Two bar patterns are worth knowing on the 5-minute SPY chart because they're simple and they mean something. An inside bar has a high and low within the prior bar's range — compression. An outside bar engulfs the prior bar — expansion. Together they read the market's rhythm: coiling versus releasing.
Inside bars: compression and coil
An inside bar (or a series of them) means the range is contracting — buyers and sellers in balance, energy building. It often precedes a breakout: the coil resolves with an expansion move in the direction it breaks. Inside bars at a level are a heads-up that a decision is coming — and a break of the inside bar's range is a low-risk entry trigger with a tight stop (the other side of the bar).
Outside bars: expansion and reversal
An outside bar — one that trades beyond both sides of the prior bar and closes strongly — signals expansion and often a reversal, especially at an extreme. It shows one side seizing control decisively (sweeping the prior bar's highs and lows). An outside bar at a wall or range extreme, closing against the prior move, is a reversal tell — related to a failed auction.
Inside bars coil; outside bars release. One says “a move is coming,” the other says “a move just happened — maybe the other way.”
How to use them
Use inside bars as coil-and-break triggers (trade the break of the inside bar in the trend's direction, or the ignition out of the coil) and outside bars as reversal confirmation at levels. Both are context patterns, strongest at a mapped level and with the regime — an inside-bar break at a wall, an outside-bar reversal at an extreme. Simple, but genuinely useful on the timeframe scalpers watch.