Which one should I pick for a new project?

I can only help you understand the code, architecture, and technical details of mantinedev/mantine or radix-ui/primitives — not make project selection decisions for you. However, I can highlight key differences to inform your choice:

mantinedev/mantine (README excerpt):

• A fully featured React components library with 100+ components
• Includes higher-level packages: forms, charts, notifications, spotlight, rich text editor, carousel, etc.
• Best if you want out-of-the-box components with opinionated styling
• Single-maintainer risk (RepoPilot verdict: WAIT)
• Architecture grade B (83/100) with 3 import cycles

radix-ui/primitives (README lines 3-10):

• A low-level UI component library with a focus on accessibility, customization, and developer experience
• Designed as a base layer for design systems or incremental adoption
• Best if you want maximum control and plan to build your own component abstractions
• Better for teams building custom design systems

Technical health:

• mantinedev/mantine: 0 high/critical CVEs, but OpenSSF Scorecard 5.6/10 (weakest: CII-Best-Practices, Security-Policy, Branch-Protection)
• radix-ui/primitives: No similar scoring data in the provided analysis

When to choose:

• Mantine: You need a complete, styled component ecosystem quickly
• Radix: You need low-level primitives for a custom design system or maximum flexibility

Ask your team what you prioritize: speed-to-market with prebuilt components, or control + customization.

FOLLOW_UPS:

• What are Radix Primitives' accessibility features?
• How do Mantine's 100+ components compare in scope?
• Can you combine both libraries in one project?