LangChain4j

Free

LangChain for Java ![GitHub Repo stars](https://img.shields.io/github/stars/langchain4j/langchain4j?style=social)

FreeFree tier

Type

Open Source

Visit Website GitHub (40 stars)

About LangChain4j

LangChain4j is an idiomatic, open-source Java library for building LLM-powered applications on the JVM. It offers a unified API over popular LLM providers and vector stores, and makes implementing tool calling (including MCP support), agents and RAG easy. It integrates seamlessly with enterprise Java frameworks like Quarkus and Spring Boot. The library provides a modular architecture with extensive integrations for many LLM providers (OpenAI, Azure OpenAI, Anthropic, Google Gemini, Mistral AI, Ollama, etc.) and vector stores (Pgvector, Milvus, Chroma, Elasticsearch, etc.), along with support for document loading, parsing, and transformation, embedding models, and guardrails.

Key Features

Unified API over popular LLM providers and vector stores

Tool calling including MCP (Model Context Protocol) support

Agent-based patterns and RAG (Retrieval Augmented Generation)

Seamless integration with enterprise Java frameworks (Quarkus, Spring Boot)

Modular architecture with 50+ modules for LLMs, vector stores, document loaders, and more

Built-in support for chat memory, streaming, and tool execution

Guardrails and observational capabilities (micrometer metrics)

Support for local models via Ollama, LLaMA, and ONNX scoring

Pros & Cons

Pros

Idiomatic Java design with a clean, fluent API
Open source with a permissive license and active community (12.7k+ stars)
Comprehensive integration with major LLM providers and vector stores
First-class support for enterprise Java frameworks (Spring Boot, Quarkus)
Modular and extensible architecture allows selective dependency management
Actively maintained with frequent releases and strong documentation

Cons

Java/JVM only, not usable from other programming languages
Smaller ecosystem and community compared to Python-based LangChain
Documentation and examples may still be maturing for advanced features
Requires familiarity with Java and JVM ecosystem

Best For

Building conversational AI and chatbots on the JVMQuestion answering over proprietary documents with RAGAutomated code generation and analysis in enterprise Java applicationsCreating AI agents that can use tools and call external APIsIntegrating LLM capabilities into existing Spring Boot or Quarkus microservices

FAQ

What is LangChain4j?

LangChain4j is an open-source Java library that provides a unified API for building LLM-powered applications on the JVM. It supports popular LLM providers and vector stores, and makes it easy to implement tool calling, agents, and RAG.

Does LangChain4j integrate with Spring Boot and Quarkus?

Yes, LangChain4j is designed to integrate seamlessly with enterprise Java frameworks like Quarkus and Spring Boot.

What LLM providers does LangChain4j support?

LangChain4j supports many LLM providers including OpenAI, Azure OpenAI, Anthropic, Google Gemini, Mistral AI, Ollama, Hugging Face, Cohere, and more.

Is LangChain4j free to use?

Yes, LangChain4j is open source and free to use. It is available under an open-source license (typically Apache 2.0, as per GitHub repository default).