5 MQL5 Debugging Tips for MetaTrader 5 Developers

Ozdemir — Sat, 10 Oct 2026 04:15:48 +0000

When working with MQL5, I try not to jump straight into changing code as soon as something goes wrong. First, I want to understand what the program is supposed to do, what it actually does, and where the difference begins.

Here are five checks that help me approach debugging more systematically.

1. Read the compiler errors carefully

The MetaEditor compiler output is usually the first place I look when a program fails to compile.

I check the reported line number, error description, and surrounding code. Sometimes one missing semicolon or mismatched bracket can cause several additional errors to appear.

Rather than fixing every reported line blindly, I look for the earliest meaningful error first.

2. Check variable types and declarations

MQL5 has different data types for integers, floating-point values, strings, Boolean values, and more.

Using the wrong type or referencing an undeclared variable can cause compilation errors or unexpected behavior.

I also check whether variables are declared in the correct scope and whether their values are initialized before use.

3. Verify function parameters and return values

When a function doesn't behave as expected, I check its parameters, return type, and how it is called.

For built-in MQL5 functions, I refer to the official documentation rather than guessing the expected arguments.

This is especially useful when working with unfamiliar trading, order-management, or market-data functions.

4. Use logs to understand runtime behavior

A program can compile successfully and still behave incorrectly when running.

The Experts and Journal tabs in MetaTrader 5 can provide useful information about runtime errors, rejected requests, and other events.

Adding targeted Print() statements can also help reveal the values a program is receiving and the path its logic is following.

5. Test one change at a time

When several changes are made together, it becomes harder to identify which change fixed the problem—or introduced another one.

I prefer to make a focused change, compile again, and test the affected behavior before moving to the next issue.

For trading software, testing should be performed in an appropriate demo or controlled environment before considering live use.

Final thoughts

Debugging is not just about removing compiler errors. It's about understanding why the program behaves the way it does.

A systematic process makes it easier to isolate problems, verify fixes, and maintain code over time.

What's your first step when debugging an MQL5 program: checking compiler errors, reviewing the logic, or inspecting runtime logs?

What I Learned Building and Testing Forex EAs in MQL5

Ozdemir — Thu, 08 Oct 2026 15:50:31 +0000

What I Learned Building and Testing Forex EAs in MQL5

I've spent a lot of time working with and testing Expert Advisors (EAs) for MetaTrader 5, and one thing I've learned is that getting an EA to open trades is the easy part.

The difficult part is building something that behaves correctly when market conditions change.

When developing an EA, I pay attention to things like:

Proper entry and exit logic
Stop loss and take profit handling
Risk and lot-size management
Drawdown control
Spread and slippage
Trade management
Breakeven and trailing logic
Economic news conditions
Making sure the EA doesn't rely on dangerous recovery methods

I've also learned that a good backtest doesn't automatically mean a good EA.

An EA can look impressive in a short backtest and behave completely differently on a live account because of spreads, execution, slippage and changing market conditions.

That's why I prefer to test the actual logic under different market conditions rather than focusing only on the final profit number.

For me, EA development is not just about creating something that can trade.

It's about creating software that follows its rules consistently and handles unexpected situations properly.

I'm currently continuing to work with MQL5 and explore different approaches to automated trading.

I'd be interested to hear from other MQL5 developers:

What's the biggest lesson you've learned from developing or testing trading algorithms?

DEV Community: Ozdemir

5 MQL5 Debugging Tips for MetaTrader 5 Developers

1. Read the compiler errors carefully

2. Check variable types and declarations

3. Verify function parameters and return values

4. Use logs to understand runtime behavior

5. Test one change at a time

Final thoughts

What I Learned Building and Testing Forex EAs in MQL5

What I Learned Building and Testing Forex EAs in MQL5