21st

21st (21st.dev) is a Y Combinator-backed company building an open, community-driven registry of crafted React, Next.js and Tailwind CSS UI components, plus the tooling to generate and consume them with AI. Its flagship product, Magic MCP, is an AI agent that drops into Cursor, Windsurf, Cline, VS Code and Claude Code to generate production-ready UI components from natural-language prompts. The platform also ships a remote hosted MCP server, the @21st-dev/cli terminal client, a private component registry CLI, published Agent Skills, and the @21st-sdk toolkit for building, deploying and embedding AI coding agents. Founded by Serafim Korablev and Sergey Bunas, 21st lets teams bring craft and taste back to digital products and build UIs that reflect their own design vision rather than generic LLM output.

21st is profiled on the APIs.io network. Tagged areas include Company, UI Components, React, Model Context Protocol, and Developer Tools.

21st’s developer surface includes documentation, getting-started guide, engineering blog, pricing, signup flow, changelog, CLI, and 12 more developer resources.

🌐 Visit website 📡 Source on GitHub

32.4/100 thin ▬ flat Agent 26/100 agent aware Full breakdown ↓
scored 2026-07-27 · rubric v0.5

AccessSelf serve

0 APIs 1 MCP Servers

CompanyUI ComponentsReactModel Context ProtocolDeveloper ToolsAIAgentsDesign SystemsFrontendComponent Registry

Kin Score

Kin Score How this is scored →
scored 2026-07-27 · rubric v0.5

Composite quality — 32.4/100 · thin

Contract Quality 0.0 / 25

Developer Ergonomics 13.9 / 20

Commercial Clarity 8.9 / 20

Operational Transparency 2.7 / 13

Governance 0.0 / 12

Discoverability 6.8 / 10

Agent readiness — 26/100 · agent aware

Machine-Readable Contract 0 / 18

Agentic Access Contract 0 / 15

MCP Server 12 / 12

Machine-Readable Auth 10 / 10

Idempotency 0 / 9

Stable Error Semantics 0 / 8

Request/Response Examples 0 / 7

Rate-Limit Signaling 0 / 7

Typed Event Surface 0 / 6

Agent Skills 5 / 5

Well-Known Catalog 0 / 4

Consent & Bot Identity 0 / 3

Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. This rating is computed from github.com/api-evangelist/21st: open an issue to ask a question, or submit a pull request to add artifacts. Want it done for you? Prioritized profiling — $2,500 →

MCP Servers 1

Model Context Protocol servers that expose these APIs to AI agents.

Get Started 3

Portal, sign-up, and the first successful call

DeveloperPortal

DeveloperPortal

GettingStarted

GettingStarted

SignUp

SignUp

Documentation 1

Reference material describing how the API behaves

Documentation

Documentation

Agent Surfaces 3

MCP servers, agent skills, and machine-readable catalogs

MCPServer

MCPServer

LLMsTxt

LLMsTxt

AgentSkill

AgentSkill

Build 4

SDKs, sample code, and the tooling you integrate with

GitHubOrganization

Packages

SDKs

CLI

Access & Security 2

Authentication, authorization, and security posture

Authentication

Authentication

DomainSecurity

DomainSecurity

Operate 1

Status, limits, changes, and where to get help

ChangeLog

ChangeLog

Commercial 3

Pricing, plans, and the legal terms of use

Pricing

Pricing

TermsOfService

TermsOfService

PrivacyPolicy

PrivacyPolicy

Company 2

The organization behind the API

Website

Website

Blog

Blog

Source (apis.yml)

aid: 21st
name: 21st
description: 21st (21st.dev) is a Y Combinator-backed company building an open, community-driven registry of crafted React,
  Next.js and Tailwind CSS UI components, plus the tooling to generate and consume them with AI. Its flagship product, Magic
  MCP, is an AI agent that drops into Cursor, Windsurf, Cline, VS Code and Claude Code to generate production-ready UI components
  from natural-language prompts. The platform also ships a remote hosted MCP server, the @21st-dev/cli terminal client, a
  private component registry CLI, published Agent Skills, and the @21st-sdk toolkit for building, deploying and embedding
  AI coding agents. Founded by Serafim Korablev and Sergey Bunas, 21st lets teams bring craft and taste back to digital products
  and build UIs that reflect their own design vision rather than generic LLM output.
url: https://raw.githubusercontent.com/api-evangelist/21st/refs/heads/main/apis.yml
x-type: company
x-source: vc-portfolio
x-backed-by:
- y-combinator
x-tier: stub
x-tier-reason: portfolio-lead
accessModel:
  pricing: unknown
  onboarding: self-serve
  trial: false
  try_now: false
  public: false
  label: Self-serve signup
  confidence: medium
  source:
  - authentication
  generated: '2026-07-22'
  method: derived
specificationVersion: '0.20'
created: '2026-07-17'
modified: '2026-07-17'
image: https://21st.dev/opengraph-image.png
tags:
- Company
- UI Components
- React
- Model Context Protocol
- Developer Tools
- AI
- Agents
- Design Systems
- Frontend
- Component Registry
apis: []
common:
- type: Website
  url: https://21st.dev
- type: DeveloperPortal
  url: https://21st.dev
- type: Documentation
  url: https://docs.21st.dev
- type: GettingStarted
  url: https://21st.dev/magic
- type: Blog
  url: https://21st.dev/blog
- type: Pricing
  url: https://21st.dev/pricing
- type: SignUp
  url: https://21st.dev/magic/console
- type: TermsOfService
  url: https://21st.dev/terms
- type: PrivacyPolicy
  url: https://21st.dev/privacy
- type: GitHubOrganization
  url: https://github.com/21st-dev
- type: ChangeLog
  url: changelog/21st-changelog.yml
- type: MCPServer
  url: mcp/21st-mcp.yml
- type: Packages
  url: packages/21st-packages.yml
- type: SDKs
  url: packages/21st-packages.yml
- type: CLI
  url: cli/21st-cli.yml
- type: LLMsTxt
  url: llms/21st-llms.txt
- type: Authentication
  url: authentication/21st-authentication.yml
- type: DomainSecurity
  url: security/21st-domain-security.yml
- type: AgentSkill
  url: skills/_index.yml
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io
x-enrichment:
  date: '2026-07-19'
  status: backfilled
  pass: local-v1
  note: backfilled from .gitignore signal + verified work evidence