21st (YC Winter 2026)

TL;DR: 21st is a Y Combinator Winter 2026 startup UI building blocks for the agentic internet, currently active with a team of 3.

UI building blocks for the agentic internet

YC ID
31123
YC Batch
Winter 2026
Status
Active
Team size
3
Industry
B2B, Engineering, Product and Design
YC profile
https://www.ycombinator.com/companies/21st

Last verified:

21st.dev is the largest React component registry for AI applications, used by 2M developers We provide the building blocks to create agent-powered apps: UI components, agent templates.

Built by LemStudio

Building or buying SaaS? Try our founder tools →

Frequently asked questions

Is 21st a YC (Y Combinator) company?

Yes. 21st was funded by Y Combinator in the Winter 2026 batch. UI building blocks for the agentic internet

What does 21st do?

21st.dev is the largest React component registry for AI applications, used by 2M developers We provide the building blocks to create agent-powered apps: UI components, agent templates.

What YC batch was 21st in?

21st was part of Y Combinator's Winter 2026 batch.

How big is 21st?

21st has a team of 3 people according to Y Combinator's directory.

Is 21st still active?

21st is currently listed as Active with a team of 3 in Y Combinator's directory.

More YC Winter 2026 companies

More B2B YC startups

Explore related YC hubs

Loading interactive view…