Convert Pine Script to MQL5: What Survives and What Breaks

There is a moment in every TradingView-to-MetaTrader conversion where the trader asks the same question: it's eighteen lines, why is this not a twenty-minute job?

Fair question. The answer is that Pine and MQL5 disagree about almost everything beneath the syntax, and the disagreements are invisible until you go looking. Here is what actually happens to a script on the way across, piece by piece, so you know what you are paying for and where the risk sits.

Your maths survives intact

Let's start with the good news. The arithmetic transfers cleanly. A moving average is a moving average, an RSI period of 14 means the same thing on both platforms, and your crossover condition means what it meant before.

Expect small numerical drift, though. Built-in indicators differ slightly across platforms in how they seed initial values and handle edge cases, so your MQL5 version may print a value a hair off from the TradingView one. 

On a trend filter, this is noise. On a strategy that triggers when two lines sit within a few points of each other, that hair matters, and it is worth knowing which kind of strategy you have before anyone starts coding.

Your bar references get turned around

Pine counts backwards from now. close[1] is the previous bar, and the language handles history for you without being asked.

MQL5 makes you say what you mean. You declare arrays, you copy the data you want, and depending on how the array is set up, index zero is either the current bar or the oldest one on the chart. Get that backwards and the code compiles happily, runs without complaint, and produces signals that reference the wrong candles.

This is the single most common source of silent bugs in converted scripts. Nothing errors. The chart just fills with entries that look almost right, and it takes a careful comparison against the original to see that they fire a bar late or a bar early.

Your execution model gets replaced

Here is the deep one, and it is why the line count roughly doubles or triples.

Pine runs top to bottom across the chart, bar by bar. Your script is one continuous piece of logic, and the platform walks it through history for you.

MQL5 does none of that. It waits. A tick arrives, and it runs OnTick. A new bar forms and your code has to notice. Nothing runs unless an event fires, and your logic has to be broken apart and reassembled around those events. Variables that Pine remembered between bars for free now have to be declared as statics or class members and managed by hand.

So the conversion is not a translation. It is a rebuild of the same idea inside a different architecture, which is why the automated converters produce something that compiles and then behaves nothing like the original.

An eighteen-line Pine script commonly lands somewhere around forty-five lines of MQL5, and that ratio holds fairly well as scripts grow.

Your multi-timeframe calls need auditing, not just converting

If your script calls request.security to pull a higher timeframe, stop before converting anything and ask whether the original repaints.

Pine's security function, used without care, shows you values on historical bars that were not available at the time. The backtest looks superb because the script effectively saw the future. Traders often do not know their favourite indicator does this, because on the chart it looks fine.

MQL5 will not reproduce that behaviour, and it should not. So one of two things happens. Either the converted version underperforms the TradingView backtest, and the trader assumes the conversion is broken, or an honest developer tells them the original was repainting and the edge was never real. The second conversation is uncomfortable and worth having before the invoice, not after.

Your strategy calls hide an entire engine

strategy.entry looks like one line. It is not.

Behind it sits a position management system that TradingView provides for free: pyramiding rules, automatic reversal when you flip direction, position sizing, order tracking, and the accounting that keeps it all coherent.

MQL5 gives you none of that. Every piece has to be written. Opening the position, tracking it, deciding what a second signal means while a trade is already running, handling the reversal, placing the stop and target, and dealing with partial fills and requotes that TradingView's simplified fill model never had to think about.

This is why converting an indicator is a modest job and converting a strategy is a real one. The indicator draws. The strategy trades, and trading is where the platform's hidden helpfulness stops being available.

Your backtest will not match, and that is not a bug

Once it runs, the numbers will differ from TradingView. Different data feed, a tester that models spread and slippage instead of idealised fills, tick-level execution against bar-level assumptions, and small indicator variations all stack up.

A modest gap in profit factor is normal and expected. A large one means something is wrong in the logic and needs finding. Occasionally the MQL5 version does better, because tick simulation catches intrabar entries the bar-level model never saw.

The useful test is not whether the equity curves match. It is whether the two versions take the same trades at the same bars. Line up the entries, and any divergence points straight at the bug.

Worth knowing before you order one

If you have a Pine indicator you want on your MetaTrader charts, that is usually a clean job. Plot logic, alerts, buffers, done.

If you have a Pine strategy you want trading live, you are ordering a rebuild, and the questions worth answering upfront are: does the original use request.security, and if so does it repaint? Does it rely on strategy calls with pyramiding or reversal behaviour? Does it trigger on bar close or intrabar? Each of those answers changes the scope, and any developer who does not ask them is guessing at your quote.

We handle Pine Script and TradingView conversions to both MQL4 and MQL5 at Keenbase, and the first thing we do with a script is read it for exactly the traps above, then tell you what we found before quoting.

Sometimes that conversation saves a trader from paying to automate a strategy that only looked profitable because it was reading ahead. If you want your script properly assessed and converted to trade the way it appears to be,

[send us the script and we will tell you what it will take]