NinjaTrader Playback vs Sim101: what each test actually measures

Separate the data connection from the account

The connection supplies prices; the account selection determines where orders go. In NinjaTrader order-entry windows, choosing Sim101 sends orders to the simulator. Check that account field in each window rather than assuming one window changes every other window.

Prepare a replay session

1. Save and close live workspaces, then use a dedicated Playback workspace so replay activity does not affect their drawing objects.
2. For a Market Replay download, disconnect Playback and disable Enable market recording for playback in Options > Market Data. Open Tools > Historical Data, expand Get Market Replay data, and select the instrument and date. Keep the window open until the download finishes.
3. Choose Connections > Playback Connection. Select Market Replay or Historical to match your available data, set the date range, and start playback.
4. Use Show Available Data from the controller’s right-click menu to check instrument coverage. For a chart-based strategy, load bars before the replay start time so its calculations have earlier data.

Why replay and Sim101 fills can differ

Market Replay retains the recorded sequence of Level I and Level II events. Historical-tick playback has no market depth, and its detail depends on the provider. A test that needs depth cannot obtain it simply by switching the controller to Historical.

Playback101 processes orders immediately and synchronously, without the simulated internet delay used by Sim101. The Sim101 fill engine considers bid/ask volume, trade volume, queue timing and random delays between order states. Matching the visible prices does not make the execution models identical.

NinjaTrader also documents that session-end order expiration and cancellation through TimeInForce logic are unsupported on both accounts. Use these simulations for the behavior they model; they do not verify broker-side expiration.

Save results before rewinding or disconnecting

Disconnecting Playback resets its trade history. Moving the slider during playback also resets that history. Save the results you need before either action; changing the replay period is not just a different view of the same completed run.

Playback101 copies account properties such as commissions and risk settings from Sim101 when connecting. Reconnecting rebuilds those properties from the current Sim101 settings; they cannot be reset while Playback is connected.

Playback and Tick Replay are different features

Tick Replay controls historical event processing for indicators and strategies explicitly written to use it. It consumes additional resources and is not intended to reproduce live strategy order fills in a backtest. Enabling it does not turn a chart into a Playback session.

Testing a recorded period also leaves a separate operational question: what happens after a real connection loss or platform restart? Test recovery separately from replaying the trading logic.