What is an Expert Advisor (EA)?

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An EA only runs while its MetaTrader terminal is open and connected, so most users keep the terminal on a Windows VPS to keep it active around the clock. EAs cover a wide range of jobs: full strategies that generate their own entries and exits, trade managers that adjust stops or take profit, and copier EAs that mirror trades from one MetaTrader account to another. They are specific to MetaTrader; the cTrader platform uses cBots written in C# instead of EAs.

An expert advisor is an automated program, written in MetaTrader's MQL4 or MQL5 language, that runs inside an MT4 or MT5 terminal and trades or manages trades according to rules in its code. Once compiled and attached to a chart, it reacts to incoming price data and can place, modify and close orders without manual clicks.

Because it follows fixed logic, an EA does exactly what it is programmed to do, no more and no less. Traders use them to remove the manual step from a strategy, to enforce discipline around entries and exits, or to mirror trades from another account.

An EA works by running as compiled MQL code attached to a single chart inside the MetaTrader terminal. The terminal feeds it new ticks and bars, and on each event the EA's logic decides whether to open, change or close a position, then sends those orders to the broker through the terminal's connection.

This design means the EA is tied to the terminal. It only acts while MetaTrader is open, logged in and connected to the broker; if the terminal closes, loses connection or the machine sleeps, the EA stops and any rules it was enforcing pause until the terminal is running again.

• Written in MQL4 for MetaTrader 4 or MQL5 for MetaTrader 5, then compiled to an .ex4 or .ex5 file
• Attached to one chart and driven by that symbol's tick and bar events
• Sends orders to the broker through the terminal, not directly over the internet
• Runs only while the terminal is open, logged in and connected

Expert advisors usually need a VPS because they only run while their MetaTrader terminal is open and online, and a personal computer that sleeps, reboots or loses internet will stop the EA. A virtual private server is a remote computer that stays on continuously, so the terminal and its EA keep running even when the trader's own machine is off.

For round-the-clock or fast-moving markets this matters, because a strategy or copier that misses ticks while the terminal is down can miss or mismanage trades. The trade-off is that a VPS is an extra cost and an extra piece of infrastructure the trader has to set up, secure and maintain.

A copier EA is a specific kind of expert advisor whose job is to mirror trades rather than generate them. One EA reads trades on a source MetaTrader account and a partner EA reproduces them on one or more destination accounts, often with adjusted lot sizes. It is still an EA, so it still depends on each MetaTrader terminal staying open and connected.

A cBot is the cTrader equivalent but is not an EA at all. cTrader does not run MQL or expert advisors; its automated programs, called cBots, are written in C# and run inside cTrader's own Automate environment. So an EA and a cBot solve similar problems on different platforms, and code for one does not run on the other.

No. An EA is only required when the automation has to run inside a MetaTrader terminal. Other platforms automate differently: cTrader uses C# cBots, and platforms such as Match-Trader, Binance Futures and Bybit expose REST or WebSocket APIs that an external service can call directly, with no terminal-side program at all.

A cloud execution layer is one alternative to the terminal-plus-EA model. PipSync, for example, runs the parsing and order routing on its own servers and connects to brokers over their APIs or supported integrations, so there is no EA, cBot, plugin or terminal to keep open and no VPS to maintain. PipSync is execution infrastructure, not a strategy or signal provider, and trading leveraged products still carries substantial risk of loss.