What is an arbitrage scanner and how does it work
An arbitrage scanner compares the price of the same instrument across exchanges in real time and finds the gaps that stay profitable after every cost. Here is what it has to account for, how a futures scanner differs from a spot one, and what Selltix does.
What an arbitrage scanner is
An arbitrage scanner is software that watches prices on many exchanges at once, compares the quotes of one instrument and shows opportunities with a positive difference: where it can be bought cheaper than it can be sold on another venue at the same time. Unlike a price aggregator that shows each exchange's "last price", a professional scanner computes what a trader actually gets - the spread between the buy price (ask) on one exchange and the sell price (bid) on the other, minus every fee.
How it works
- Collecting quotes. The scanner connects to the exchanges' data streams (WebSocket) and gets the best bid and ask of every instrument within a fraction of a second. Selltix runs its own connections to 26 exchanges and normalizes them into one model.
- Matching instruments. Exchanges name the same contract differently (BTCUSDT, BTC-USDT-SWAP, BTC_USDT) and use different contract sizes and price steps. The scanner brings them to one form, or the comparison is wrong.
- Computing the net spread. For every exchange pair it computes what buying at the ask on one and selling at the bid on the other gives after both sides' fees.
- Filtering. Stale quotes, thin books, instruments with a too coarse price step and short spikes that cannot be taken are dropped.
- Signal and execution. When the net spread is above the entry threshold, a signal appears. Selltix can open both legs on your accounts right away and close them when the prices converge.
What a good scanner must account for
- Both exchanges' trading fees - taker or maker, at your account's rate rather than the standard schedule. The fee is paid four times: entry and exit on each of the two exchanges.
- Bid and ask, not the last price. You can only buy at the ask and sell at the bid.
- Book depth. The best price may cover a few dollars. What matters is the average fill price (VWAP) for your size and the slippage.
- Quote freshness. A price a few seconds old may be gone. A spread on a frozen quote is a common false signal.
- Price step and minimum lot. If the price step is comparable to the spread, execution eats it; if the minimum order is larger than your size, the trade cannot be opened.
- Funding rates. On perpetual futures one side pays the other every 1, 4 or 8 hours. Funding can add to the result or take from it.
- How long the gap lives and the exit price. The result is the net at entry minus the cost of closing at exit. A good scanner shows both.
Why futures, not spot
Classic spot arbitrage - buy a coin on one exchange, transfer it, sell on another - needs withdrawals: network fees, withdrawal fees and minutes or hours of confirmations, while the spread disappears.
Selltix works with perpetual futures: a long on the cheaper exchange and a short of the same size on the pricier one, at once. No coins move between exchanges, there are no withdrawal or network fees, and the position as a whole does not depend on the market's direction - one leg's gain offsets the other's loss. When prices converge, both legs close and the difference is the result.
What makes Selltix different
- 26 exchanges, 3 of them decentralized (Hyperliquid, Aster, Lighter). On almost all of them (all but Lighter) the bot trades with its own trading client, no third-party libraries.
- Your account's fees. The net spread uses the real maker/taker rates the bot reads from the exchange with your keys.
- Book depth for your size. Every active signal shows the net your trade size would get on both real books, and each leg's slippage.
- Signal filters. Separate entry and exit thresholds (hysteresis), a per-coin pause after a stop, dropping stale quotes and too coarse price steps, a book depth check before entry.
- Execution, not just a scanner. Both legs open at once, real positions are checked against the exchange, with a stop loss, a holding time limit, funding modes and a smoke test before trading.
- Simulation and backtest. The simulation follows live trading's rules and shows which trades the bot would take with real money; the backtest picks thresholds on recorded ticks.
Risks
Arbitrage lowers the dependence on market direction but does not remove risk: the spread may not converge within the holding time, one leg may fail to fill, an exchange may delay an order or change its terms, funding may go against the position, and a sharp move can threaten one leg's isolated margin. Selltix gives no investment advice and guarantees no profit: you trade yourself, on your own accounts and at your own risk.
FAQ
Do I send money to Selltix?
No. Funds stay on your exchange accounts. Selltix uses API keys that can trade and cannot withdraw, stored encrypted.
Can I try it without real money?
Yes. The simulation runs the same trades on a demo balance, and the spread monitor is open without sign-up.
Why isn't the scanner's spread my profit?
Because the result is the net at entry minus the closing cost at exit, with fees, slippage and funding in between. The signal chart in Selltix shows both lines: net and close.
Which exchanges are supported?
26 USDT perpetual futures exchanges, listed on the main page.
Can I connect my own program?
A public API and an MCP server for AI assistants are in development and will come with the paid plans.