Trading bots: what they do, and the four things they cannot do

What a trading bot is

A trading bot is a program connected to a market feed and a trading account, which evaluates conditions continuously and acts when its rules are met. Every one of them, however sophisticated, is doing the same three things: reading data, deciding, and sending an order.

What varies is where the decision comes from. A rule-based bot uses conditions a human wrote. "if the 50-period average crosses the 200 and RSI is below 60, buy". A statistical or machine-learning system infers its conditions from historical data. A copier has no logic at all and simply mirrors another account's trades.

The commercial reality worth knowing: in forex, "trading bot", "forex robot", "EA" and "automated trading system" are used interchangeably, and the interchangeability is mostly marketing. Under all of them sits a MetaTrader Expert Advisor or something functionally identical.

The main types, and what each is for

What an automated system cannot do

Four limits are structural rather than a matter of build quality, and understanding them is most of what separates people who use automation well from people who lose money to it.

It cannot know what it has not been shown. A rule set encodes past relationships. When the regime changes (a trending market turns to chop, a correlation that held for two years breaks) the system keeps applying yesterday's logic with full confidence and no awareness that anything has changed.

Backtests overstate almost everything. A backtest with clean fills, fixed spread and no slippage is not a simulation of trading, it is a simulation of arithmetic. Add realistic spread, variable execution and the requeues that happen in fast markets, and a strategy that looked excellent frequently becomes marginal.

Optimisation finds coincidences. Tune enough parameters against enough history and you will find a setting that fits it perfectly. That setting describes the noise in that particular sample, not a property of the market, and it stops working the moment it meets data it was not fitted to. This is curve-fitting, and it is the single most common reason a purchased system fails.

Recovery logic hides risk instead of removing it. Martingale and grid systems produce beautiful equity curves for months, because doubling into a losing position converts many small losses into rare enormous ones. The curve is not evidence of an edge; it is evidence that the loss has not arrived yet.

Evaluating a bot before you run it

Six questions, in the order that eliminates fastest:

1. What is the actual strategy? If the seller will not describe the logic in a sentence, there is usually nothing to describe.
2. Does it add to losing positions? Grid and martingale mechanics should be disclosed. If they are not disclosed, assume they are present and look at the drawdown.
3. What is the maximum drawdown, and over what period? A result with no drawdown figure is not a result. Run it through the drawdown calculator to see what recovering from it would take.
4. Is there forward-tested or live performance? Backtests are a filter, not evidence. Only out-of-sample results tell you anything.
5. How many parameters does it have? More knobs means more curve-fitting surface. A system with thirty optimisable inputs has almost certainly been fitted to its test data.
6. What happens in a gap? Weekend gaps and news spikes jump straight through stops. A bot with no answer to that has not been tested against reality.

And a rule that applies regardless of the answers: demo first, then the smallest live size your broker permits, for at least a month. A bot that behaves differently live than on demo is telling you something important about execution that no backtest could.

The MarketPro Expert Advisor

MarketPro is building an Expert Advisor for MetaTrader 4 and MetaTrader 5. It is not available to download yet, and this page will say so until it is.

What is open today is the waiting list. Install the app, open the EA tab, and join it; everyone on the list is emailed when the builds go live. There is no charge and no card involved in joining.

When it does ship, three things will be true about it by design:

• You install and run it. It executes on your terminal, on your account, under your configuration. MarketPro never touches your account and exercises no discretion over your funds.
• It ships with a kill switch and an explicit as-is licence with no performance guarantee.
• Availability is limited by region. Distribution is restricted, and eligibility is determined by residence rather than by a checkbox on a page.

Meanwhile the thing that is live is the signal feed: vetted trade ideas with entry, stop and three targets that you place yourself. That is the manual equivalent of what the EA will automate, and it is available today with one free signal a day.