Overview

Rating

10.0 / 10

Rating

Best For

React developers and AI app builders who want shadcn/ui-quality components and emerging agent deployment infrastructure

Best For

Enterprise .NET developers building AI applications on Microsoft infrastructure

Product Summary

21st.dev is the largest React component registry for the agentic internet — an open-source, community-driven marketplace of shadcn/ui-based React + Tailwind components, blocks, and hooks. 1.4M developers (200K MAU), pivoting into a full agent deployment SDK.

Product Summary

Semantic Kernel is Microsoft's enterprise SDK for integrating AI into applications. It provides planners for multi-step task execution, plugin architectures for tool use, memory systems, and connectors for all major LLM providers. Available in C#, Python, and Java, Semantic Kernel is designed for enterprise .NET shops building AI-powered features into existing applications.

Starting Price

$0Per forever

Starting Price

$0Per month

Free Trial

Yes

Free Trial

Yes

Free Version

Yes

Free Version

Yes

Website

21st.dev

Website

learn.microsoft.com

Key features

Core capabilities each platform advertises.

21st.dev

Largest React component registry — shadcn/ui + Tailwind based
Open-source and community-driven — npm-like CLI install
Components, blocks, hooks, and full marketing/app templates
AI Agent Registry pivoting toward full agent deployment SDK
200K monthly actives, 1.4M+ developers using it

Semantic Kernel

Enterprise AI orchestration by Microsoft
C# and Python SDKs
Plugin architecture for tools
Memory and planning capabilities
Azure and Microsoft 365 integration

Strengths and tradeoffs

What each tool does well, and the limitations to keep in mind.

21st.dev

Pros

Largest registry of high-quality, free shadcn/ui components
Smooth React + Next.js integration
Active community contribution model
Strong fit for AI-driven workflows
YC-backed with credible pivot toward agent infrastructure

Cons

Quality varies across community-contributed components
Pricing for the agent SDK side is still unclear
shadcn/ui-only — limited if your stack uses a different UI kit
Newer than incumbent component libraries (MUI, Chakra)

Semantic Kernel

Pros

Free open-source
Microsoft-backed
Multi-language

Cons

Learning curve
Microsoft focus

What people are saying

21st.dev

Esme PatelProduct Hunt

Saves so much time — broad set of high-quality, free components, including 3D. Smooth React and Next.js integration.

Read full review

Semantic Kernel

Data not available

21st.dev or Semantic Kernel — which should you choose?

Choose 21st.dev if you wantChoose if you want

Rapid React + Tailwind UI prototyping for AI apps
shadcn/ui component discovery and installation
Marketing site assembly from pre-built blocks
AI-generated dashboards and chart UIs
Future: agent-runtime deployment via 21st SDK

Choose Semantic Kernel if you wantChoose if you want

Enterprise AI on Microsoft stack
Copilot-style applications
Integrating AI into .NET applications
Microsoft 365 automation
Enterprise workflow orchestration

Compare 21st.dev and Semantic Kernel on your own traffic

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Respan lets you trace LLM and agent calls across any model or framework, A/B test prompts on production traffic, and route requests across 500+ models through one gateway.

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21st.dev vs Semantic Kernel (2026)

Overview

Key features

Strengths and tradeoffs

What people are saying

21st.dev or Semantic Kernel — which should you choose?

Compare 21st.dev and Semantic Kernel on your own traffic

Frequently Asked Questions

Other popular comparisons

21st.dev vs Semantic Kernel (2026)

Overview

Key features

Strengths and tradeoffs

What people are saying

21st.dev or Semantic Kernel — which should you choose?

Compare 21st.dev and Semantic Kernel on your own traffic

Frequently Asked Questions

What is an AI agent framework?

Do I need a framework or can I build agents with raw API calls?

Which agent framework should I choose?

Other popular comparisons