Why Not LangChain

This is not a criticism of LangChain. It is a positioning statement.

Different Goals

	LangChain / LlamaIndex	RAG Axis
Primary goal	Rapid prototyping, broad coverage	Production correctness, explicit contracts
Failure handling	Generic exceptions, often silent	Named types, mandatory signals
Cost tracking	Optional, plugin-based	Core return type on every result
Adapter boundary	Class inheritance	typing.Protocol, zero coupling
Abstraction philosophy	Abstract complexity away	Make complexity explicit and manageable
Target user	Anyone building with LLMs	Engineers owning production RAG systems

When to Use LangChain

• You need a working prototype in hours
• You are exploring capabilities across many providers
• You are building a demo or tutorial

When to Use RAG Axis

• You are building a RAG system that will be in production
• You need per-stage cost and latency visibility
• You need retrieval failures to be named, typed, and catchable
• You need your pipeline to be independently testable at every stage

warning

RAG Axis is not a drop-in replacement for LangChain. It is a different tool for a different job.