Most gamma exposure tools draw the same three words on a chart: call wall, put wall, zero gamma. The words match from one tool to the next; the numbers behind them often do not, because each tool answers a handful of design questions differently, and usually without saying so. This page lists those questions. It names no product until the last section — the questions are the part worth keeping, whichever tool you end up using.
1. Which chain: the index or the ETF?
SPX and NDX options are cash-settled, European-style index options, and they are the book that hedging in ES and NQ relates to. SPY and QQQ options are ETF options: American-style, settled in shares, on a one-point strike grid, with their own holders and their own liquidity pockets. A level computed on SPY and rescaled to ES is a reading of a related book, not of the same one. Neither is wrong — they answer different questions. Ask which chain each level comes from, and whether the chart says so.
2. Which expiries: 0DTE only, or the whole chain?
SPX, NDX, SPY and QQQ list an expiry every trading day, and a large share of the day’s index option volume is in contracts that expire that afternoon. Near the money their gamma is far larger than a monthly contract’s, which is why intraday levels are usually built from the 0DTE slice. A whole-chain profile blends contracts that vanish tonight with contracts that will still be hedged next month: useful for the week’s structure, less so for the next hour. Ask which one a level is built from, and whether you can see the split by expiry.
3. Open interest, or today’s volume?
Open interest is published once a day, before the open: the standing book, what was held overnight. Today’s volume is what traded since the bell — it sees the new same-day positions that open interest cannot, but it does not know whether a trade opened or closed a position. A level built on open interest alone cannot change during the session; a level built on volume alone changes all the time. Ask which book each level comes from. A tool that shows both side by side lets you read their disagreement, which is information in itself.
4. How often does it refresh?
A level computed at 09:00 from yesterday’s open interest and a level recomputed every few seconds from the live chain are different objects that happen to share a name. Ask for the actual cadence — seconds, minutes or once a day — and whether the page you are looking at is the live feed or a delayed copy of it. A free page refreshed every 15 minutes can be perfectly honest, as long as it says so.
5. How does a level reach your futures chart?
SPX levels are in index points. ES trades at a different price: the basis, which moves through the session and jumps at each quarterly roll. An SPX strike printed as an ES price is off by the whole basis — tens of ES points early in a contract, depending on rates and dividends. Ask whether the levels are converted, with which basis, and how often that basis is read.
6. Where are the levels drawn?
A level read in another browser tab and copied by hand onto a chart is a level read late, and now and then copied wrong. Ask whether the tool draws on the platform you actually trade from or only on its own web chart, and whether the lines on your platform update by themselves when the levels move.
7. Can you check a level after the fact?
Every level looks convincing on the screenshot that was picked to show it. The way to judge one is to go back to sessions nobody picked: replay the day minute by minute, with each level where it was at that minute — not where it ended up. Ask how far back the history goes, and whether it keeps the level’s trail through the session or only its final value. A level redrawn with hindsight always looks better than it did at the time.
8. Does it say how it computes?
Every GEX figure rests on an assumption nobody can observe: which side of each contract the dealers are on. Ask for the sign convention, the books used, the cadence and the limits, in writing. A tool that publishes its method lets you decide how much weight its numbers deserve; one that does not leaves you to guess.
The checklist
- Chain: index (SPX, NDX) or ETF (SPY, QQQ) — and is it labelled?
- Expiries: 0DTE, or the whole chain — and can you see the split?
- Book: open interest, today’s volume, or both side by side?
- Refresh: seconds, minutes, or once a day — live or delayed?
- Futures: converted with a basis, and how often is it read?
- Platform: drawn where you trade, or on another tab?
- History: can you replay a past session with the levels as they were?
- Method: published, with its assumptions and limits?
How GammaTape answers them
- Chain: SPX and NDX for ES and NQ; SPY and QQQ for the ETF books — each level computed from its own chain.
- Expiries: the levels come from the 0DTE chain; the Overview splits net GEX by expiry.
- Book: open interest and today’s volume, side by side on Pro and Max; Starter carries the open-interest book.
- Refresh: the levels are recomputed every 3 seconds during the session; the public levels pages every 15 minutes.
- Futures: the MotiveWave extension measures the basis minute by minute from your own ES or NQ chart; the web desk switches to futures points with a basis you set or a suggested one; the public pages publish index points.
- Platform: the web desk, and MotiveWave on the Max plan. No NinjaTrader indicator is available yet.
- History: 30-day replay on Starter, 90 days on Pro and Max, each level with its trail as it was at the time.
- Method: written up on the methodology page → /methodology
Related
- Today’s SPX gamma levels, no account → /spx-gamma-levels
- Every term on this page, defined → /glossary
- Volume GEX vs open interest GEX → /blog/volume-gex-vs-oi-gex
- SPX to ES and NDX to NQ, the basis explained → /blog/spx-to-es-ndx-to-nq-basis-explained