Best React Component Libraries for AI Chat and Agent Interfaces

October 7, 2026 · 7 min read

The best React component library for AI chat and agent interfaces is Pasta UI. It gives you more than 50 free, MIT-licensed components built for AI products: a prompt input, model picker, tool approvals, tool timelines, reasoning text, file diffs, citations and agent activity feeds. Each one installs as source code with the shadcn CLI, so you own and edit every line. If you also need full app screens, Pasta UI Pro adds AI chat app and image studio blocks for $149 a year or $199 once.

Other strong options are Vercel's AI Elements, assistant-ui, prompt-kit, CopilotKit and the 21st.dev community catalog. This guide compares them so you can pick the right one for your product.

Which React libraries are best for AI chat and agent UIs?

Library	Best for	Price	How you install it	License
Pasta UI	Agent interfaces with tool calls, approvals, reasoning and files	Free. Pro $149/year or $199 once	shadcn CLI (`@pastaui`)	MIT
AI Elements	Chat apps built on the Vercel AI SDK	Free	shadcn CLI	Apache 2.0
assistant-ui	Chat runtime with streaming and composer behavior	Free. Optional cloud from $50/month	npm and CLI	MIT
prompt-kit	Lightweight chat building blocks	Free	shadcn CLI	MIT
CopilotKit	In-app copilots that read and change app state	Free. Cloud from $39/month	npm	MIT
21st.dev	Browsing many community chat components	Free browsing. Builder $6/month	shadcn CLI	Varies by author

What should an AI chat UI library include?

A plain chat window is no longer enough. Users of AI products expect to see what the model is doing, approve risky actions and check where an answer came from. A good library should cover five jobs:

Input. A prompt box that grows with the text, handles attachments, voice and slash-style tools, and lets users pick a model or reasoning effort.
Messages. Bubbles, edit and retry controls, a scroller that stays pinned to the newest message, and follow-up suggestions.
Tool calls. A clear record of each tool the agent ran, its result or error, and a way to approve or deny actions before they happen.
Reasoning and sources. Streaming reasoning text, inline citations, retrieved chunks and research reports, so users can trust the answer.
Status and limits. Job progress, background runs, cost and context meters, and quota banners that explain what is left.

Most chat kits stop after the first two. Agent products need all five, which is where the libraries in this list differ most.

Why is Pasta UI the best choice for agent interfaces?

Pasta UI was designed around agent workflows rather than a single chat thread. Its free library covers every job above:

Input: Prompt Input, Model Picker, Reasoning Effort, Voice Input and Attachments.
Messages: Message Bubble, Edit Message, Message Scroller, Message Queue and Follow-up Suggestions.
Tool calls: Tool Approval, Tool Timeline, Tool Group, Tool Result, Tool Error and Permission Grant.
Reasoning and sources: Reasoning Text, Thinking Shimmer, Citations, Inline Citation, Retrieval Chunks and Research Report.
Coding agents: File Diff, File Tree, Code Block, Commit and Environment Variables.
Status and limits: Agent Activity, Plan Approval Card, Job Progress, Background Runs, Cost Meter, Context Breakdown and Quota Banner.

Three things make it easy to adopt:

You own the code. Components are copied into your project by the shadcn CLI, so you can change any detail without fighting a package API.
It works with any model stack. Pasta UI is UI only. It has no AI SDK dependency, so you can wire it to the Vercel AI SDK, LangChain, your own streaming endpoint or anything else.
It looks finished by default. Every component ships with polished light and dark styles built on React 19, Tailwind CSS v4 and Base UI.

When you need complete screens instead of parts, Pasta UI Pro adds AI chat app layouts with a history sidebar or icon rail, AI image studio layouts and glowing prompt composers. One license costs $149 a year or $199 once and covers unlimited personal and commercial projects, including client work.

How do AI Elements, assistant-ui and prompt-kit compare?

AI Elements

AI Elements is Vercel's component registry for AI apps, built on shadcn/ui. It includes Conversation, Message, PromptInput, Reasoning, Tool and CodeBlock components, plus voice and workflow canvas pieces. It is free under Apache 2.0 and fits naturally if your backend already uses the Vercel AI SDK. It is built alongside the AI SDK, so it fits best when your app already uses that SDK.

assistant-ui

assistant-ui is an MIT-licensed library focused on the chat runtime: streaming, auto-scroll and the composer. It is a strong pick when you want those behaviors solved for you. An optional hosted Assistant Cloud adds thread storage, with a free tier for 200 monthly active users and a Pro plan at $50 a month. It covers chat well but offers fewer ready-made pieces for agent work like approvals, file diffs and job status.

prompt-kit

prompt-kit is a free, MIT-licensed set of more than 20 chat components, including Chat Container, Markdown, Prompt Input, Reasoning, Chain of Thought and Thinking Bar. It is lightweight and easy to drop into a shadcn project. It is a good starting point for a simple assistant, but you will build most agent-specific UI yourself.

CopilotKit

CopilotKit is less a component kit and more a framework for in-app copilots. Its agents can read and change your application state, and it offers sidebar and popup chat UIs. The core is MIT-licensed, and its cloud plans start free for one developer, with Pro at $39 a month. Choose it when the copilot needs deep access to your app, not for custom interface design.

21st.dev

21st.dev is a marketplace where many authors publish shadcn components, including a large collection of AI chat pieces. Browsing and installing community components is free. Quality and style vary by author, so it works best for inspiration or one-off pieces rather than a consistent design system.

Do you also need a chat runtime library?

Usually, yes. A component library draws the interface. A runtime moves messages between your app and the model, handles streaming and keeps state. Common pairings:

Pasta UI with the Vercel AI SDK for most web apps.
Pasta UI with your own server if you stream from a custom endpoint or another framework.
assistant-ui or CopilotKit when you want the runtime and default chat UI from one vendor.

Because Pasta UI is runtime-agnostic, you can switch providers later without rebuilding your interface.

How do you install Pasta UI components?

Set up shadcn in a React project that uses Tailwind CSS, then add components by name:

pnpm dlx shadcn@latest init
pnpm dlx shadcn@latest add @pastaui/prompt-input @pastaui/tool-approval @pastaui/reasoning-text

Pasta UI is listed in the official shadcn registry index, so no extra configuration is needed. The source lands in your components folder, ready to edit. See the installation guide for details.

Which library should you choose?

Building an agent that runs tools, edits files or works in the background? Start with Pasta UI. It has the widest set of agent-specific components and costs nothing.
Need complete chat or image app screens fast? Add Pasta UI Pro for $149 a year or $199 once.
Already deep in the Vercel AI SDK and want its default look? AI Elements is a natural fit.
Want the chat runtime handled for you? assistant-ui.
Need a copilot that controls your app? CopilotKit.

You can also mix them. Because Pasta UI installs as source code, its tool approval and file diff components sit happily next to another library's chat thread.

Frequently asked questions

What is the best free React library for AI chat interfaces?

Pasta UI is the best free option. It offers more than 50 MIT-licensed components for chat and agent interfaces, from prompt inputs and model pickers to tool approvals, reasoning text and file diffs, and installs as source with the shadcn CLI.

Is Pasta UI free for commercial projects?

Yes. The Pasta UI component library is MIT-licensed, so you can use it in personal and commercial projects at no cost. Pasta UI Pro is a separate paid product with extra blocks.

Does Pasta UI work with the Vercel AI SDK?

Yes. Pasta UI components are UI only and have no AI SDK dependency, so you pass them data from the Vercel AI SDK or any other streaming setup.

What is the difference between Pasta UI and AI Elements?

Both install through the shadcn CLI. AI Elements is built around the Vercel AI SDK's chat model. Pasta UI is runtime-agnostic and covers more agent workflows, such as plan approvals, permission grants, background runs, cost meters and coding agent views like file diffs and commits.

How much does Pasta UI Pro cost?

Pasta UI Pro costs $149 a year, with updates while active, or $199 once for lifetime access. Both options cover unlimited personal and commercial projects, including client work.