14 Aug 2025
“Decompiler Accuracy: Can You Really Recover Original MQL4 Logic from EX4?”
Decompiler Accuracy: Can You Really Recover Original MQL4 Logic from EX4?
Meta Description:
Wondering if EX4 decompilers can perfectly restore MQL4 source code? Learn how accurate decompilation really is, the challenges, and what traders need to know.
Introduction
In the world of MetaTrader 4 (MT4), the difference between EX4 and MQ4 files is crucial. EX4 files are compiled, machine-readable versions of MQ4 source code — meaning they can run in MT4 but can’t be edited.
Naturally, some traders and developers ask:
“Can I decompile an EX4 back into the original MQL4 logic?”
The answer isn’t as simple as yes or no. In this post, we’ll break down how accurate EX4 decompilation really is, what’s lost in the process, and why even the best decompilers have limitations.
What is EX4 Decompilation?
Decompilation is the process of taking compiled EX4 code and converting it back into human-readable MQL4 format.
• Goal: Recover the original trading logic.
• Tools: Decompiler software or services.
• Challenges: MT4 build versions, encryption, and code obfuscation.
Can You Get 100% of the Original Code Back?
In short: No — at least not perfectly.
Here’s why:
1. Variable & Function Names Are Lost
When MQ4 is compiled into EX4, meaningful names like TakeProfit or RiskPerTrade are replaced with generic placeholders like var_1 or func_3.
2. Comments Are Completely Removed
Any notes, explanations, or documentation in the original code are stripped away.
3. Formatting is Flattened
Indentation and spacing disappear, making the recovered code harder to read.
4. Optimizations Change the Logic Flow
MT4’s compiler may rearrange or optimize code during compilation, so the decompiled version may not match the exact structure of the original.
Accuracy Factors
The accuracy of EX4 decompilation depends on:
1. MT4 Build Version
• Before Build 600: Decompilation was easier and often produced more readable results.
• After Build 600: Stronger encryption and obfuscation make accurate recovery extremely difficult.
2. Quality of the Decompiler
• Some tools are outdated and can’t handle newer EX4 formats.
• High-end private decompilers may recover more readable code but still won’t restore original names or comments.
3. Complexity of the Original Code
• A simple moving average EA is easier to decompile than a complex neural-network-based EA.
• The more advanced the logic, the more it gets scrambled during compilation.
What the Decompiled Code Looks Like
A typical decompiled MQL4 file will:
• Have generic variable names (a1, a2, a3).
• Lack any comments.
• Still contain the same logic flow — meaning the program will work the same way — but it’s harder to understand and modify.
Legal & Ethical Considerations
Before attempting any EX4 decompilation, remember:
• Without permission, it’s illegal under copyright laws and violates MetaTrader’s terms of service.
• You should only decompile your own EX4 files or those you have explicit rights to edit.
Why Traders Should Care
• If you lose your MQ4 file, don’t expect a perfect recreation from EX4.
• If you sell your EA as EX4, know that some parts of the logic can still be reverse-engineered.
• If you’re buying an EA, request the MQ4 source code if you plan to make changes.
Best Practices
• Always keep backups of your MQ4 source code.
• Use code obfuscation to make decompilation harder.
• Work with trusted developers and secure contracts when outsourcing.
