Overview
Once UI 1.5 and Re_gent are two open-source tools that serve very different purposes in the modern development ecosystem. Once UI is a Next.js-exclusive design system that helps indie builders and small teams create expressive, alive-feeling user interfaces with minimal code. Re_gent, on the other hand, is a version control system for AI agent actions—it tracks what your coding assistant changed, which prompt caused it, and lets you roll back agent work across files and sessions.
Feature Comparison
| Feature | Once UI 1.5 | Re_gent |
|---|---|---|
| Primary Purpose | Design system and UI toolkit for Next.js apps | Version control for AI agent actions |
| Target Users | Indie builders, solo founders, small teams building web apps | Developers using AI coding assistants (Claude Code, Codex, etc.) |
| Core Technology | Next.js exclusive design system with 100+ components, theming engine, data visualization | Content-addressed storage tracking agent conversations and file changes |
| Key Commands | Copy-paste components, single-file theme management, Row/Column/Grid layouts | rgt log, rgt blame, rgt sessions, rgt undo |
| Integration | npm install @once-ui-system/core, works with Next.js | CLI tool, integrates with Claude Code, Codex, OpenCode (more planned) |
| Open Source | Yes, MIT license with Pro tier | Yes, Apache-2.0 license, free forever |
| Visual Effects | Weather, particles, matrix-style dots, real-time dashboards | Not applicable |
| Audit Trail | Not applicable | Full conversation history, prompt-to-code traceability, rollback capability |
| Learning Curve | Low - human-readable syntax, minimal code required | Low - familiar git-like commands |
Pricing
Once UI 1.5: Once UI is open-source under the MIT license, with a Pro tier that offers additional features. The website mentions "Get Pro" but doesn't list specific pricing. The open-source version includes 100+ components and single-file theming.
Re_gent: Re_gent is completely free forever under the Apache-2.0 license. There are no paid tiers or premium features mentioned. The project is in public alpha and actively looking for contributors.
Pros and Cons
Once UI 1.5
Pros:
- Reduces code by 70% with human-readable, machine-writable syntax
- 100+ pre-styled open-source components ready to copy and paste
- Single-file theme management with design tokens
- Built exclusively for Next.js with minimal setup
- Includes data visualization, real-time dashboards, and visual effects
- Strong community with Discord and public roadmap
Cons:
- Exclusive to Next.js—not usable with other frameworks
- Pro tier may limit advanced features for free users
- Focused on UI, not backend or agent management
Re_gent
Pros:
- Tracks AI agent actions with full audit trail (conversation history, file changes)
- Undo, blame, and replay agent sessions like git
- Free forever with Apache-2.0 license
- Works with multiple AI coding assistants (Claude Code, Codex, OpenCode)
- Content-addressed storage preserves history even after compaction
- Multiple agent sessions with zero conflicts
Cons:
- Currently in public alpha with limited tool support
- Only useful for developers using AI coding agents
- Requires learning new CLI commands
Verdict
Once UI 1.5 and Re_gent solve entirely different problems. Once UI is perfect for Next.js developers who want to build beautiful, expressive UIs with minimal code—it's a design system that makes your product feel alive. Re_gent is essential for developers who rely on AI coding assistants and need accountability, traceability, and rollback capabilities for agent-generated code. Choose Once UI if you're building a user-facing web app; choose Re_gent if you're managing AI-driven development workflows. Both are open-source and free to start.
Once UI 1.5
Re_gent