Chapter 09

Market Replay & Backtesting

Market Replay lets you rewind the market and replay historical trading days bar-by-bar. It's the closest thing to a time machine for traders — practice making decisions with past price action without knowing the outcome in advance.

Why Replay?

Live markets only give you one chance per day. Replay lets you practice dozens of sessions in a single evening:

  • Repetition: Trade the same day multiple times with different strategies to see what works
  • Pattern recognition: Relive price action around key levels — support breaks, resistance tests, opening drives
  • Speed control: Slow down volatile moments to study micro-structure, speed up quiet periods
  • No hindsight bias: When the chart unfolds bar-by-bar, you can't cheat by seeing the future

How Market Replay Works on QuantEdge

QuantEdge provides market replay in two places: the Paper Trading tool and the Options Chain Monitor. Both use real 1-minute intraday data from Yahoo Finance.

Paper Trade Replay

  1. Enter the Replay tab on the Paper Trading page. Select a ticker and a historical date.
  2. Press Play — the chart advances one bar at a time. The underlying price updates in real time and all your positions are re-priced using Black-Scholes.
  3. Place trades mid-replay — buy or sell options as the day unfolds. Your P&L updates with each tick.
  4. Set Entry & Target prices — limit entries auto-open when the spot reaches your entry price. Target prices auto-close positions when hit. Watch the automation execute without manual intervention.
  5. Use speed controls — 1x for real-time, 5x for moderate speed, 25x to zip through quiet periods.

Options Chain Replay

The Options Chain Monitor also has a Replay button. When activated:

  • The entire chain recalculates using Black-Scholes at each replay bar — premiums, Greeks, DEX, GEX, and VEX all update in real time
  • The chart shows key forecast levels (Support, Resistance, Max Pain, GEX Magnet, Target) as dashed lines
  • The Market Summary and Price Forecast re-run at each bar so you can see how the analysis evolves as price moves
  • You can study how dealer positioning shifts intraday — watch GEX flip from positive to negative as price moves through key strikes

What to Practice During Replay

1. Opening Range Breakouts

The first 15–30 minutes often set the day's range. Replay the open and practice identifying:

  • The initial balance (first 30-min high/low)
  • A breakout above the opening high — go long calls
  • A breakdown below the opening low — go long puts
  • Set your target at the expected move level from the forecast

2. Support/Resistance Bounces

Use the Options Chain to identify key levels (highest put OI = support, highest call OI = resistance). During replay, watch for price to approach these levels and observe the bounce or break.

3. GEX Magnet Plays

The GEX magnet strike tends to pull price toward it — especially in positive gamma environments. During replay:

  • Note the GEX magnet strike from the forecast
  • If price is below the magnet, buy calls expecting a drift toward it
  • If price is above, buy puts expecting a pull-down
  • Set your target at the magnet strike

4. IV Crush Events

Replay days around known events (FOMC, earnings). Watch how IV drops after the event (vanna flows), and how premium collapses on long positions. Practice selling options before the event and buying them back afterward.

The Science of Deliberate Practice

Research on expert performance shows that deliberate practice — focused, repetitive training with feedback — is what builds skill. Market replay provides all three components:

  • Focus: You choose specific setups to practice (breakouts, reversals, gamma plays)
  • Repetition: Replay the same scenario multiple times with different approaches
  • Feedback: Real-time P&L and trade history show you exactly how each decision played out
Ten replay sessions where you focus on one specific setup will teach you more than a month of watching live markets passively.

Replay vs. Backtesting

Backtesting runs a strategy automatically across historical data and gives you statistics (win rate, Sharpe, drawdown). Replay is different — it makes you the decision-maker, bar by bar.

  • Backtesting answers: "Does this rule-based strategy work over 1,000 trades?"
  • Replay answers: "Can I execute this strategy in real time with discipline?"

You need both. Backtesting validates the edge. Replay builds the skill to capture it.

Tips for Effective Replay Sessions

  1. Pick one setup per session. Don't try to trade every signal on a replay day. Focus on one pattern (e.g., "I will only trade GEX magnet bounces today").
  2. Start at 1x speed. Don't rush. Let the bar unfold and practice reading the chart in real time before speeding up.
  3. Review after each replay. Check your trade history. What worked? What didn't? Would you take the same trades again?
  4. Replay different market regimes. Practice on trending days, range-bound days, and high-volatility days. Each requires different tactics.
  5. Keep a journal. Write down what you learned from each session. Patterns you noticed, mistakes you made, rules you want to add.

Market replay is the bridge between theory and live execution. The more hours you spend in replay, the better prepared you'll be when real money is on the line.