Broker emulator · Flowscope Script

When and at what price simulated orders fill, and how commission, slippage, funding and margin are applied.

The broker emulator turns order calls into fills. It follows TradingView’s strategy emulator and is deterministic: the same script on the same bars always produces the same trades.

The basic cycle

For every confirmed chart bar, in this order:

Fill phase. The emulator walks the bar along its price path and fills pending orders: market orders at the open, then limit, stop and exit orders where the path reaches them.
Script phase. on chart.close runs and sees the account after this bar’s fills. It may place, modify or cancel orders.

Orders placed in the script phase of bar N are first worked in the fill phase of bar N + 1; market orders fill at its open plus slippage.

Timeline example

A 1-hour chart with slippage: 1, tick size 0.1, a long entry with a 300-tick stop:

Bar	Open	High	Low	Close	What happens
10:00	61,950.0	62,120.0	61,900.0	62,080.0	`on chart.close`: the EMAs cross up. `strategy.entry("Long", strategy.long)` and `strategy.exit("SL", "Long", loss: 300.0)` are queued.
11:00	62,075.0	62,300.0	62,050.0	62,250.0	The market buy fills at 62,075.0 + 0.1 = 62,075.1. The stop is armed at 62,075.1 − 30.0 = 62,045.1; the low of 62,050.0 stays above it.
12:00	62,240.0	62,260.0	61,980.0	62,010.0	Path: open → high → low → close. On the way down the stop triggers and fills at 62,045.1 − 0.1 = 62,045.0.

Exits are live from the moment the entry fills, including the rest of the entry bar: had the 11:00 low been 62,040.0, the stop would have filled on the entry bar.

processOrdersOnClose

With processOrdersOnClose: true, orders placed in on chart.close are worked at that bar’s close instead of the next open: market orders fill at the close plus slippage.

Setting	Signal at bar N’s close fills at
`false` (default)	Open of bar N + 1
`true`	Close of bar N

On liquid 24/7 crypto markets the next open is usually within a tick of the close, so the difference is small, but around news it is not.

A bar reports four prices. The emulator assumes the path open → nearer extreme → farther extreme → close: when the high is at least as close to the open as the low, price goes up first, otherwise down first. Orders are checked along each segment in the order the path reaches them, so for a bracket the leg on the first segment wins.

useBarMagnifier would walk lower-timeframe bars inside each bar instead. Charts do not provide them yet, so strategies on charts always use the four-point path.

Limit orders

A limit order fills when price reaches the limit: a buy limit at 3,000.0 fills when the path touches 3,000.0. It fills at the limit price, or at the open when the bar opens beyond it (a better price). Limits never slip.

backtestFillLimitsAssumption: n asks for more: price must trade n ticks through the limit before it fills, at the limit price. This approximates waiting in the queue behind other orders.

Stop orders and gaps

A stop triggers when price trades at or beyond it and fills at the stop price plus slippage. When a bar opens beyond the stop (a gap), it fills at the open plus slippage, worse than the stop.

Slippage and commission

Fill	Slippage	Commission
Market	`slippage` ticks against you	Yes
Stop, stop-loss, trailing stop	`slippage` ticks against you	Yes
Limit, take-profit	None	Yes
Margin call	None	Yes

Commission follows commissionType and commissionValue and is part of each trade’s profit.

Funding on perpetuals

With fundingCosts: true (the default), a position held through a funding settlement pays or receives rate × position value at the open of the first bar at or after the settlement: longs pay a positive rate and shorts receive it. The rates are the ones the data hub recorded just before each settlement; aggregated markets use the open-interest weighted rate of their venues. Funding is part of each trade’s profit and of the Strategy Tester’s Funding paid.

Margin and liquidation

With marginLong or marginShort below 100 % (or leverage above 1), positions may be worth more than equity. An entry the account cannot fund is skipped. On every price the emulator checks that equity covers the margin of the position; when it no longer does, it liquidates part of the position, as TradingView does: four times the contracts needed to cover the shortfall, at that price. Each event is a Margin call fill and counts in the tester’s margin calls. strategy.marginLiquidationPrice tells where the next one would start.

Aggregated markets

On an aggregated market the emulator fills at the aggregated price, which no single venue offers. Treat such a backtest as a view of the market as a whole and confirm promising results on the venue you would trade.

Repainting and look-ahead

A strategy only sees the past: on chart.close runs after a bar is confirmed, and its orders fill on later prices. Two things still deserve care:

Signals from on chart.update use the forming bar, whose values change until it closes. Place orders in on chart.close.
Reading another timeframe’s forming values gives the developing bar, not a confirmed one. See repainting.