Live now
Index readings from the same feed the Sahi terminal runs on. Open the live OI Heatmap to see this guide applied to today’s numbers.
- NIFTY — —
- BANKNIFTY — —
- SENSEX — —
What you will learn
- ARead the page in a minute
- BRead one tile and its colour
- CSet the views, time and replay
- DRead it without fooling yourself
- ↻Run a routine
- 3
- things on the plane: strike, time, depth of colour
- 4
- tables: Both, Calls, Puts, Straddle
- 3
- colour scales: Session, Each time, Each strike
- 15
- strikes drawn when the page opens
First 5 Minutes
The question What do I do first, if I read nothing else?
Do this first
- Open the OI Heatmap. Leave every setting as it is. Strikes run down the page and time runs across it. The page opens on Build-up colouring, where a tile's colour shows what its premium and Open Interest did.
- Read the verdict in the insight card at the top. It says which side, Calls or Puts, has added more Open Interest over the last 15 minutes. It is a description of a change, not a forecast.
- Scan the plane. Which side holds more Open Interest, and at which strikes? Calls are on the left and Puts are on the right. In Build-up colouring, green and red name the move of the premium, not the side.
- Find the market line across the middle. Strikes above it are above the spot price, strikes below it are below.
- Read one row outwards from the Strike column. The newest column is beside the strike; older columns run away from it. Is the Open Interest large only at the newest edge, or all the way out?
- Rest the pointer on a tile for half a second. The card names the build-up and shows the two moves behind it.
No time? Read the page map, then the traps. On an expiry morning? The expiry-day routine. Nothing is showing? The states checklist. On a phone? Read this.
Values in this guide are as of 15 October 2026, read from the source files listed in the Sources section. Anything this guide could not confirm is gathered once, in What we have not verified.
What the OI Heatmap Is
The question What does a heatmap show that the option chain does not?
One Picture of the Whole Chain Over the Session
The option chain shows Open Interest as numbers, one moment at a time. The heatmap puts the same numbers on a grid. Each row is a strike, each column is a stretch of the session, and each tile is the Open Interest at that strike at the end of that stretch. In Amount colouring (Customise, Tiles), a deeper colour is a larger number.
That makes two things easy to see. One is where Open Interest is large today. The other is whether it was always there or arrived in the last hour: deep only at the newest edge means recent, deep all along the row means there since morning.
| Direction | What it carries | Where to read it |
|---|---|---|
| Down | Strike price, highest at the top | The Strike column in the middle |
| Across | Time, one column for each time step (15 minutes or 1 hour); the newest column beside the Strike column | The clock labels in the header row |
| Depth of colour | In Build-up colouring (the default), what the premium and Open Interest did; in Amount colouring, the size of the Open Interest | Step 7, and the ⓘ Overview |
What It Does Not Do
- It does not forecast. A deep tile says many contracts are open at that strike. It does not say who holds them or where price will go.
- It does not show who is long or short. Every open contract has a buyer and a seller.
- It places no orders and gives no signals. The build-up names and the insight verdict describe what already happened between two readings.
- It shows one expiry at a time, for one underlying, on the latest trading day only. Earlier days are not drawn.
Where the Numbers Come From, and How Fresh They Are
The question How current is a tile, and what does the page need before it can draw anything?
- Stored readings. The plane is built from the readings stored for the day: about a row a minute for each expiry. The page re-reads them about once a minute while the market is open and the tab is visible. It also adds its own reading of the option chain, which is re-fetched about every 5 seconds.
- A column is the last reading in its step. With 15-minute columns, the column labelled 3:05 is the reading at 3:05, not an average of the 15 minutes. Each column is labelled with the clock time of that reading.
- The insight card prints the time of the reading it used. Quote that time when you note what the heatmap showed.
- Latest trading day only, from 9:15. Earlier days and readings before the open are not drawn. The browser keeps about 600 readings, a session and a half.
What the Page Needs Before It Can Show a Change
A change needs two readings. The oldest column on the plane has no earlier reading, so its change shows a dash and its build-up shows a dash. If only one reading exists, the plane is one column wide, every change is a dash and the insight card says Not measured. If no reading exists at all, the page says No session history yet. Pictures are in The States.
Five Words to Know Before the First Tile
The question Which few words must I know before a tile makes sense?
- Open Interest
- The number of option contracts still open at a strike. It rises when new contracts are opened and falls when contracts are closed. It is not the same as volume, which counts trades.
- Strike
- The price at which an option can be exercised. One row of the plane is one strike. The strike nearest the spot price is the ATM strike.
- Lakh and crore
- The page prints Open Interest as K (thousand), L (lakh, one hundred thousand) and Cr (crore, ten million): 44.58L is 4458000 contracts, 1.14Cr is 11400000. The guide calls them contracts, as the page does; whether they count lots or units is not yet confirmed.
- Build-up
- A name for what a contract's premium and Open Interest did together between two columns: Long Buildup, Short Buildup, Short Covering or Long Unwinding. Two-letter codes LB, SB, SC and LU sit in each tile.
- Premium and LTP
- The price of one option. LTP is the last traded price. The page uses the premium to name the build-up and prints it in the LTP columns beside the strike.
The full list is in the glossary. In this guide Calls and Puts are written in full. The code CE or PE appears nowhere on the page.
The Page Map
The question What am I looking at, and where do I start?
Read from the top down. The insight card says what changed. The plane shows where Open Interest sits and when it arrived. The market line says where price is. Step 7 says what the colours mean. The numbers below are on the figure; each links to its step.
123456789The page bar: what a tile leads with, and Customise
The question What does the capsule change, and where are the other settings?
The page bar holds a capsule, Open Interest | Change, and the Customise button. The capsule chooses what each tile leads with: the Open Interest held (default), or the change since the column before. The second figure on the tile swaps to the other one. Everything else is in Customise, which is the subject of Part C.
The round information button beside the page title opens a short help panel for this page, with a link to this guide. On a phone the Customise button is the settings button in the top bar.
The insight card: one sentence about what changed
The question Which side added more Open Interest, and over what period?
The card sits above the plane. Its closed row has a verdict, two chips, a trio of numbers and a stamp.
- Verdict. Which side changed more over the chosen window, summed over the strikes drawn. It gives the outcome first, then what happened: Bullish indications when the Put side leads, Bearish indications when the Call side leads, Mixed indications when it is even, followed by more puts added, more calls added, more calls closed, more puts closed, puts added, calls cut, calls added, puts cut or even change (on the Calls or Puts table alone, calls added, puts cut and so on). Green means the Put side leads, red means the Call side leads. It is Even change when the gap is within 12% of the two changes added together.
- Chips. Calls and Puts: the change since the previous close, summed over the strikes drawn.
- Trio. Puts minus Calls change over 5 minutes, 15 minutes and the day.
- Stamp. The time of the reading the card used.
The card is opened and read in full in Step 15. Its verdict is a comparison of two changes, not a view on direction: Trap 5.
The side row and the expiry
The question Which expiry is this, and how do I look at one side only?
The capsule in the middle names the expiry every tile belongs to, with its days to expiry (DTE) beside it. Press it to choose another expiry. Pressing CALL or PUT shows that side alone; the chip then fills and shows a cross, and pressing the cross returns to both sides. The same four choices, Both, Calls, Puts and Straddle, are in Customise (Step 12).
An expiry with no stored readings of its own is drawn from whatever the page holds for it. If that is only the current chain, you will see the one-column state described in The States.
The time header: which way time runs
The question Where is the newest reading, and what does the chip beside it say?
On both sides the newest column is beside the Strike column, and history runs outward: older Call columns are further left, older Put columns further right. Each header is the clock time of the last reading in that step. The chip Δ 15m (or 5m, 30m, 1h) under the newest time names the step each change is measured over: the change since the column before. The header stays in view when you scroll down a long plane. If there are more columns than fit, scroll sideways; both sides move together.
The strike column and the LTP columns
The question What are the tags beside a strike, and where do the prices come from?
The strike never moves when you scroll. Beside it are the LTP columns: Call price on the left, Put price on the right, each with its change on the day. While the page follows the latest reading these are the option chain's own prices, so they agree with the chain. When you replay an earlier reading they show that reading's price against the same previous close.
The Tags
| Tag | What it marks | How it is found |
|---|---|---|
| ATM | The strike nearest the spot price, with an amber wash across its row | The ATM strike of the newest reading |
| Support | A strike below price where Put Open Interest is concentrated | The Open Interest page's zone rule: Put bands at or below ATM within 12 strikes of the money, in bands of 3 strikes, scored with a weight that depends on days to expiry; the band's centre is snapped to the nearest strike |
| Resistance | A strike above price where Call Open Interest is concentrated | The same rule on Call bands at or above ATM |
| Max Pain | The strike where option buyers would collect least at expiry | The lowest total payout, over every strike of the expiry |
Support, Resistance and Max Pain are read from the whole expiry's reading, not only from the strikes drawn, so a tag can describe a strike that is not on the plane. Two more levels, the Put wall and the Call wall, are in the insight card only (Step 15). Each tag can be switched off in Customise (Step 14).
The switch Put minus Call Open Interest prints, under each strike, the Put Open Interest minus the Call Open Interest at the newest column: green when Puts are larger, red when Calls are. It is a difference at one strike, not a ratio.
The market line: where price is
The question Where is price, and how far does the market expect it to move?
A 3-pixel line crosses Calls, the Strike column and Puts, between the last strike above the spot and the first below it. It is the same line as in the option chain, and prints the same figures.
| Piece | What it prints | How it is made |
|---|---|---|
| Spot capsule | The price, its move on the day in points and percent, and Low and High of the day | The chain's spot against the previous close; the day's Low and High from the day's candles. The bar inside is filled from Low up to the price |
| ATM Straddle | A rupee figure and, in brackets, IV | ATM Call price plus ATM Put price, drawn only when both prices exist. IV is the mean of the two legs' implied volatility, to one decimal |
| Exp Move | ± a number and the band | The expected move is 0.85 times the ATM straddle (the chain's own conversion); the band is the spot minus and plus the expected move |
The straddle, the expected move, the implied volatility and the day's Low and High can each be switched off in Customise, Market line; the Spot price stays. In replay every figure is that reading's own. Why the expected move is 0.85 times the straddle is a product convention, listed in What we have not verifiednot yet confirmed.
The colours: what a deeper tile means
The question What does a deeper tile mean, and where is the key?
The page prints no key under the plane. The colour is set by Tile colour in Customise, and the page opens on Build-up: green where the contract’s premium rose, red where it fell, striped where positions were added, flat where they were closed, and a stronger colour for a bigger change (Step 9). Red and green there name the move of the premium, not the side. The side is named by the wing: Calls on the left, Puts on the right.
In Amount colouring deeper means larger: more Open Interest at that strike. Red is Calls and green is Puts, the side and not a rise or a fall in price. The ⓘ Overview says the same in one line: a deeper shade means a larger position within its wing, not a price direction, and colour does not predict the next price move. Step 10 shows what the code actually measures against. The Straddle table is grey.
One tile, part by part
The question What is printed in a tile, and what is it measured against?
One tile is one strike, one side and one time step. The page opens on Compact tiles; a Wide tile has two lines.
| Part | Example | Meaning |
|---|---|---|
| Figure | 1.14Cr | The Open Interest at that strike at the end of the column, in contracts: K thousand, L lakh, Cr crore. With the capsule on Change, the change leads here instead. |
| Build-up | Long Unwinding | Long Buildup, Short Buildup, Short Covering or Long Unwinding, written in full where the tile has room and as LB, SB, SC or LU in a compact tile, or nothing when there is no clear pattern. Beside the name, a Wide tile prints the change as a share of the strike’s Open Interest. A tile that carries an older reading says held. |
| Second figure | −78.7K | The change in Open Interest since the column before, with + or a true minus. It is the change over the step shown in the Δ chip, not over the day. |
| Price | (optional) | The contract's price at that time. Off by default; the switch is LTP in each tile. |
Calls are on the left of the Strike column and Puts on the right; in Amount colouring Calls are red and Puts are green. The two sides mirror each other: the newest column is beside the strike on both sides. The compact tile shows the same facts in less room: the code above the figure.
The build-up code: what the premium and Open Interest did
The question How is LB, SB, SC or LU decided, and what does it not say?
Each tile compares itself with the same strike and side in the column before, on two measures: the contract's price (premium) and its Open Interest.
| Premium | Open Interest | Name | Code | Plain reading |
|---|---|---|---|---|
| Up | Up | Long Buildup | LB | Fresh long positions are opening |
| Down | Up | Short Buildup | SB | Fresh short positions are opening |
| Up | Down | Short Covering | SC | Short positions are closing |
| Down | Down | Long Unwinding | LU | Long positions are closing |
| Unchanged, or no earlier reading | Either | No Clear Pattern | — | Nothing is claimed |
- There is no noise floor on this page. Any move, up or down, in either measure counts. A tile reads No Clear Pattern only when the premium or the Open Interest did not move at all, or when there is no earlier reading.
- The rule reads the contract's own premium. A Call and a Put follow the same arithmetic. A Put showing Long Buildup means Put premium and Put Open Interest both rose, which often goes with a fall in the underlying (or a rise in implied volatility), not a rise.
- The names are conventions. Open Interest cannot tell whether the people opening were buying or writing, or hedging another position.
The colour: from a number to a shade
The question How is a tile's depth worked out, and against what?
In Amount colouring a tile's depth is the square root of the ratio of its Open Interest to a maximum, mapped onto 16% to 80% of the side colour. The square root lifts small numbers so they do not vanish next to one very large tile. A tile at or past 68% turns its ink dark on Put and Straddle tiles so it stays readable.
What the maximum is depends on Customise, Tiles, Colour scale. All three take the maximum over Calls and Puts together:
| Scale | The maximum is | Use it to answer |
|---|---|---|
| Session (default) | The largest Open Interest of any tile on the plane, over the whole window | Which strikes are the heaviest today? How did one strike grow through the day? |
| Each time | The largest Open Interest in that column | At each time, which strikes were heaviest? The shape of the book at that moment |
| Each strike | The largest Open Interest of that strike over the window | When did each strike reach its own peak? Compares timing, not size |
Two Heatmaps Never Share a Scale
A deep tile on one underlying and a deep tile on another are not the same size. The shade is relative to a maximum that moves with the strikes drawn, the window and the scale chosen. Adding strikes, a new maximum or a change of scale re-colours every tile. The ⓘ Overview says tiles compare depth within each wing; in the code the maximum is shared by Call and Put, and the Straddle table has its own. not yet confirmed
Build-up Colouring
Build-up is the default Tile colour: the tile paints the pattern. Customise, Tiles, can switch it to Amount, which paints the size instead.
- Tone is the price leg: green where the premium rose, red where it fell. Here red and green mean the move of that contract's premium, not the side. The wing, left or right, names the side.
- Texture is the Open Interest leg: striped means positions were added, flat means positions were closed.
- Strength is the size of the change on the same three scales. A held tile and a No Clear Pattern tile take no colour.
A tile with nothing new: the dash and "held"
The question Why does a tile show a dash, or the word held?
The Dash: a First Reading
A change needs an earlier reading. The oldest column of the plane has none, so its tiles show a dash for the change and no build-up code. Choosing a short window makes this easy to see: in Last 30 min the oldest column, at the outer edge of each wing, is all dashes.
Held: a Reading That Is Carried Forward
If a strike has no row in one reading, the tile repeats that strike's last reading and says held. It carries no build-up and no colour wash in Build-up colouring. A held tile is not new activity, and its change reads 0.
Resting a pointer on such a tile says so: No new reading, Carried forward, not new activity (see Step 16). The next tile after a held tile compares itself with the held value.
Choose what to see
Which setting answers which question, and what does each one change?
Customise, and the four tables
The question How do I open Customise, and what does the Table choice do?
Press Customise in the page bar. A panel opens, docked to the bar. Every change applies to the plane at once, so there is no Apply button. Reset returns every setting to its default, the cross closes the panel, and Escape does the same. Your choices are remembered in this browser (the key is oiHeatmapSettings); Session replay is never remembered.
| Table | What the plane shows | Use it to |
|---|---|---|
| Both | Calls | Strike | Puts in one scroller, newest beside the strike on both sides | Compare the two sides at the same strike |
| Calls | Call tiles only, with the strike column on their right | Read the Call build without the Put colours |
| Puts | Put tiles only, the strike column on their left | The same for Puts |
| Straddle | Call and Put at each strike added into one grey tile; the straddle price under the strike | See where the combined position sits, whatever the side |
A Straddle tile adds the two legs' Open Interest, premium and changes. If either leg is held, the pair is held. The Straddle has its own colour maximum, because a pair of legs is larger than a single leg. Its hover card words the pairing as straddle buyers or straddle writers adding or closing.
Time: the step, the window and Session replay
The question How much of the day do I see, and how do I look back?
Each Column: 15 minutes or 1 hour
The step sets how much time one column covers. The default is 15 minutes. A column shows the last reading in its step. The 1 hour step gives fewer, wider columns, and the Δ chip changes with it. The newest column can be part-complete, so its change can cover less than a full step.
Chart Shows
- Whole session (default): from 9:15 to now.
- Last hour, Last 30 min, Last 15 min: the plane is built from the readings of that stretch only. A window longer than the session so far is greyed out.
- Custom: two clock selects, From and To, in 15-minute steps (From runs from 9:15 to 15:15, To from 9:30 to 15:30, then 15:40). To is always later than From.
Because the model is built from the chosen window, the oldest column of every window has no earlier reading and shows dashes (Step 11). Colours are re-measured for the window too, so the same tile can be deeper or paler than in the whole session.
Session Replay
Turn on Session replay and a strip opens above the plane. It steps through the columns of the plane, not minutes.
- Buttons: first reading, previous, play or pause, next. The slider seeks. Speed is 1x, 2x, 4x (columns a second). Latest returns to the newest. Escape closes the strip.
- While you replay, everything follows that reading: the columns drawn, the market line, the LTP columns, the Support, Resistance and Max Pain tags and the insight card's time. Changing the symbol, expiry, step, scale, strikes or window ends the replay.
Tiles, the strike column and the market line
The question How do I make a tile show more or less, and how many strikes are drawn?
| Setting | Choices | What it does |
|---|---|---|
| Tile size | Compact (default), Wide | Wide tiles are at least 104 pixels and show two lines, like the chain; about five columns a side on a 1440-pixel screen. Compact tiles are 46 pixels and fit more of the session. |
| Tile colour | Amount, Build-up (default) | Step 10 |
| Colour scale | Session, Each time, Each strike | Step 10 |
| Build-up in each tile | On (default) | The two-letter code in the tile |
| Change beside Open Interest | On (default) | The second figure. Reads Open Interest beside the change when Change leads |
| LTP in each tile | Off (default) | The contract's price at that time |
- Strikes: 11, 15, 21, 25 or 31, default 15, centred on the ATM strike of the newest reading. The hint line gives the range of strikes drawn and how far it reaches from the price, as a percent. Strike spacing differs between underlyings, so read the range, not the count.
- The strikes are fixed by the newest reading. If the market moves, rows do not change with it during the session.
- Keep Call & Put LTP fixed beside Strike (Both only), Support & resistance, Max pain and Put minus Call Open Interest switch the parts of the strike column described in Step 5.
The insight card, opened
The question What is the card measuring, and over which window?
Press View insight. The card reads the stored readings directly, not the tiles, sums Call and Put Open Interest over the strikes drawn, and compares the newest reading with one from the window's start.
| Part | What it says |
|---|---|
| Measured over | 5 min, 15 min or Day. The default is 15 min for an index and Day for a stock; the page remembers your choice. 5 min and 15 min need a stored reading about that far back (within about 1.5 and 2.5 minutes); otherwise the card says Not measured. |
| The build | The change since the previous close, calls and puts, with the figures it moved from and to. Day uses each leg's exchange previous-day Open Interest; a leg whose previous-day figure is missing is left out, and when the figures cover less than 90% of the Open Interest, or are missing, the card measures from the first reading of the session and says so. |
| The last 5 or 15 min | The shorter change and its verdict |
| The levels | Support and Resistance with their distance from price, the Put wall and Call wall (highest Put Open Interest at or below price and highest Call Open Interest at or above it, read within the 15 strikes around spot) and Max Pain |
| Caveat | Open Interest counts open positions, not who opened them; legs missing at one end are left out; a level that sits outside the strikes drawn; the tiles are step buckets while the card reads every reading |
A leg that is missing at one end of the window is left out of both sums, so a thin strike's whole standing book is never printed as a change. The panel says how many legs were left out.
The hover card: the two moves behind a tile
The question What exactly changed in this tile, in numbers?
Rest a mouse pointer on a tile for about 450 ms. The card opens. It is the option chain's Build card for one strike between two columns. It does not open on touch.
- Basis is the two column times it compares, for example 2:55 → 3:05.
- Premium: the percent change and the two prices. Open Interest: the signed change, the percent, and the exact contracts before and after; the second is the tile's own figure. Spot: the underlying's move over the same span.
- The last line is a mechanism, never a forecast: Fresh long positions are opening, Fresh short positions are opening, Short positions are closing, Long positions are closing. A tile with no pattern says which figure did not move.
Keyboard
Every tile is a button. Tab reaches one tile in each wing; the arrow keys move between tiles, Home and End jump to the first and last column, and Enter or Space selects a tile (a white ring marks it). The selected tile defaults to the ATM tile in the newest column.
Use it well
How do I read it without fooling myself, and what is a sensible routine?
A Worked Read, Start to Finish
The question Can I see the whole method on one page, with numbers?
All figures below are illustrative: one synthetic NIFTY session, frozen at 3:05 pm on 25 September 2026, expiry 29 September (4 days to expiry), the spot at 23124.83. The plane and card in the first figure show 15 strikes (22750 to 23450); the open card in Step 15 shows the 21-strike default, so its figures differ.
- The verdict. The card reads Bullish indications · puts added, calls cut. The chips say calls changed by −38.91L and puts by +1.96Cr since the previous close, and Puts minus Calls is +4.28L over 15 minutes. Two changes compared, nothing more.
- The size. On the plane the largest Open Interest is on the Put side near and below the money: the 23000 Put holds 1.47Cr. The largest Call tile is 1.01Cr, at 23400. In Amount colouring on the Session scale, every tile would be shaded against the largest tile on the plane, the 1.47Cr Put, whichever side it is on.
- The age. Read the 23000 Put row outwards from the strike column: 1.47Cr, 1.45Cr, 1.43Cr, 1.41Cr. It has grown across the last four columns, not appeared at once. The 23100 Put at the money is 1.14Cr but is being cut (LU, −78.7K) in the newest column.
- The tags. Support 23050, Resistance 23150, Max Pain 23250, and walls read within the 15 strikes around spot: the Put wall at 23000 (the largest Put Open Interest at or below spot) and the Call wall at 23400 (the largest Call Open Interest at or above it). The Put wall (23000) is not the Support tag (23050): they use different rules (Step 5, Step 15).
- The market line. Spot 23124.83 sits between a Low of 23060.10 and a High of 23135.88, near the top of the day's range. The ATM Straddle is ₹205.40, which the page converts to an expected move of ±174.59 (205.40 × 0.85), a band of 22950.24 to 23299.42 (spot 23124.83 ± 174.59). The 23000 Put wall and the 23150 Resistance tag are both inside that band; the 23400 Call wall is above it.
- The conclusion you are allowed. The largest tile on the plane is a Put, 1.47Cr at 23000, and that row has grown across the last four columns. The heatmap does not say who holds them, and it does not say price will stay above 23000.
The last step is the discipline of the whole guide: say what the picture shows, then stop.
One Dominant Strike, or a Broad Plateau
The question What does the shape of a column say about how positions are spread?
Read one column downward, from the top strike to the bottom. The shape, not any one number, is what the colour shows best.
| Shape | What you see | A careful reading |
|---|---|---|
| Peak | One deep tile with pale tiles either side | Open Interest is concentrated at one strike. Check its row: built recently, or there all session? |
| Plateau | Several neighbouring tiles of similar depth | Open Interest is spread over a band. No single strike dominates. |
| Split | Two deep regions with a pale gap | Two concentrations. They can be two positions, or one spread across two strikes. |
| Flat | Everything of a similar shade | Often a scale effect, for example one very large tile elsewhere: check the colour scale and try Each time. |
A peak on one side of the money and a plateau on the other is a description of the book. It does not say which will hold.
Traps That Make a Heatmap Mislead
The question What are the most common ways a reader is led wrong, and how do I avoid each?
Trap 1: Deep means "will hold"
A deep tile is a large number of open contracts. It does not mean a floor or a ceiling. Open Interest can be closed, rolled or hedged, and a tile in the newest column can be deep only because it was added in the last few minutes. Read the row before you read the tile.
Trap 2: Red and green as price direction
In Amount colouring red is Calls and green is Puts: the side, not a rise or fall. In the default Build-up colouring they name the move of the contract's own premium. Check the Tile colour setting in Customise before you read a colour.
Trap 3: Comparing shades across screens
Two heatmaps, two scales, two windows, two sets of strikes: shades are not comparable. Changing the strike count or the scale re-colours every tile.
Trap 4: Reading a change as a day's activity
A tile's change is the change since the column before, over the step shown in the chip. It is not the day's change. The day's change is in the insight card, on Day.
Trap 5: The verdict as a view on direction
Puts added and Calls added compare two changes. Put writers and Put buyers both add Put Open Interest, and the card cannot tell them apart. The build-up codes add the premium's move, but they do not say who is behind either.
Trap 6: A held tile or a dash read as activity
A held tile repeats an old reading. A dash means no earlier reading. Neither is a change.
Risk Notes
- Options can lose the whole premium. Open Interest says nothing about your own risk.
- The heatmap does not compute charges, taxes, margin or the cost of getting in and out.
- Near expiry, Open Interest at and around the money can change within a column, so a level seen earlier may no longer be there.
Two routines you can repeat
What order do I read in on expiry day, and when I hold a position for days?
Two Routines
The question What is a steady order of reading, so I do not skip a step?
Expiry Day
- Open the heatmap for the expiring contract. Check that the expiry capsule names the expiring contract.
- Keep the step at 15 min and set the strikes to 11, so the rows nearest the money fill the plane.
- Read the insight card on 5 min, then 15 min (the Measured over control). Is the verdict steady or flipping?
- Read the strikes nearest the money across the newest columns. Is Open Interest being added or closed there? Hover a tile if the code is not clear.
- Compare the market line with Day Low and High and the expected move band. Is price near an edge of the band?
- Keep Session replay for after the close, to review the day's build.
Positional
- Use 21 strikes, 15-minute columns and Whole session. Read the insight card on Day.
- Note the Support, Resistance and Max Pain tags and the Put wall and Call wall in the card, with their distance from price.
- Look at which side's deep tiles were built early and which this hour. Build-up colouring marks the tiles where positions were added.
- Repeat at the same time of day for a few days and compare your notes. The page shows only the latest day.
The States: When the Plane Is Thin or Empty
The question Nothing useful is showing. What is wrong, and what can I do?
| What you see | Why | What to do |
|---|---|---|
| No session history yet | No reading at all exists, not even the page's own fetch of the chain | Wait for the next reading, or choose another expiry |
| One column, dashes, Not measured | Only one reading exists, so no change can be computed | Wait for more readings; the insight card needs one about 5 or 15 minutes back |
| A dash in the oldest column | The oldest column of a window has no earlier reading | Normal; widen the window to see changes earlier |
| held | The strike was missing from a reading | Do not read it as activity |
| Fewer columns than expected | A short window, a large step, or the session just opened | Choose Whole session or a smaller step |
| Strikes missing at the edge | The file lists fewer strikes than the count chosen | Choose fewer strikes |
Two more messages can replace the plane. Building the heatmap, with Waiting for the first Open Interest snapshots, shows while the first readings are still arriving. Heatmap unavailable, followed by the reason, shows when the page cannot be built; the picture above shows the reason No historical snapshot data found for NIFTY. Wait, or choose another expiry from the capsule.
Using the Heatmap on a Phone
The question What changes on a small screen?
- At 900 pixels or less the plane moves in pages, one page of columns at a time. Dots under STRIKE show the page; with many pages a bar replaces them, as in the pictures.
- A tap selects a tile; a readout above the plane gives the strike, side, time, Open Interest, change and build-up in words. There is no hover card on touch.
- Tiles are narrower (about 72 pixels wide, 52 compact), so use Compact tiles and fewer strikes to see more.
- Customise is the settings button in the top bar.
Which tool, when
Which page answers which question?
Which Tool When
The question When should I use the heatmap, and when another page?
| Question | Use |
|---|---|
| Where is Open Interest large, and when did it arrive? | OI Heatmap |
| The exact figures for one strike, with the other columns | Option Chain (guide) |
| Open Interest by strike as bars, and the zones | Open Interest |
| Which strikes moved most in a window | OI Spurts |
| The Put-Call Ratio (Put Open Interest ÷ Call Open Interest) over time | PCR |
| Which contracts or underlyings stand out across the market | Options Scanner (guide) |
| The payoff of a position you are building | Strategy Builder (guide) |
Glossary
The question What does each word on the page mean?
- Open Interest
- The number of option contracts still open at a strike. Not the same as volume.
- Strike
- The price at which an option can be exercised. One row of the plane.
- ATM
- At the money: the strike nearest the spot price. The row carries an amber wash and the tag ATM.
- Spot
- The current price of the underlying, drawn in the capsule on the market line.
- Lakh, crore (L, Cr)
- The page prints Open Interest as K (thousand), L (lakh, 100000) and Cr (crore, 10000000) contracts.
- Build-up
- The name for what a contract's premium and Open Interest did together between two columns: Long Buildup, Short Buildup, Short Covering, Long Unwinding.
- Column
- One time step of the plane, showing the last reading in that step.
- Δ chip
- The label under the newest time: the step each change is measured over (5m, 15m, 30m, 1h).
- Held
- A tile that repeats a strike's last reading because the strike was missing from a reading.
- Colour scale
- What a tile is measured against: Session, Each time or Each strike.
- Support, Resistance
- Strikes where Put (Support) or Call (Resistance) Open Interest is concentrated, by the Open Interest page's zone rule. Descriptions of positions, not of price.
- Max Pain
- The strike with the lowest total payout to option buyers at expiry, over every strike of the expiry.
- Put wall, Call wall
- The highest Put Open Interest at or below the price, and the highest Call Open Interest at or above it, read within the 15 strikes around spot. Shown in the insight card.
- Straddle
- An ATM Call plus an ATM Put. The Straddle table adds the two sides at each strike.
- DTE
- Days to expiry, shown in the expiry capsule.
- Session replay
- A strip that steps the plane back through its columns.
Questions Readers Ask
The question Which short answers do readers look for most?
Does the heatmap show total Open Interest or the change?
Both. The capsule in the page bar chooses which one a tile leads with, and the second figure shows the other. In the default Build-up colouring, colour follows what the premium and Open Interest did; in Amount colouring it follows the size of the Open Interest.
What does a deep tile mean?
That many contracts are open at that strike, measured against a maximum chosen by the colour scale. It does not say who holds them or where price will go.
Why are some tiles dashes?
The oldest column of a window has no earlier reading, and a tile whose premium or Open Interest did not move has no clear pattern.
Why does the page say each wing but the scale is shared?
The Overview (the ⓘ button) says tiles compare depth within each wing. In the code the maximum is taken over Calls and Puts together. The Straddle table has its own. See What we have not verified.
How current is the data?
The stored readings are re-read about once a minute while the market is open and the page fetches the option chain about every 5 seconds, for the LTP columns and the market line. The tiles are not tick by tick.
Why is the newest column part-complete?
A column shows the last reading in its step. The newest one ends at the latest reading, which may be before the step is over.
Can I look at an earlier day?
Not on this page. It draws the latest trading day only.
What is the difference between Support and the Put wall?
Support is the Open Interest page's zone rule, snapped to a strike. The Put wall is simply the highest Put Open Interest at or below the price, read within the 15 strikes around spot. They can differ.
Does Build-up mean who is buying?
No. It names what the premium and Open Interest did together. Open Interest cannot say whether people were buying, writing or hedging.
What We Have Not Verified
The question Which statements could this guide not confirm from the source?
These are things a careful reader may want to check for themselves. Everything else in the guide was read from the page's source code, and the pictures are of the real page.
- Where the stored readings come from at their source, and how late they are there. Only the page's own re-read interval is known.
- Why the expected move is 0.85 times the ATM straddle. It is the option chain's convention, and no study is cited.
- The exact weights the Support and Resistance rule gives to strikes at each number of days to expiry. The rule is in the source; the reason for the weights is not documented.
- Whether the Overview's "within each wing" is intended. The code shares the colour maximum between Calls and Puts; the page text says each wing.
- Lot sizes, strike spacing, expiry weekdays and holidays. These are exchange facts that change over time; this guide does not state them (the NIFTY lot size of 65 is confirmed; other lot sizes are not).
- Whether the Open Interest figures the page prints count lots (contracts) or units (contracts times the lot size). The guide follows the page's own word, contracts.
- Whether the collector's row a minute holds at every moment of the session. A strike missing from a reading shows as a held tile, but why it is missing is not known.
- Whether a Custom window that was remembered reopens as Whole session, as other pages do. The setting is stored as Custom; the reopening rule was not confirmed for this page.
- The pictures are captures of the real page on illustrative data, and some use different strike counts (15, 21 or 11 strikes). Their figures agree within a picture, not always between pictures.
Sources
The question Where in the source was each part read?
Values are as of 15 October 2026. Paths are in the project's source. Each number the guide may need to change is in scripts/guides/oi-heatmap-parts/limits.mjs with its source line.
| Part | Files |
|---|---|
| Start, Page map, Steps 1 to 7 | OiHeatmapPage.tsx, HeatmapCustomizePanel.tsx, src/App.tsx (archive reads), src/api.ts (day files), src/lib/straddlePremium.ts |
| Part B | oiHeatmapModel.ts, openInterestModel.ts (classifyBuildUp), oi-heatmap.css, heatmapHover.ts, src/utils/formatters.ts, src/utils/marketVocabulary.ts |
| Part C | HeatmapCustomizePanel.tsx, heatmapSettings.ts, src/lib/chartWindow.ts, src/components/common/SessionReplay.tsx, heatmapInsight.ts, src/lib/insightWindow.ts |
| Part D | heatmapInsight.ts, src/lib/oiZones.ts, src/lib/maxPain.ts, the guide's own routines |
| Mock and pictures | scripts/guides/oi-heatmap-mock.cjs, scripts/guides/shot-oi-heatmap.cjs, public/oi-data/NIFTY/2026-09-25-close.json |
Related: Option Chain guide, Open Interest guide, PCR guide, Max Pain guide.
Test Your Knowledge
Check the mechanics before you take them to a live chain.
1. On the heatmap, what do the vertical axis, the horizontal axis and the depth of colour show?
2. In Amount colouring, which side of the Strike column do the Calls sit on, and in what colour?
3. In Amount colouring, a Put row is pale in the older columns and deep beside the Strike column. What does it show?
4. The oldest column of a window shows dashes for change. Why?
5. A Put tile reads LU. Which statement does the page support?
6. Two heatmaps each show a tile in their deepest shade. What can you say about their Open Interest?
7. A tile says held. What does that mean?
About the Sahi OI Heatmap
The OI Heatmap plots strikes down one axis and time across the other, shading each tile by Open Interest. It shows where Open Interest is concentrated and how it built up through the session.
It answers a question the chain cannot: not just which strikes are heavy now, but whether they were heavy all session or filled up in the last hour. Deep only in the newest column means recent; deep along the whole row means there since the morning.
At a glance
- Data
- Sahi market data for NSE and BSE options
- Updates
- Option chain re-fetched about every 5 seconds in market hours
- Coverage
- 217 NSE and BSE index and stock F&O underlyings
- Access
- Free — no login, no download
- Orders
- Analysis only. Sahi does not accept orders
See it on today's numbers
Everything above is method. These articles apply it to a live book — oi heatmap among the rest — and are rebuilt as the snapshot data refreshes. Where a symbol's option book is too thin to support a reading, the article says so rather than asserting a level.
Read next
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Option Chain
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Each guide pairs with a live tool. The options FAQ collects every question from all of them in one place.