Rebuilds the SPX dealer options book from the live tape: zero-gamma flip, call and put walls, hold band, and DEX/VEX/vanna/charm per strike. Positions are signed from trades, not the call/put convention. Volume, open interest and measured flow sit side by side, so you can see where they disagree. 1,000+ finished sessions are free forever, no account. A backtesting Lab and an MCP server come with it. No buy/sell signals.