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name, description, version, license, compatibility, metadata
name description version license compatibility metadata
mql5 MQL5 development skill for MetaTrader 5 Expert Advisors, Indicators, Scripts, and Services. Focus on positions, orders, indicators, ticks, bars, risk management, backtesting, and multi-instance MT5 operations. Includes programming book and API reference documentation. 0.1 MIT Target: MetaTrader 5 platform. Language: MQL5 (C++-like syntax). File extensions: *.mq5 (source), *.mqh (headers). Run time: Windows native, Linux via Wine, macOS via Wine.
project-version focus-areas
0.1.0
positions
orders
indicators
ticks
bars
risk-management
backtesting

MQL5 Development Skill

Expert development skill for MetaTrader 5. Covers EA, Indicator, Script, and Service creation with emphasis on trading operations, technical indicators, multi-timeframe analysis, risk management, and backtesting workflows.

1. MQL5 Fundamentals

Language and File Types

  • MQL5 syntax is similar to C++ but with domain-specific additions
  • Source files: *.mq5 (programs), *.mqh (headers)
  • Compiled output: *.ex5 (same name as source)
  • Compiler: built into MetaEditor IDE

Program Types

Type Purpose Key Handler Directory
Expert Advisor Automated trading OnTick() MQL5/Experts/
Indicator Technical analysis OnCalculate() MQL5/Indicators/
Script One-shot execution OnStart() MQL5/Scripts/
Service Background task OnStart() + OnTimer() MQL5/Services/

MQL5 Directory Structure

Default locations per platform:

Platform Path
Windows 10+ $env:USERPROFILE\AppData\Roaming\MetaQuotes\Terminal\$INSTANT_HEX\MQL5
Linux (Wine) ~/.wine/drive_c/Program Files/MetaTrader 5/MQL5/
macOS Unknown — verify per installation

Key subdirectories:

MQL5/
├── Experts/          # EA source files (.mq5)
│   ├── Examples/     # Built-in example EAs
│   └── Free Robots/  # Downloaded EAs
├── Indicators/       # Indicator source files
├── Scripts/          # Script source files
├── Services/         # Service source files
├── Include/          # Header files (.mqh)
│   ├── Trade/        # Trading classes (Trade.mqh, PositionInfo.mqh, etc.)
│   ├── Indicators/   # Indicator helpers
│   ├── Expert/       # Expert base classes
│   └── Generic/      # Generic collections
├── Files/            # File I/O sandbox
├── Images/           # Image resources
├── Libraries/        # DLL/shared libraries
├── Profiles/         # Chart profiles
└── Logs/             # Log files

Multi-Instance MT5

Multiple MT5 instances can run simultaneously for different accounts:

  1. Install MT5 to separate target paths (e.g. MT5_BrokerA/, MT5_BrokerB/)
  2. Each instance has its own MQL5/ directory
  3. To identify which account an instance is logged into:
    • AccountInfoInteger(ACCOUNT_LOGIN) — account number
    • AccountInfoString(ACCOUNT_NAME) — account name
    • AccountInfoString(ACCOUNT_SERVER) — broker server
  4. Each instance runs as a separate process — use Magic Number to distinguish EA trades across instances on the same symbol

2. Trading Operations

Core Concepts

  • Order: instruction to buy/sell (Market or Pending)
  • Deal: executed exchange (buy at Ask, sell at Bid)
  • Position: current obligation (long or short)

CTrade Class (Standard Library)

#include <Trade\Trade.mqh>

CTrade trade;

// Setup in OnInit()
trade.SetExpertMagicNumber(EA_MAGIC);
trade.SetMarginMode();
trade.SetTypeFillingBySymbol(Symbol());
trade.SetDeviationInPoints(Slippage);

Key methods:

Method Purpose
PositionOpen(symbol, type, volume, price, sl, tp) Open a position
PositionClose(symbol, deviation) Close a position
PositionModify(symbol, sl, tp) Modify SL/TP
PositionClosePartial(symbol, volume) Partial close
Buy(volume, price, sl, tp, comment) Shortcut for buy
Sell(volume, price, sl, tp, comment) Shortcut for sell
BuyLimit/BuyStop/SellLimit/SellStop(...) Pending orders
ResultRetcode() Check trade server return code
ResultDeal() Get deal ticket after execution

Position Queries

// Iterate open positions (Hedging account)
uint total = PositionsTotal();
for (uint i = 0; i < total; i++) {
    string sym = PositionGetSymbol(i);
    if (sym == _Symbol && PositionGetInteger(POSITION_MAGIC) == EA_MAGIC) {
        double vol = PositionGetDouble(POSITION_VOLUME);
        double sl  = PositionGetDouble(POSITION_SL);
        double tp  = PositionGetDouble(POSITION_TP);
        long   type = PositionGetInteger(POSITION_TYPE);
    }
}

// Netting account — simpler
if (PositionSelect(_Symbol)) {
    // position is selected
}

Order Execution Pattern

// Calculate price
double price = (signal == ORDER_TYPE_BUY)
    ? SymbolInfoDouble(_Symbol, SYMBOL_ASK)
    : SymbolInfoDouble(_Symbol, SYMBOL_BID);

// Open with SL/TP
trade.PositionOpen(_Symbol, signal, lotSize, price, sl, tp, "EA Signal");

// Always check result
if (trade.ResultRetcode() != TRADE_RETCODE_DONE) {
    Print("Trade failed: ", trade.ResultRetcode());
}

Hedging vs Netting

bool IsHedging = ((ENUM_ACCOUNT_MARGIN_MODE)
    AccountInfoInteger(ACCOUNT_MARGIN_MODE) == ACCOUNT_MARGIN_MODE_RETAIL_HEDGING);
  • Hedging: multiple positions per symbol, must iterate and match Magic Number
  • Netting: one position per symbol, use PositionSelect()

3. Indicators and Multi-Timeframe

Built-in Indicator Handles

// Moving Average
int handle = iMA(_Symbol, PERIOD_H1, 50, 0, MODE_SMA, PRICE_CLOSE);

// RSI
int handle = iRSI(_Symbol, PERIOD_H1, 14, PRICE_CLOSE);

// MACD
int handle = iMACD(_Symbol, PERIOD_H1, 12, 26, 9, PRICE_CLOSE);

// Bollinger Bands
int handle = iBands(_Symbol, PERIOD_H1, 20, 0, 2.0, PRICE_CLOSE);

Reading Indicator Values

double buffer[];
ArraySetAsSeries(buffer, true);
if (CopyBuffer(handle, 0, 0, 3, buffer) != 3) {
    Print("No indicator data");
    return;
}
// buffer[0] = current bar value
// buffer[1] = previous bar value

Multi-Timeframe Analysis

// Higher timeframe trend
int h4_ma = iMA(_Symbol, PERIOD_H4, 50, 0, MODE_SMA, PRICE_CLOSE);

// Entry timeframe signal
int h1_rsi = iRSI(_Symbol, PERIOD_H1, 14, PRICE_CLOSE);

// In OnTick():
double h4_val[], h1_val[];
CopyBuffer(h4_ma, 0, 0, 1, h4_val);
CopyBuffer(h1_rsi, 0, 0, 1, h1_val);

bool bullish = (SymbolInfoDouble(_Symbol, SYMBOL_BID) > h4_val[0]);
bool oversold = (h1_val[0] < 30);

New Bar Detection

datetime lastBarTime = 0;

void OnTick() {
    datetime currentBarTime = iTime(_Symbol, _Period, 0);
    if (currentBarTime == lastBarTime) return;  // not a new bar
    lastBarTime = currentBarTime;
    // New bar — run analysis here
}

4. Ticks and Bars

Timeseries Access

Index 0 = current (unfinished) bar. Array is reverse-ordered.

MqlRates rates[];
ArraySetAsSeries(rates, true);
CopyRates(_Symbol, _Period, 0, 100, rates);

// rates[0] = current bar
// rates[1] = previous bar
// rates[0].open, .high, .low, .close, .tick_volume, .time

Tick Data

MqlTick tick;
SymbolInfoTick(_Symbol, tick);
// tick.bid, tick.ask, tick.last, tick.volume, tick.time

Key Functions

Function Purpose
CopyRates() Bulk OHLCV data
CopyOpen/High/Low/Close() Individual price arrays
CopyTime() Bar open times
CopyBuffer() Indicator buffer values
iBars() Bar count for symbol/period
iBarShift() Bar index by time
iTime() Bar open time by shift
SymbolInfoTick() Current tick data

5. Risk Management and Lot Sizing

Fixed Percentage Risk

double CalculateLotSize(double riskPercent, double slPoints) {
    double accountBalance = AccountInfoDouble(ACCOUNT_BALANCE);
    double riskAmount = accountBalance * riskPercent / 100.0;

    double tickValue = SymbolInfoDouble(_Symbol, SYMBOL_TRADE_TICK_VALUE);
    double tickSize  = SymbolInfoDouble(_Symbol, SYMBOL_TRADE_TICK_SIZE);
    double point     = SymbolInfoDouble(_Symbol, SYMBOL_POINT);

    if (tickValue == 0 || tickSize == 0 || slPoints == 0) return 0;

    double slMoneyPerLot = (slPoints * point / tickSize) * tickValue;
    double lot = riskAmount / slMoneyPerLot;

    // Normalize to broker constraints
    double minLot  = SymbolInfoDouble(_Symbol, SYMBOL_VOLUME_MIN);
    double maxLot  = SymbolInfoDouble(_Symbol, SYMBOL_VOLUME_MAX);
    double lotStep = SymbolInfoDouble(_Symbol, SYMBOL_VOLUME_STEP);

    lot = MathFloor(lot / lotStep) * lotStep;
    lot = MathMax(lot, minLot);
    lot = MathMin(lot, maxLot);

    return NormalizeDouble(lot, 2);
}

Risk-to-Reward Ratio

// Minimum 1:2 RR
double slDistance = MathAbs(price - sl);
double tpDistance = slDistance * 2;  // 1:2 minimum
double tp = (orderType == ORDER_TYPE_BUY) ? price + tpDistance : price - tpDistance;

Position Sizing Rules

  1. Never risk more than 1-2% per trade
  2. Calculate lot size from risk amount and SL distance
  3. Normalize to broker's lot step and min/max constraints
  4. Account for spread when calculating SL distance

6. Backtesting and Optimization

Strategy Tester

The Strategy Tester is built into MT5. Key concepts:

  1. Single Test: run EA once with fixed parameters
  2. Optimization: genetic algorithm searches parameter space
  3. Custom Criterion: OnTester() returns optimization value

OnTester Handler

double OnTester() {
    // Called after each test pass
    // Return value used as "Custom max" optimization criterion

    double profit   = TesterStatistics(STAT_PROFIT);
    double dd       = TesterStatistics(STAT_BALANCE_DDREL_PERCENT);
    double trades   = TesterStatistics(STAT_TRADES);
    double pf       = TesterStatistics(STAT_PROFIT_FACTOR);
    double sharpe   = TesterStatistics(STAT_SHARPE_RATIO);

    // Minimum trade count filter
    if (trades < 50) return 0;

    // Custom criterion: profit factor * (1 - max drawdown%)
    return pf * (1.0 - dd / 100.0);
}

Key Statistics

Stat Description
STAT_PROFIT Net profit/loss
STAT_PROFIT_FACTOR Gross profit / gross loss
STAT_BALANCE_DDREL_PERCENT Max balance drawdown %
STAT_SHARPE_RATIO Sharpe ratio
STAT_TRADES Number of trades
STAT_PROFIT_TRADES Winning trades
STAT_LOSS_TRADES Losing trades
STAT_EXPECTED_PAYOFF Average profit per trade
STAT_RECOVERY_FACTOR Profit / max drawdown

Backtesting Workflow

  1. Code the EA with OnTick(), OnInit(), OnDeinit()
  2. Add OnTester() for custom optimization criterion
  3. In MT5: Strategy Tester → select EA → set symbol/timeframe/period
  4. Choose "Open prices only" for speed, "Every tick" for accuracy
  5. Run single test → check results
  6. Run optimization → find best parameters
  7. Validate with out-of-sample data

Automated Backtesting Loop

EA Development Cycle:
  Code → Compile → Single Test → Check Results
       ↓
  If promising → Optimize → Analyze Results
       ↓
  If validated → Forward Test → Deploy
       ↓
  Monitor → Collect Data → Refine → Repeat

7. Event Handlers Reference

Handler When Called Use Case
OnInit() EA/indicator starts Initialize handles, variables
OnDeinit() EA/indicator stops Cleanup, release handles
OnTick() New tick received EA main logic
OnTimer() Timer event Periodic operations
OnTrade() Trade event React to trade changes
OnTradeTransaction() Trade transaction Detailed trade tracking
OnChartEvent() Chart interaction GUI buttons, objects
OnCalculate() Indicator calculation Indicator main logic
OnTester() Test complete Custom optimization criterion
OnTesterInit() Optimization start Setup for optimization
OnTesterPass() Each optimization pass Log intermediate results

8. Common Pitfalls

  1. Always check ResultRetcode() after PositionOpen() — success != execution
  2. Use SetExpertMagicNumber() to distinguish your EA's trades
  3. Normalize prices with SymbolInfoInteger(_Symbol, SYMBOL_DIGITS)
  4. Check Bars() > N before trading to ensure enough history
  5. Use ArraySetAsSeries(true) for timeseries arrays (index 0 = latest)
  6. Release indicator handles in OnDeinit() with IndicatorRelease()
  7. Don't trade on OnInit() — wait for first OnTick()
  8. Account type matters: Hedging requires iterating positions, Netting uses select
  9. Spread varies: use SymbolInfoInteger(_Symbol, SYMBOL_SPREAD) for live spread
  10. Timer in tester: use EventSetTimer() in OnInit(), not hardcoded delays

9. Quick Reference — EA Skeleton

//+------------------------------------------------------------------+
//|                                            MyExpertAdvisor.mq5   |
//+------------------------------------------------------------------+
#property copyright "Your Name"
#property link      ""
#property version   "1.00"

#include <Trade\Trade.mqh>

input double RiskPercent   = 1.0;    // Risk % per trade
input int    Slippage      = 10;     // Max slippage in points
input int    MagicNumber   = 12345;  // EA magic number

#define EA_MAGIC MagicNumber

CTrade trade;
bool   IsHedging;
datetime lastBarTime = 0;

//+------------------------------------------------------------------+
int OnInit() {
    IsHedging = ((ENUM_ACCOUNT_MARGIN_MODE)
        AccountInfoInteger(ACCOUNT_MARGIN_MODE) == ACCOUNT_MARGIN_MODE_RETAIL_HEDGING);

    trade.SetExpertMagicNumber(EA_MAGIC);
    trade.SetMarginMode();
    trade.SetTypeFillingBySymbol(Symbol());
    trade.SetDeviationInPoints(Slippage);

    return INIT_SUCCEEDED;
}

//+------------------------------------------------------------------+
void OnDeinit(const int reason) {
    // Cleanup
}

//+------------------------------------------------------------------+
void OnTick() {
    // New bar check
    datetime barTime = iTime(_Symbol, _Period, 0);
    if (barTime == lastBarTime) return;
    lastBarTime = barTime;

    // Analysis and trading logic here
    // ...
}

//+------------------------------------------------------------------+
double OnTester() {
    // Custom optimization criterion
    double trades = TesterStatistics(STAT_TRADES);
    if (trades < 30) return 0;
    return TesterStatistics(STAT_PROFIT_FACTOR);
}

10. References

In this skill

  • references/book/ — Programming book (learning path, 581 pages)
    • 00-intro/ — Introduction and IDE
    • 01-basis/ — Language fundamentals
    • 02-oop/ — Object-oriented programming
    • 03-common/ — Common functions (strings, files, math)
    • 04-applications/ — Charts, indicators, objects, events
    • 05-automation/ — Trading, symbols, tester
    • 06-advanced/ — Resources, SQLite, Python, OpenCL
  • references/docs/ — API reference (4135 pages)
    • 19-trading/ — Trading functions (OrderSend, PositionGet, etc.)
    • 16-series/ — Timeseries access (CopyRates, CopyBuffer, etc.)
    • 26-indicators/ — Built-in indicators (iMA, iRSI, iMACD, etc.)
    • 24-customind/ — Custom indicator creation
    • 13-event-handlers/ — Event handlers (OnTick, OnTester, etc.)
    • 34-standardlibrary/ — Standard library (CTrade, CPositionInfo, etc.)

External

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