Best LLM Frameworks in 2025: LangChain vs LlamaIndex vs Vercel AI SDK

LLM Frameworks Simplify AI Development

Building with LLMs involves more than API calls. You need prompt management, context handling, streaming, and often RAG (Retrieval-Augmented Generation).

Quick Comparison

Vercel AI SDK: Web-First

The Vercel AI SDK is optimized for React and Next.js applications.

Key Features

• Streaming UI - built-in React components
• Provider agnostic - OpenAI, Anthropic, etc.
• Edge ready - works in edge functions
• Type-safe - full TypeScript support
• Simple API - minimal boilerplate

Example

```tsx import { useChat } from 'ai/react';

export default function Chat() { const { messages, input, handleInputChange, handleSubmit } = useChat();

return ( <div> {messages.map(m => ( <div key={m.id}>{m.role}: {m.content}</div> ))} <form onSubmit={handleSubmit}> <input value={input} onChange={handleInputChange} /> </form> </div> ); } ```

Best For

• Next.js applications
• Chat interfaces
• Streaming responses

LangChain: The Swiss Army Knife

LangChain provides extensive tooling for complex LLM applications.

Key Features

• Chains - compose multiple LLM calls
• Agents - autonomous decision-making
• Memory - conversation history
• Tools - extend LLM capabilities
• Integrations - 100+ data sources

Example

```typescript import { ChatOpenAI } from '@langchain/openai'; import { HumanMessage, SystemMessage } from '@langchain/core/messages';

const chat = new ChatOpenAI({ modelName: 'gpt-4' });

const response = await chat.invoke([ new SystemMessage('You are a helpful assistant.'), new HumanMessage('What is the capital of France?'), ]); ```

Best For

• Complex AI workflows
• Agent-based systems
• Multiple data sources

LlamaIndex: RAG Specialist

LlamaIndex excels at connecting LLMs with your data.

Key Features

• Data connectors - ingest from anywhere
• Indexing - efficient retrieval
• Query engines - natural language queries
• Agents - data-aware agents
• Evaluation - measure quality

Example

```typescript import { VectorStoreIndex, SimpleDirectoryReader } from 'llamaindex';

const documents = await new SimpleDirectoryReader().loadData('./data'); const index = await VectorStoreIndex.fromDocuments(documents); const queryEngine = index.asQueryEngine();

const response = await queryEngine.query('What is in my documents?'); ```

Best For

• Document Q&A
• Knowledge bases
• Search applications

Choosing the Right Framework

Decision Framework

Choose Vercel AI SDK if:

• Building web applications
• Need streaming UI
• Want simplicity

Choose LangChain if:

• Building complex chains
• Need agents
• Multiple integrations required

Choose LlamaIndex if:

• Building RAG applications
• Document search/Q&A
• Knowledge management

Our Recommendation

• Web apps: Vercel AI SDK
• Complex AI: LangChain
• RAG/Search: LlamaIndex
• Simple API calls: OpenAI SDK directly

Explore AI tools in our Tools directory or compare options with our Compare tool.

Sources

• Vercel AI SDK
• LangChain Documentation
• LlamaIndex Documentation