The controls
- Symbol, expiry and historical date. Choose what to analyse; backtest mode replays a past session and live updates refreshes the page.
- Strike range. For example ATM plus or minus 1 shows the ATM strike and one strike either side. A wider range creates more per-strike charts.
- Layout. Choose the chart height (such as Tall) and how many strike charts sit in a row on a desktop.
- Display switches. Show PCR line, show underlying, show candles, show full returned session, show call price, show put price and show OHLC chart.
- Reference panel. A small panel repeats the underlying level and the ATM strike so you can see which chart is the ATM one.
By default the view can include all returned snapshots; the full-session switch controls whether the chart is restricted to market hours.
The summary cards
| Card | Meaning |
|---|---|
| Latest spot | The underlying level at the latest snapshot, with its timestamp. |
| Visible call OI and visible put OI | Total open interest across the strikes shown, with the change since the first snapshot of the session. |
| Visible-range PCR | Put OI divided by call OI over the strikes shown, with the number of strikes analysed. |
These cards are calculated over the visible range only, so they change when you change the strike range.
Reading a strike card
Each strike has a header with its price (marked ATM for the at-the-money strike) and two labels, one for the call and one for the put, each paired with the open-interest change. For example a call labelled long buildup with a put labelled writing means call open interest grew with a rising call premium, while put open interest grew with a falling put premium.
Below the header are two charts. The call chart plots call open interest, the call price and the spot, with volume bars underneath. The put chart plots put open interest, the put price, the PCR line and volume, so you can see whether open interest moved with or against price.
How selling is inferred
Exchange data does not label trades as buyer- or seller-initiated, so the page uses a heuristic: falling premium together with rising open interest is consistent with writing. The same footprint can come from spreads, hedges or other participants, so treat it as a hypothesis.
| Pattern at a strike | Consistent with | Be careful because |
|---|---|---|
| Rising OI and weakening premium | Possible writing at that strike | Spreads, hedges and falling implied volatility can look identical. |
| Repeated activity while price fails to move through the level | A defended strike | A defended strike can fail suddenly when covering or directional demand accelerates. |
| Falling OI, expanding premium or a broken level | Possible covering | It could also be an expiry roll or a shifted defence level. |
| Activity moving to a neighbouring strike | Migration of the seller zone | Migration does not show whether the original seller made or lost money. |
A routine for testing a seller zone
- Start at ATM and a few strikes either side so the map stays relevant to spot.
- Read OI change and premium on both the call and the put side rather than one strike alone.
- Compare neighbouring strikes: concentration across adjacent strikes is more convincing than a single strike.
- Check the underlying: does price respect, test or break the level? Turn on candles or the OHLC chart to see the response in the same view.
- Use historical mode and the full-session timeline to confirm the pattern persisted rather than appearing once.
Limits
Round-number index strikes attract concentrated activity because liquidity is deepest there, so concentration at a round strike is partly structural. Weekly expiry rolls can move activity to the next contract or a new ATM strike. Seller positioning is useful only when tested against the actual price path and timing. For a chain-level view see the option chain guide, and for OI at key strikes the Call vs Put OI guide.