How to Use MQL5 for Automated Trading on MetaTrader 5
MQL5 is the language used to develop Expert Advisors, custom indicators, scripts, and libraries for MetaTrader 5. A useful first workflow is to create a small program in MetaEditor, compile it, inspect its behavior in a controlled test, and only then add trading logic. Compilation alone does not establish that orders are correct or a strategy is profitable.
Set up the project in the correct terminal
Install MT5 from MetaQuotes or your broker's verified source. Open MetaEditor with F4 or the terminal's language-editor command. In MT5, File → Open Data Folder identifies the active installation's data directory; this avoids editing one installation while running another.
Use MQL5/Experts for EAs, MQL5/Indicators for indicators, and MQL5/Scripts for one-run scripts. Include files belong under MQL5/Include; compiled libraries have their own MQL5/Libraries location. Keep source .mq5 files distinct from compiled .ex5 files.
Create a project with the MQL5 Wizard. An EA template supplies a starting structure; it does not supply a complete trading system. The separate generated-EA workflow can assemble available modules, which still need testing against your intended rules.
Match the event handler to the program
| Handler | Typical purpose | Important boundary |
|---|---|---|
OnInit() | Validate inputs and allocate resources | Reinitialization can occur after relevant changes |
OnTick() | Handle new quotes for an EA's chart symbol | It is not an indicator calculation callback |
OnCalculate() | Calculate a custom indicator's buffers | Use its history and prev_calculated arguments correctly |
OnStart() | Execute a script's task | Not a continuously running EA loop |
OnDeinit() | Release resources and log shutdown context | Plan for removal and reinitialization |
An EA need not put every operation in OnTick(). Events are processed sequentially, and a new tick event is not queued when one is already queued or processing. Disabling automated trading prevents EA trade requests but does not stop its calculation callbacks. These details are documented in OnTick.
Read indicator values through handles
In MQL5, iMA() returns an indicator handle, not the current moving-average value. Create and validate the handle, check that data is available, and use CopyBuffer() to retrieve the required values. Inspect the number of values copied and distinguish the developing bar from completed bars. Release unneeded handles during cleanup. See the iMA reference.
For a crossover, comparing two current values is insufficient: compare their relationship on the current evaluation bar with the prior bar as well. Decide whether the EA evaluates each tick or once per completed bar, and prevent duplicate entries under repeated callbacks.
Custom indicators bind arrays with SetIndexBuffer() and calculate them in OnCalculate(). MQL5 uses the prev_calculated parameter for incremental work; IndicatorCounted() is an MQL4 pattern, not the correct substitute. History changes can reset prev_calculated to zero. See OnCalculate.
Validate the trade request and resulting state
Before an order, check the symbol's volume step, minimum size, stop restrictions, allowed filling mode, margin, and account mode. Netting and hedging accounts can require different position-management logic.
OrderSend() returning true does not prove a trade executed. Inspect the result's return code and follow the resulting order/deal/position state; one request can lead to several trade transactions. MetaQuotes explains this in OrderSend. Log useful identifiers and rejection reasons rather than treating an absence of compilation errors as successful trading.
Compile, backtest, and forward-test separately
Compile with F7, review errors and warnings, and confirm that the intended executable appears in the terminal. Use Strategy Tester with the target symbol, dates, costs, and suitable modeling mode. The tester offers configurable execution-delay modeling; it is inaccurate to say it cannot model any delay, although a model cannot reproduce every live condition.
Reserve data outside parameter selection and inspect individual trades. Then use a demo account to test startup, disconnections, reinitialization, duplicate signals, and order rejection. A terminal or hosting environment must remain available for an EA to run, and instrument trading hours still apply.
The Pineify MQL5 Coding Agent can help draft or revise .mq5 source. Give it explicit entry, exit, sizing, account-mode, and error-handling requirements. Compile the output in the intended MetaEditor version and test it; AI assistance does not guarantee compilable code, correct execution, or a measurable reduction in development time.
Can I paste Pine Script into MetaEditor?
No. Pine Script and MQL5 have different APIs and execution models. Translate the rules and validate the MQL5 implementation separately.
Does an EA template already trade?
A template provides structure. Trading behavior requires implemented rules or generated modules, plus validation and the appropriate permissions.
Does a successful OrderSend call mean my position is open?
Not necessarily. Inspect the return code and resulting order, deal, and position state.