LlamaIndex is a comprehensive Python framework designed for building Large Language Model (LLM) applications, with a primary focus on Retrieval-Augmented Generation (RAG) and agentic workflows. It functions as a modular library rather than a monolithic application, providing abstractions for data ingestion, indexing, retrieval, and query orchestration. The architecture is split between a core package (`llama-index-core`) containing base interfaces and logic, and a vast ecosystem of integration packages (`llama-index-integrations`) that connect to external LLM providers, vector databases, and data sources. The codebase demonstrates a strong plugin-based design, allowing developers to swap components like embeddings, retrievers, and LLMs without rewriting the core orchestration logic.
langchaingo is a Go port of the LangChain framework, providing a modular, composable library for building LLM-powered applications. In production, it serves as an abstraction layer over dozens of LLM providers (OpenAI, Anthropic, Google AI, AWS Bedrock, Ollama, HuggingFace, etc.), vector stores (Chroma, Pinecone, Weaviate, pgvector, Redis, Qdrant, and many more), and supporting components such as chains, agents, memory, tools, document loaders, and prompt templates. The architecture is a monorepo library: users import packages and compose interfaces (`Model`, `Chain`, `VectorStore`, `Agent`, `Memory`) to orchestrate LLM workflows. Key entry points are provider constructors (e.g., `openai.New()`) and composition functions (e.g., `chains.NewLLMChain()`, `agents.NewExecutor()`). The library relies on many external SDKs and databases, creating a large dependency surface. It includes a custom HTTP record/replay testing infrastructure (`httprr`) for deterministic testing of API calls. The codebase is actively maintained with recent commits and a large community, but carries medium technical drift due to some outdated dependencies and deprecated API patterns.