C0

Open-source Gen UI pipeline. The Zero before One.

Thesys built C1 — a $49/mo black box Gen UI pipeline. We built C0 — the same pipeline, fully open source.

What is C0?

Zod schema → JSON Schema → LLM structured output → partial JSON streaming → component rendering.

That's the entire Gen UI pipeline. C1 charges for it. C0 opens it.

Quick Start

pnpm add @c0/react @c0/schema zod

import { z } from "zod";
import { defineComponent, buildResponseFormat } from "@c0/schema";
import { useGenUI } from "@c0/react";

const WeatherCard = defineComponent({
  name: "weather_card",
  description: "Display current weather information",
  schema: z.object({
    city: z.string(),
    temp: z.number(),
    condition: z.enum(["sunny", "cloudy", "rainy"]),
  }),
});

// That's it. C0 handles the rest:
// schema → JSON Schema → LLM structured output → streaming → render

Note: C0 is in early development. The API above is the target — implementation in progress.

Why C0?

	C1	Tambo	CopilotKit	C0
Open source	✗	✓	✓	✓
Framework-agnostic	✗	✗ (React)	✗ (React/Angular)	✓
Pipeline visible	✗	Partial	✗	100%
Self-hosted	Enterprise	✓	✓	✓
No cloud required	✗	✗	✗	✓

Packages

Package	Description
@c0/core	Framework-agnostic engine (partial JSON parser, event bus, validation)
@c0/schema	Zod → JSON Schema, defineComponent(), buildResponseFormat()
@c0/stream	SSE streaming middleware, partial JSON parsing
@c0/react	React bindings (useGenUI, GenUIProvider, StreamingMessage)

The Pipeline

┌─────────────┐    ┌──────────────┐    ┌─────────────────┐    ┌──────────────┐    ┌───────────┐
│ Zod Schema  │ →  │ JSON Schema  │ →  │ LLM Structured  │ →  │ Partial JSON │ →  │ Component │
│ (you write) │    │ (auto-gen)   │    │ Output (any LLM) │    │ Parser       │    │ Render    │
└─────────────┘    └──────────────┘    └─────────────────┘    └──────────────┘    └───────────┘
    @c0/schema         @c0/schema           your LLM              @c0/stream        @c0/react

Development

pnpm install
pnpm build
pnpm test
pnpm typecheck

License

MIT