Market Screener (FNO Screener)

A Market Screener, often called an FNO Screener in the Indian derivatives context, scans the full list of NSE stocks and indices eligible for futures and options trading and ranks or filters them against criteria a trader defines, unusual volume, sharp change in open interest, proximity to a support or resistance level, or a skewed put-call ratio. Instead of manually checking each of the roughly 180-200 stocks in the F&O segment plus the major indices one by one, a screener surfaces the handful that meet a specific condition on any given day.

The most common screens retail traders run are built around open interest behavior, since it reveals what large participants are doing even when price alone doesn’t tell the full story. A stock showing rising price alongside rising open interest is typically flagged as a long buildup, while a stock rallying on falling open interest points to short covering rather than fresh conviction, and a screener that surfaces these patterns across the whole F&O list saves a trader from having to check every stock’s chain individually every morning.

Screeners are also used to hunt for options-specific opportunities beyond simple price movement. Filtering for strikes with sudden spikes in implied volatility can flag stocks anticipating news or results, while filtering by bid-ask spread helps a trader avoid illiquid strikes where slippage on entry or exit would eat into any edge the strategy has. Combining an open-interest screen with a volume screen is a common way to distinguish a move backed by genuine fresh positioning from one that’s simply thin and noisy.

The main caution with screeners is that they surface correlation, not causation, a stock appearing on a screen for unusual open interest change doesn’t tell the trader why it happened, whether it’s a hedge, a rollover, or a directional bet. Screener output should be treated as a shortlist for further research and confirmation, including checking the underlying’s own chart and news, rather than as a standalone signal to trade on.