25 side-by-side comparisons of the concepts interviewers ask about most. Understand the tradeoffs, know when to use what, and never confuse the two again.
Prompt engineering shapes a single turn; reach for agents only when a task genuinely needs tools, state, and multiple steps. Good prompts are a prerequisite either way.
Native function calling is the fastest way to give one provider's model tools; MCP standardizes those tools so they work across any client without a rewrite.
ReAct interleaves thought and action turn by turn; plan-and-execute drafts the whole plan up front, then executes it. Plan-and-execute is cheaper on long tasks; ReAct adapts better to surprises.