mql5-indicator-patterns

SKILL.md

MQL5 Visual Indicator Patterns

Battle-tested patterns for creating custom MQL5 indicators with proper display, buffer management, and real-time updates.

Self-Evolving Skill: This skill improves through use. If instructions are wrong, parameters drifted, or a workaround was needed — fix this file immediately, don't defer. Only update for real, reproducible issues.

When to Use This Skill

Use this skill when:

Creating custom MQL5 indicators for MetaTrader 5

Debugging indicator display or buffer issues

Setting up OnCalculate with proper warmup handling

Implementing new bar detection patterns

Quick Reference

Essential Patterns
Display Scale (for small values < 1.0):

IndicatorSetDouble(INDICATOR_MINIMUM, 0.0);
IndicatorSetDouble(INDICATOR_MAXIMUM, 0.1);

Buffer Setup (visible + hidden):

SetIndexBuffer(0, BufVisible, INDICATOR_DATA);        // Visible
SetIndexBuffer(1, BufHidden, INDICATOR_CALCULATIONS); // Hidden

New Bar Detection (prevents drift):

static int last_processed_bar = -1;
bool is_new_bar = (i > last_processed_bar);

Warmup Calculation:

int StartCalcPosition = underlying_warmup + own_warmup;
PlotIndexSetInteger(0, PLOT_DRAW_BEGIN, StartCalcPosition);

Common Pitfalls

Blank Display: Set explicit scale (see Display Scale reference)

Rolling Window Drift: Use new bar detection with hidden buffer (see Recalculation reference)

Misaligned Plots: Calculate correct PLOT_DRAW_BEGIN (see Complete Template reference)

Forward-Indexed Arrays: Always set ArraySetAsSeries(buffer, false)

Key Patterns

For production MQL5 indicators:

Explicit scale for small values (< 1.0 range)

Hidden buffers for recalculation tracking

New bar detection prevents rolling window drift

Static variables maintain state efficiently

Proper warmup calculation prevents misalignment

Forward indexing for code clarity

These patterns solve the most common indicator development issues encountered in real-world MT5 development.

Troubleshooting

Issue
Cause
Solution

Blank indicator window
Scale not set for small values
Set INDICATOR_MINIMUM/MAXIMUM explicitly

Values drifting over time
Rolling window not reset
Use new bar detection with hidden buffer

Misaligned plot start
Wrong PLOT_DRAW_BEGIN
Calculate: underlying_warmup + own_warmup

Reversed array indexing
Series mode enabled
Call ArraySetAsSeries(buffer, false)

Buffer values incorrect
Wrong INDICATOR_DATA type
Use INDICATOR_CALCULATIONS for hidden buffers

Compile error on buffer
Buffer count mismatch
Match #property indicator_buffers with SetIndexBuffer

Indicator not updating
OnCalculate return wrong
Return rates_total to signal successful calculation

Performance issues
Recalculating all bars
Only recalculate from prev_calculated onwards

Reference Documentation

For detailed information, see:

Display Scale - Fix blank indicator windows for small values

Buffer Patterns - Visible and hidden buffer architecture

Recalculation - Bar detection and rolling window state management

Complete Template - Full working example with all patterns

Debugging - Checklist for troubleshooting display issues

Post-Execution Reflection

After this skill completes, check before closing:

Did the command succeed? — If not, fix the instruction or error table that caused the failure.

Did parameters or output change? — If the underlying tool's interface drifted, update Usage examples and Parameters table to match.

Was a workaround needed? — If you had to improvise (different flags, extra steps), update this SKILL.md so the next invocation doesn't need the same workaround.

Only update if the issue is real and reproducible — not speculative.