23/09/2026
A converted Expert Advisor that compiles without a single error is not evidence the conversion worked.
The characteristic MT4 to MT5 failure does not produce anything wrong to find. It produces an absence — something that should have happened and didn't. That distinction decides which of your tools can help, because the compiler, the Strategy Tester and the demo account are all error detectors, and this failure class does not produce errors.
One break-even manager held three open positions and moved none of them. Its loop counted OrdersTotal(), which on MT5 counts pending orders only, so it found zero and did nothing. Nothing errored. Nobody looked. Time to detection: indefinite.
Since MetaTrader 5 build 6060 in July 2026, MetaEditor ships an AI assistant free on the MQL5 Lite plan, and one of MetaQuotes' own example prompts converts an MQL4 EA to MQL5. The conversion is one prompt away. The checking is not.
The video walks through the three cases and the five-check parity test that catches them.