<p>A <strong>custom indicator</strong> is a user‑created technical tool built for the MetaTrader 5 (MT5) platform, written in the <a href="/NewSite/encyclopedia/mql5/" class="ency-link">MQL5</a> programming language. It allows traders to design unique calculations, visualisations, or alerts that are not available in the standard indicator library, extending the analytical capabilities of the trading environment.</p>

<h2>How It Works</h2>
<p>Developers write the indicator’s logic in an MQL5 source file (<code>.mq5</code>). The code defines input parameters, accesses historical price and volume data through built‑in functions (e.g., <code>iClose</code>, <code>iVolume</code>), performs mathematical calculations, and plots results using drawing functions such as <code>PlotIndexSetInteger</code> or <code>IndicatorBuffers</code>. Once compiled, the indicator appears in MT5’s Navigator window and can be attached to any chart, where it updates in real time as new ticks arrive. Users can adjust inputs via the indicator’s properties dialog, test the tool on historical data with the Strategy Tester, and share the compiled <code>.ex5</code> file with others.</p>

<h2>Why It Matters</h2>
<p>Custom indicators enable traders to tailor their analysis to specific strategies or market conditions that standard tools may overlook. For example, a trader could create a volatility‑adjusted moving average that widens during high‑volatility periods and narrows when markets are calm, providing clearer entry signals. This flexibility supports:</p>
<ul>
    <li>Development of proprietary trading systems.</li>
    <li>Integration of alternative data sources, such as sentiment scores.</li>
    <li>Rapid prototyping and backtesting of new ideas without relying on third‑party vendors.</li>
</ul>
<p>By leveraging MQL5’s robust libraries and MT5’s charting engine, custom indicators bridge the gap between generic technical analysis and personalized, data‑driven decision‑making, making them an essential resource for intermediate to advanced traders seeking a competitive edge.</p>