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21st-design-sync

21st-design-sync is a skill for Claude Code, Codex from 21st-dev/skill. It costs 129 tokens per session (1,388 once invoked), scanned A, original, Apache-2.0.

A tool-assisted workflow for publishing an existing project's light and dark design variables as a public theme on 21st.dev, a community theme library.

In plain words
What is it for?
Use it when you want to publish a project's design tokens as a shareable 21st.dev theme.
Why use it?
It packages the project's existing visual settings for sharing, while checking for the required API key and source CSS file first.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

not rated 34repo +1 1mo ago A scan Socket: passSnyk: fail 129 tokens original Apache-2.0

Good fit Use it when you want to publish a project's design tokens as a shareable 21st.dev theme.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/21st-dev/skill/21st-design-sync
View source ↗ 21st-dev/skill
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add 21st-dev/skill --skill 21st-design-sync
Clone the repo
git clone --depth 1 https://github.com/21st-dev/skill

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for 21st-design-sync

README.md
[![agentmods](https://agentmods.dev/badge/skills/21st-dev/skill/21st-design-sync/github.svg)](https://agentmods.dev/skills/21st-dev/skill/21st-design-sync)
Your own site
<a href="https://agentmods.dev/skills/21st-dev/skill/21st-design-sync"><img src="https://agentmods.dev/badge/skills/21st-dev/skill/21st-design-sync/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for 21st-design-sync

Your own site · 80×15
<a href="https://agentmods.dev/skills/21st-dev/skill/21st-design-sync"><img src="https://agentmods.dev/badge/skills/21st-dev/skill/21st-design-sync.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 129 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,388 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • Socket pass 11 Jul 2026
  • Snyk fail 11 Jul 2026
How audits are shown
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00129 $0.01388
Opus 5.5 $0.00052 $0.00555
Sonnet 5.5 $0.00026 $0.00278
Haiku 4.5 $0.00013 $0.00139

Measured 2mo ago against content hash 65cc94c842e0, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

21st-design-sync scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

Copies of this mod

2 near-identical copies found in the catalogue:

skills/21st-design-sync/SKILL.md · 121 lines

How it starts

The opening of the file, as written. The whole thing — 121 lines — stays where its author put it; the contents beside it link to each section on GitHub.

21st Design Sync — publish your project's design as a theme

Take the design a project already ships (its light + dark CSS variables) and publish it to the public 21st.dev theme library so anyone can preview, bookmark, and apply it. Under the hood this is one CLI call: 21st publish-theme <file.css> --name "…".

Pre-flight (always)

  1. Auth needs a real API key. publish-theme is a management endpoint: it accepts a 21st_sk_… key only, not a 21st login session token. Get one at https://21st.dev/mcp (or https://21st.dev/settings/api-keys) and pass it via --api-key 21st_sk_… or the TWENTYFIRST_TOKEN / API_KEY_21ST env var. If the user has no key, point them there — don't try to mint one.
  2. The CLI is the unified @21st-dev/cli (bin 21st). Use npx @21st-dev/cli if it isn't installed.
  3. Publishing is public and outward-facing. A published theme is immediately is_public in the community library (there is no unlisted/private option for themes). Confirm with the user before publishing.

Step 1 — Find the project's design tokens

Locate the file that defines the shadcn/Tailwind theme variables. Check, in order:

  • app/globals.css, src/app/globals.css
  • src/index.css, styles/globals.css, app/styles/globals.css

You're looking for a :root { … } block of CSS custom properties (--background, --foreground, --card, --primary, --secondary, --muted, --accent, --destructive, --border, --input, --ring, the --chart-* / --sidebar-* tokens, --radius) and a matching .dark { … } block. Values may be hsl(...), oklch(...), hex, or raw channels — keep them exactly as the project wrote them.

Tailwind v4 projects usually keep the same :root / .dark blocks plus an @theme inline mapping; you only need the :root and .dark token values, not the @theme mapping.

Step 2 — Assemble a valid theme CSS file

The publish endpoint parses --name: value; pairs out of a :root { … } block and a .dark { … } block, and requires both to be non-empty. So the file you publish must contain both.

Read the full file on GitHub · 121 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2mo ago First seen · 121 lines · 129 tokens per session scan A 65cc94c842e0

Subscribe to this mod's changes

21st-design-sync is a skill published in the GitHub repository 21st-dev/skill (34 stars, last pushed 1mo ago), licensed Apache-2.0. It adds 129 tokens to every session and 1,388 once invoked, about $0.0005 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

Design and UX
Related

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21st-design-sync next to 6 skills from other repositories
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