Thinkorswim — Free Professional Platform with thinkScript Backtesting

Thinkorswim (ToS) is Charles Schwab’s flagship trading platform (acquired from TD Ameritrade). It includes built-in strategy backtesting via thinkScript and an OnDemand feature that replays historical market data. Completely free — no platform fees, no data fees for US equities.

Language: thinkScript | Platform: Desktop, Web, Mobile | Price: Free

thinkScript

Proprietary domain-specific language with simplified Java/C-like syntax. Designed for custom studies, strategies, and scans.

def shortAvg = Average(close, 50);
def longAvg = Average(close, 200);

AddOrder(OrderType.BUY_TO_OPEN, shortAvg crosses above longAvg);
AddOrder(OrderType.SELL_TO_CLOSE, shortAvg crosses below longAvg);
  • Declarative style — define conditions, platform handles execution
  • Built-in functions for SMA, RSI, MACD, etc.
  • AddOrder() for generating buy/sell signals
  • Multi-timeframe and multi-instrument references
  • No loops or complex control flow (limited vs general-purpose languages)

Difficulty: Beginner-Intermediate — easy to start, but limited expressiveness for complex strategies.

Strategy Tester Features

  • Add strategy studies to chart — platform plots signals on historical data and generates performance report
  • OnDemand — replays historical market data in real-time
  • Paper trading built-in (no real money needed)
  • Performance report: P&L, total trades, win %, average trade, max drawdown, profit factor
  • Timeframes: 1-min to monthly
  • Daily data going back decades; intraday 180 days to ~3 years depending on timeframe

Limitations

  • Single-instrument only — no portfolio backtesting
  • No commission/slippage/spread modeling in backtests
  • No optimization engine or parameter sweeping
  • No walk-forward analysis or Monte Carlo simulation
  • Bar-level execution (not tick-level simulation)
  • Cannot export backtest results programmatically

Supported Instruments

  • US Stocks and ETFs
  • Options (single legs and spreads)
  • Futures and futures options
  • Forex (70+ pairs)
  • Crypto (via futures)

Pricing

Completely free. Requires a Charles Schwab brokerage account (no minimum balance). Real-time US equity/options data included. Futures and forex data free with approved accounts. Paper trading available without funding.

Pros

  • Completely free platform with professional-grade charting
  • Easy scripting language — low barrier to entry
  • Massive community with thousands of shared scripts
  • Excellent for quick strategy validation and visual signal checking
  • Paper trading and OnDemand replay included
  • Real-time data at no cost
  • Options analytics among the best available

Cons

  • Backtester is simplistic — no tick-level simulation
  • No portfolio backtesting
  • No commission/slippage modeling in backtests
  • No optimization or parameter sweeping
  • thinkScript is not portable to other platforms
  • Limited historical intraday data depth
  • Cannot export results programmatically
  • No walk-forward analysis
  • Platform occasionally slow with complex studies

Who Should Use Thinkorswim?

Thinkorswim is the best free option for US equity and options traders who want quick strategy validation without paying for software. The thinkScript community provides thousands of ready-made scripts. OnDemand replay is useful for reviewing past market behavior.

For serious backtesting with optimization, use AmiBroker, MultiCharts, or TradeStation. For free backtesting with better optimization, try MetaTrader 5. For Python flexibility, see Backtrader or Backtesting.py.

Resources