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, MCP, and Developer Tools.

21st’s developer surface includes documentation, getting-started guide, engineering blog, pricing, signup flow, changelog, CLI, and 13 more developer resources.

🌐 Visit website 📡 Profile data on GitHub

37.3/100 thin ▬ flat Agent 31/100 agent ready Front door AI 5/6 prominent Heartbeat 66/100 slowing saas Full breakdown ↓
scored 2026-11-06 · rubric v0.27.0 · Show this score on your site →

AccessPaid

0 APIs 1 MCP Servers 4 Agent Skills

Company UI Components React MCP Developer Tools Artificial Intelligence Agents Design Systems FrontendComponent Registry

Kin Score

Kin Score How this is scored →
scored 2026-11-06 · rubric v0.27.0

Composite quality — 37.3/100 · thin

Contract Quality 0.0 / 21

Developer Ergonomics 11.3 / 17

Access Clarity 13.0 / 17

Operational Transparency 2.0 / 11

Contract Governance 0.0 / 10

Discoverability 5.0 / 9

Regulatory Posture 2.7 / 15

Agent readiness — 31/100 · agent ready

Machine-Readable Contract 0 / 18

Agentic Access Contract 0 / 10

Documented Reversibility 0 / 6

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

A2A Agent Card 0 / 8

Dry-Run / Simulate Mode 0 / 4

Delegated User Identity 6 / 6

Protected Resource Metadata 5 / 5

Registration Without a Human 6 / 6

Agentic Commerce Well-Known Document 0 / 5

Pagination 5 / 5

Distinct Operations 3 / 3

MCP Tool Quality 6 / 6

Regulatory Posture applies to this provider. Its tags matched the Horizontal (data, software, accessibility, platform) regime, so Regulatory Posture carries 15 points of the composite. If this regime is wrong for your business, say so on your provider repo — the applicability map is public and we will correct it.

Create-or-Update Ergonomics could not be measured. We hold no machine-readable contract for this provider to read, so there is nothing to measure a write surface against. Excluded rather than scored zero: never-measured and measured-empty are different facts. Publishing an OpenAPI is what makes this facet — and several others — scorable at all.

The six quality facets above are damped to 85 points between them, because the conditional facet above carries the other 15. That is why each facet's contribution is shown against a damped maximum: raising a quality facet moves the composite by 85% of its nominal weight, not 100%. The full arithmetic is at apis.io/rating/.

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Agent readiness — checks not met, largest first (exact, from this profile):

Machine-Readable Contract +18 pts — api_specs includes an OpenAPI document
Agentic Access Contract +10 pts — agentic_access artifact present (x-agentic-access), graded by author
Idempotency +9 pts — OpenAPI mutating operations declare an idempotency key — a header, a request-body property, or a named de-duplication token whose own description says so (verified); else common[].type matches /idempoten/i (documented)
Stable Error Semantics +8 pts — OpenAPI $refs a shared error schema across 4xx/5xx responses (verified), else common[].type includes ErrorCatalog / ErrorCodes / DeclineCodes
A2A Agent Card +8 pts — a2a/-a2a.yml manifest, graded on conformance.grade against A2A 1.0.0
Rate-Limit Signaling +7 pts — OpenAPI responses document X-RateLimit-* / RateLimit headers (verified), else a rate_limits artifact or RateLimits link (documented)

7 more unmet checks in the Agent Readiness table above.

Kin Score — facets with the most composite points still available (weight × headroom):

Contract Quality scores 0.0 — up to +25.0 composite points
Contract Governance scores 0.0 — up to +12.0 composite points
Operational Transparency scores 18.4 — up to +10.6 composite points

Each check links to what satisfies it. Publish the artifact, or tell us where it already lives, and the score moves on the next scoring run.

Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. Every facet and dimension name above is a link: it opens that measurement's own page — what it means, the exact checks that feed it, how the whole catalog distributes on it, and the providers at the top of it. This rating is computed from the provider profile at artifacts.apis.io/21st/apis.yml: open an issue on github.com/api-evangelist/21st to ask a question or point us at an artifact you publish. Submit an artifact on GitHub — free → Manage your own listing — the Influence plan, $499/mo →

Markets this provider is in provisional

The Kin Score Market layer reads a provider inside its market: its position, and how deep its integrations go. Depth is only comparable within a position. Provisional and unweighted: not part of the Kin Score or agent readiness.

Market	Position	Depth	Registered MCP server	Declares compatibility
Agent Skills (SKILL.md packages)	distribution	19.2 (thin)	1	2

Registered MCP server and declares compatibility are report only — not weighted. Undeclared means we found nothing we can read, so there is no number: we never infer integrations.

Standards implemented 4

Standards this provider implements or carries. De facto ones are profiled and measured by the API Commons; formal ones come from the standards directory and are linked by the provider's own tags. The evidence column says how each claim was established — not that it was made.

Model Context Protocol (MCP)

measured — observed by APIs.io (verified)

Agent Skills

measured — observed by APIs.io (published)

OAuth 2.0 Protected Resource Metadata

measured — observed by APIs.io (verified)

Dynamic Client Registration

measured — observed by APIs.io (published)

MCP Servers 1

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

21st MCP Server

Remote MCP server at 21st.dev.

MCP SERVER

Agent Skills 4

Packaged agent skills for driving this provider's APIs from an AI assistant.

21st-ai

AGENT SKILL

21st-cli-use

AGENT SKILL

21st-design-sync

AGENT SKILL

21st-registry

AGENT SKILL

21st API pricing

Prices published by 21st, read 2026-10-07 from 21st.dev/pricing.

Plan	Price
Builder	$6 per month billed yearly per user Includes: Unlimited code & prompt copies, 29,000 icons, MCP & CLI search, unlimited component installs; no mon
Builder + AI	$15 per month billed yearly per user Includes: 500–2,000 AI credits/mo, Design Bug Bot included, everything in Builder
Team	$7.50 per seat/ month billed yearly per seat (2–50 seats) Includes: Centralized billing, shared collections, admin controls, private team components, optional AI credit

Plan details, limits and sources →

Pricing Plans 1

Published pricing tiers and plan structures.

21St Plans Pricing

3 plans

PLANS

Security Posture 2

Authentication, domain security, vulnerability disclosure, and trust-center signals.

21St Authentication

apiKey · 1 scheme

SECURITY

21St Domain Security

TLSv1.3 · HSTS · DMARC

SECURITY

Resources

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 4

Pricing, plans, and the legal terms of use

Plans

Pricing

TermsOfService

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
deliveryModel:
  model: saas
  open_source: false
  commercial: true
  callable_host: false
  label: Hosted service · you call their endpoint
  confidence: medium
  source:
  - pricing
  generated: '2026-08-28'
  method: derived
accessModel:
  pricing: paid
  onboarding: unknown
  trial: false
  try_now: false
  public: false
  label: Paid
  confidence: medium
  source:
  - plans
  - authentication
  - security
  generated: '2026-11-06'
  method: derived
specificationVersion: '0.23'
created: '2026-07-17'
modified: '2026-07-17'
image: https://21st.dev/opengraph-image.png
tags:
- Company
- UI Components
- React
- MCP
- Developer Tools
- Artificial Intelligence
- Agents
- Design Systems
- Frontend
- Component Registry
tags_raw:
- Company
- UI Components
- React
- Model Context Protocol
- Developer Tools
- AI
- Agents
- Design Systems
- Frontend
- Component Registry
apis: []
common:
- type: Plans
  url: plans/21st-plans-pricing.yml
- 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

21st API — frequently asked questions

How do I authenticate with the 21st API?

21st documents its authentication (apiKey · 1 scheme). The details are profiled on APIs.io as 21St Authentication.

How much does the 21st API cost?

21st publishes its prices; its Builder plan is $6 per month billed yearly per user as of 2026-10-07. APIs.io lists 3 pricing plans for 21st, with each plan's price, limits and inclusions under Pricing on this page.

Does 21st have an MCP server?

Yes. APIs.io lists 1 MCP server for 21st: Remote MCP server at 21st.dev.

Is the 21st API ready for AI agents?

21st has a Kin Score of 37.3 out of 100 (thin) and an Agent Readiness score of 30.9 (agent-ready), scored by API Evangelist on 2026-11-06.

Work with this as data

Every provider here is available over the APIs.io API and to AI agents over MCP.

MCP server

One button, every client — Claude, Cursor, VS Code and the rest.

https://apis.io/mcp

Tools for providers

9 MCP tools reach this

find_providersBrowse and filter every provider in the catalog.
get_provider_artifactsEvery artifact this provider publishes, grouped by type.
get_provider_operationsEvery operation across all of their OpenAPIs — one call instead of parsing every spec.
get_provider_toolsEvery MCP tool they ship, with the operation each wraps.
get_provider_evidenceHow each part of their score was established. Free — the basis for a claim should not sit behind it.
get_provider_ratingPRO — composite, band, trend and facet scores.
apis_io_searchSTART HERE — APIs, providers and tags for one query, each with its total.
resolveTurn a domain, URL or GitHub org into the provider it belongs to.
find_cohortsEvery scored population of providers in the catalog.

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