The safest decompiler is the one you never run. Keep backups of your MQ4 files on GitHub, GitLab, or even a simple USB drive. If you need to modify an EA without source code, learn MQL4 yourself and rebuild it — that skill will be worth more than any decompiler's empty promise.

What follows is a detailed, expert-level article explaining why such tools are dangerous, why they don’t work as advertised, and what you should do instead if you have lost your original MQ4 source code. Introduction: The Holy Grail That Doesn’t Exist Every MetaTrader 4 (MT4) developer or trader has been there: you have a compiled Expert Advisor (EX4 file) running on your charts, but the original source code (MQ4) is lost due to a hard drive crash, a corrupted USB stick, or a developer who disappeared. Desperate to edit a single parameter or fix a bug, you search online for an “EX4 to MQ4 decompiler.”

It is important to address the core of your request directly: that can reliably decompile a compiled EX4 file back into the original, editable MQ4 source code with full accuracy.

Stay safe, and may your stop losses never be hunted.