Trading bots · Expert advisors

What is an expert advisor, and what happens when it runs

An expert advisor is a program attached to a chart in a trading platform that trades that account on rules written in advance, with nobody pressing the button. It does not analyse anything in the way a person does, and it decides nothing its rules do not cover: it reacts to notifications the terminal sends it and, when the rules say so, submits an order.

Almost everything written about EAs is written from the marketing side. This page is written from the platform maker's own documentation: what happens the moment a new price arrives, how it differs from an indicator, what has to stay switched on for it to work, what it is not despite the word "advisor", and what you are actually buying when you buy one ready-made.

Sources read on 31 August 2026 · linked at the foot of the page

This page does not describe the Fondeobot software

What an expert advisor is, and where the name comes from

A program that runs rules against an account. The name comes from a platform, not from a profession.

It is an executable file that gets compiled, dragged onto a chart and left there handling events. While it is attached it can open and close positions, place and remove pending orders and modify the ones it already has, all inside the account it is loaded in. To make it stop, it has to be removed from the chart: the MetaQuotes documentation says exactly that, and adds that expert advisors work until they are explicitly removed, with information about what is attached saved between terminal sessions.

The term is not generic. It comes from MetaTrader, the MetaQuotes platform, where "expert advisor" is one of the program types you can write in its language. Outside that, the same thing is called a bot, a robot or an algorithm. It is said here because a definition that hides where the word comes from is an incomplete definition, and because the sources for this page are that maker's documentation: citing it while hiding whose it is would be worse. What this page describes is that category of program, not the software sold on this site.

One installation detail clears up a lot: a single chart takes at most one expert advisor and one script, while it takes as many indicators as you like. If somebody tells you they have three EAs running on one chart, either they are something else or they are on different charts.

What happens the moment a new price arrives

The program does not watch the market: it waits for the terminal to tell it. And if it is busy, that message is lost.

The terminal raises an event for every new quote and hands it to the expert advisor, which handles it through a function reserved for that. That is the whole mechanism: no event, no execution. An EA sitting still is not an EA that decided not to trade, it is an EA that was sent nothing.

Which produces the limit nobody mentions. The documentation is explicit: "In case when OnTick function for the previous quote is being processed when a new quote is received, the new quote will be ignored" — the event is never queued. Quotes arriving while the program is working are dropped until it finishes, and the function only starts again on the next quote received. In a quiet market you will not notice. In a fast stretch, or with slow logic, the program can end up never seeing prices the market traded through, and no backtest reproduces that.

It restarts more often than you would think
The initialisation event does not only fire when you load it. It is generated again when the chart's instrument or timeframe changes, when the program is recompiled, when its input parameters are changed from the settings window and — the one that surprises people — when the account is changed. Any of those four returns the program to its initial state.
Closing the terminal says goodbye, and in a hurry
Before unloading the program the terminal sends it a deinitialisation event, which is also generated when the terminal closes, when the chart closes and right before the instrument or period changes. The function handling it gets 2.5 seconds: if it has not finished by then it is forcibly terminated. A shutdown is not a guaranteed orderly stop.
Startup comes with a wait, and it can fall short
Before it begins, an expert advisor needs an up-to-date trading environment, access to the history for its symbol and period, and data synchronised between terminal and server. The terminal grants it a start delay of no more than 5 seconds for all of that, after which it starts with whatever data is available. With no connection to the server, that start is delayed.
The automated trading button does not switch it off
Prohibiting automated trading only means the expert advisor is not allowed to send trade requests; the program keeps working and keeps receiving quote events. It does not stop an execution already under way either. It is an outbound filter rather than a switch, and the distinction tends to be discovered late.

Expert advisor, indicator and script: three different things

All three are written in the same language and installed the same way. Only one can send an order.

They get confused because they share a language, an extension and an installation route, and because in a screenshot they look alike. The documentation separates them by the only thing that matters here: what each one can do with the account.

Program typeWhat it can do

Expert advisorTrades

When it runs: On every event, until it is removed
What it does to the account: Opens, closes and modifies orders
How many per chart: One

ScriptRuns once

When it runs: Once, then unloads itself
What it does to the account: One sequence of actions, then ends
How many per chart: One

They do not start again when the terminal restarts, because no information about them is saved.

IndicatorNo trading

When it runs: On any change in the price data
What it does to the account: Nothing: it calculates and draws
How many per chart: As many as you like

Every indicator on one symbol shares a single execution thread, so one that hangs stops all the others.

The distinction is practical rather than academic: if what you are being shown on the chart is a line following the price, that has never traded anything. An indicator can be excellent and still say nothing whatsoever about results, because it produces none.

What an expert advisor needs before it can trade

A terminal switched on and connected. This is not a cloud service: it is a process running on a computer.

An expert advisor lives inside the terminal, and the documentation describes the consequence rather than the principle: when the client terminal shuts down, the program is sent its deinitialisation event and unloaded. There is no version of this that runs on its own somewhere. It is a program inside another program, and when the outer one closes, the inner one goes with it.

That, and nothing else, is why everybody in this market talks about servers. A home computer sleeps, updates, restarts and drops its connection, and each of those is a stop. So the operational question to ask somebody selling you an EA is not where the program is hosted, but who takes responsibility for the machine staying on and connected, and what happens when it is not.

The connection is not only there for trading, either. Without it the start is delayed by data synchronisation, and orders the program has already sent do not live in the terminal: they live on the broker's server, which is what executes them and what raises the event back when a trade operation is completed. Closing the terminal leaves the program unable to manage anything; it does not leave the account empty.

What an expert advisor is not

It does not advise, it guarantees nothing, and it is not exempt from the rules of the account it runs in.

It is not advice, whatever the word ‘advisor’ suggests
Investment advice has a legal definition in European law: "the provision of personal recommendations to a client, either upon its request or at the initiative of the investment firm, in respect of one or more transactions relating to financial instruments". An expert advisor recommends nothing: it sends orders in the account it is attached to. And the person selling you the program is not advising you by the act of selling it either. The word is a product label from one platform, not a description of a regulated activity.
It fits the definition of algorithmic trading, but not the obligations
The directive defines algorithmic trading as trading "where a computer algorithm automatically determines individual parameters of orders such as whether to initiate the order, the timing, price or quantity of the order or how to manage the order after its submission, with limited or no human intervention", and excludes systems used only to route orders without determining any trading parameter. An EA fits that squarely. What does not fit is the addressee: the obligations the rules hang off that definition fall on investment firms, not on the holder of an account. Knowing this heads off both opposite mistakes — thinking an EA is regulated, and thinking the rules have nothing to say about it.
It is not an exception to the rules of the account it runs in
If the expert advisor trades a funded account, the firm's rulebook applies to it exactly as it would to a person, with the aggravating detail that a program has no idea it is breaching anything. The full breakdown of the limits, with the figures and the official source for each, is on the page about FTMO and expert advisors, and it is not repeated here so the same figures do not live in two places.
It is not proof of anything, not even when it arrives with a curve
A well-built program says nothing about whether its strategy works, and an excellent backtest says little more. Why it says little, with the formal proof, is in the guide on whether trading bots are reliable; and how you check one particular record, step by step, is in how to verify a track record. Both are different questions from this one, which is why they live on different pages.

What you buy when you buy an expert advisor ready-made

A personal-use licence with a number of installations. Not the program, and almost never the code.

It is worth reading where it is written down, because "buy" suggests more than what arrives. The rules of the MQL5 Market, which is where most EAs are sold, put it plainly: "Purchasing a Product does not mean buying rights to it. The Product is transferred to the Buyer for personal use only." It cannot be resold, it cannot be decompiled — the attempt counts as a breach whatever the outcome — and it can only be installed the number of times the product declares.

In exchange the buyer gets two concrete rights, both with a deadline: to require a critical error to be fixed where it makes the product stop working, and to require the product to be brought into line with its stated functionality if it falls short. Both claims expire one month after the purchase. That is not much, but it is more than most direct sales offer, where no rules are published at all.

And there is a yardstick almost nobody uses, because it is buried in a European regulation. Investment firms trading with algorithms are required, before putting one into production, to have clearly delineated methodologies for developing and testing it, to have the deployment authorised by a person designated by senior management, and to ensure through those methodologies that the algorithm "does not behave in an unintended manner", keeps working effectively in stressed market conditions and allows itself to be switched off. One article further on they must be able to cancel immediately, as an emergency measure, any or all of their unexecuted orders: the so-called kill functionality.

None of that binds whoever is selling you an EA, and saying so matters: you are not catching a breach. What you have is the list of questions a professional has already had to answer. How it was tested before it was sold, who decides when it gets switched off, what it does in a broken market and how it is stopped dead are four free questions, and they apply to the system sold on this site exactly as they apply to any other.

Sources · read on 31 August 2026

Frequently asked questions

What is an expert advisor, and how is it different from a bot?

An expert advisor is a program attached to a chart in a trading platform that trades the account on rules written in advance, with nobody pressing the button. "Bot" and "robot" are the everyday words for the same thing; "expert advisor" is the technical name MetaQuotes gave it in the documentation for its platform, where it sits alongside other program types that do not trade at all. The difference is vocabulary, not quality or technology, and it is worth knowing because the label a seller picks tells you nothing about what is inside.

Does an expert advisor advise me or recommend trades?

No, whatever the name suggests. An expert advisor issues no recommendations: it sends orders in the account it is attached to. Investment advice has a legal definition in European law — the provision of personal recommendations to a client in respect of one or more transactions relating to financial instruments — and it is an activity reserved to authorised firms. A program that trades on its own does not fit that, and neither does the person who sold it to you by the act of selling it.

Is an expert advisor the same thing as an indicator or a script?

No, and the MetaQuotes documentation separates them by what each one is able to do. The expert advisor stays attached to the chart, handles events and can send orders. The indicator draws: it calculates and plots, and does not trade. The script runs once and unloads itself when it finishes. On top of that, one chart takes a maximum of one expert advisor and one script, while indicators are unlimited. If somebody shows you "their EA" and what you are looking at is a line drawn over the price, what you are being shown is an indicator.

Can an expert advisor miss a market move?

Yes, and the platform maker documents it. The program does not watch the market: it waits for the terminal to send it a new-quote event. If a quote arrives while it is still processing the previous one, that event is not placed in the queue and is dropped. In a quiet market you will not notice; in a fast stretch, or with logic that takes a while on each pass, the program can end up never seeing prices the market traded through. It is a design limit rather than a fault, and no backtest reproduces it.

If I switch off automated trading, does the expert advisor stop?

Not entirely, and the difference matters. The MetaQuotes documentation is explicit: prohibiting automated trading only means the expert advisor is not allowed to send trade requests, while the expert advisor keeps working and keeps receiving quote events. It does not stop an execution already under way either. To make an expert advisor genuinely stop, it has to be removed from the chart. A button that looks like an off switch and is really an outbound filter is the sort of detail people find out late.

What rights do I get over an expert advisor I buy ready-made?

Fewer than the word "buy" suggests. The rules of the MQL5 marketplace, for one, say that purchasing a product does not mean buying rights to it: it is transferred for personal use only, it cannot be resold, it cannot be decompiled, and it can only be installed the number of times the product declares. In exchange, the buyer can require a critical error to be fixed, or the product to be brought into line with its stated functionality, provided the request is made within one month of the purchase. Read those conditions wherever they are written before you pay, because they vary from seller to seller.

Before you automate, compatibility

An expert advisor is not a strategy: it is a way of executing one. What sits behind the one installed here — how many strategies there are and how they coexist in one account — is described separately.

See the trading system

Continue reading

Three more guides on this, or on what sits next to it.