-build
Build or substantially change production UI using the current project's design context, existing components, and grounded 21st inspiration. Use when implementing a page, section, component, responsive redesign, or visual polish in an existing web project. Trigger for requests such as "build this UI", "implement this screen", "make this page production-ready", or "use 21st to create the interface". Use 21st-ui-explore first when the visual direction is intentionally undecided, and 21st-ui-review for critique-only work.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/21st-dev/skill --skill 21st-ui-build- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads 21st-ui-build automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
Build project-aware UI
Preserve the product's identity while using 21st supply to accelerate implementation.
Workflow
-
Read
.21st/design.jsonand.21st/DESIGN.md. If neither exists, run21st init --design-context. -
Inspect the target route, its closest components, project instructions, and existing tokens. Treat explicit project facts as stronger than generic taste.
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Search before generating:
21st search "<specific UI need>" --context auto -
Reuse installed project primitives first. Retrieve or install a 21st result only when it reduces duplication or materially improves the result.
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If no result fits, check MCP
get_usage.aiGenerationEnabledor run21st usageand read the21st AI generationline. CLI 1.17.1+ also supports21st usage --json. Only when AI is explicitly enabled, generate project-aware alternatives using available AI credits:21st generate "<goal and constraints>" --context auto --variants 3Otherwise, implement alternatives with your own coding agent, grounded in
21st searchand21st get(MCP:searchandget_component). Do not call or suggest hostedgenerateoriterate_generationwithout AI access. -
Implement the selected direction in the project's real framework. Do not paste sketch HTML when the project expects React components, tokens, or established APIs.
-
Preserve responsive behavior, keyboard interaction, visible focus, semantics, reduced motion, loading states, empty states, and error states.
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Run the project's checks and
21st review <changed paths>. Apply only safe, deterministic fixes automatically.
Design rules
- Prefer project tokens over new arbitrary values.
- Prefer existing components over parallel lookalikes.
- Preserve established density, radii, typography, iconography, and layout rhythm unless the user explicitly requests a redesign.
- Use real product copy and states when available.
- Avoid decorative gradients, excessive cards, glass effects, huge headlines, and animation unless supported by the project or requested.
- Never claim a component, token, or capability exists without inspecting it.
Handoff
Report the direction used, reused 21st/project components, files changed, and
verification performed. Record a durable visual choice in
.21st/design.json under decisions when the user selects a new direction.
FAQ
What does the 21st-ui-build skill do?
Build or substantially change production UI using the current project's design context, existing components, and grounded 21st inspiration. Use when implementing a page, section, component, responsive redesign, or visual polish in an existing web project. Trigger for requests such as "build this UI", "implement this screen", "make this page production-ready", or "use 21st to create the interface". Use 21st-ui-explore first when the visual direction is intentionally undecided, and 21st-ui-review for critique-only work.
How do I install 21st-ui-build?
Run npx skills add https://github.com/21st-dev/skill --skill 21st-ui-build in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/21st-ui-build/ (personal) or .claude/skills/21st-ui-build/ (project).
Which AI agents can use 21st-ui-build?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is 21st-ui-build safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains 21st-ui-build?
It is published by 21st-dev in 21st-dev/skill. It has 1,409 recorded installs.
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