Article
What Is an Expert Advisor (EA)? A Plain-English Guide
An Expert Advisor, or EA, is a program that runs inside the MetaTrader trading platform and follows a fixed set of trading rules for you. It watches prices, checks its conditions, and places, manages and closes trades without you clicking a button. The name comes from MetaQuotes, the company behind MetaTrader 4 and MetaTrader 5.
How an EA works
Every EA repeats the same simple cycle, many times a minute:
- Read the market: current prices, spreads and any indicators the rules depend on.
- Check the rules: for example, "buy when the trend is up and price pulls back to support".
- Act: send an order to the broker when the rules say so.
- Manage the trade: move a stop, take profit, or exit when conditions change.
EAs are written in MetaQuotes' own languages: MQL4 for MetaTrader 4 and MQL5 for MetaTrader 5. An EA only works while MetaTrader is open and connected, so many traders run it on a Virtual Private Server (VPS), a rented computer that stays online around the clock.
Why traders use them
- Discipline: an EA applies the same rules to every trade. It does not hesitate after a loss or get greedy after a win.
- Coverage: it can watch many currency pairs at once, through the night and across sessions.
- Speed: it reacts the moment its conditions are met.
- Testability: its rules can be run against years of past prices before any money is at risk.
What an EA cannot do
An EA is only as good as its rules, and honest vendors say so plainly.
- Markets change. Rules that worked in one period can stop working in another. Past results do not predict future ones.
- Over-fitted rules. A strategy tuned too closely to old data can look perfect in a test and fail live.
- Technical failures. A lost connection or a crashed computer can leave a trade unmanaged, which is why a VPS and hard stop-losses matter.
- Slippage and gaps. The price you get can differ from the price the EA asked for, especially in fast markets or over a weekend.
- Faster is not the same as profitable. Speed only helps if the underlying rules have a real edge.
How to tell a serious EA from a gimmick
Look for results tested on data the rules never saw, a live track record verified by a third party, clear stop-losses on every trade, and a seller who explains the risks as readily as the benefits. Be wary of grid or "martingale" systems that keep adding to losing trades, and of any promise of guaranteed or effortless profit.
How Bruno approaches this: every rule our EAs use must hold up on older data and on newer data it was never tuned on, and every trade carries a stop-loss.
Trading foreign exchange on margin carries a high level of risk and may not be suitable for all investors. You can lose more than your deposit. This content is educational and is not investment advice.
Sources: CMC Markets: What Is an Expert Advisor? · AvaTrade: Understanding Auto-Trading and EA Trading Systems