LangChain

LangChain has established itself as the de facto standard framework for building LLM-powered applications. Its modular architecture excels at chaining together prompts, tools, and memory into sophisticated agent workflows. The RAG capabilities are particularly impressive, with extensive document loaders, text splitters, and vector store integrations that make retrieval-augmented generation accessible out of the box.

The framework supports virtually every major LLM provider through a unified API abstraction, making it easy to swap models without rewriting application logic. Prompt templating and management are well-designed, though the learning curve can be steep given the rapidly evolving API surface"breaking changes between versions remain a common frustration.

LangSmith adds valuable MLOps capabilities for tracing, debugging, and evaluating chains in production, though the paid tiers ($39/seat/mo) add up for larger teams. The open-source core is genuinely free and community-driven, with excellent documentation and an active ecosystem.

Limitations include occasional over-abstraction that can obscure what's happening under the hood, and performance overhead compared to lighter alternatives like LlamaIndex for pure RAG use cases. Still, for comprehensive LLM application development, LangChain remains the most versatile choice available.