Given a new LLM use case, how do you decide between prompting, RAG, fine-tuning, and tools/agents?

The senior signal is matching the method to what is actually missing instead of defaulting to your favorite. Knowledge, behavior, or actions each point at a different tool. Here is the decision framework that scores highest.

Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.