The quest for an is one of the most persistent searches in the MetaTrader community. Whether you’ve lost the source code to an old Expert Advisor (EA) or you're trying to understand the logic behind a "black box" indicator, the need to reverse-engineer these files is common.
If you purchased the EA, most developers will provide the source code for a fee or help you with updates.
Some developers host projects that attempt to "disassemble" the file into assembly-like code. While technically impressive, this won't give you a readable .mq4 file that you can edit and recompile easily. The Technical Reality: Decompilation vs. Recovery It is important to distinguish between two different goals:
These often contain a README.md file with a link to an external website or a password-protected .zip file. Exercise extreme caution. These are frequently used to distribute malware or "stealers" designed to grab your MT4 login credentials or crypto keys.