You have built the perfect strategy. The logic is sound, the backtest looks green, and you are ready to trade. But when you apply it to the chart, something feels… heavy.

Maybe the script takes ten seconds to load. Maybe your alerts are firing late. Or worse, maybe the “Buy” signal you saw ten minutes ago has mysteriously vanished from the chart.

These aren’t just “glitches”—they are logic and performance bugs. In algorithmic trading, speed is edge. A script that lags, repaints, or times out can cost you real money.

As a professional developer, I see the same 10 mistakes in almost every client script I fix. Here is how to identify them and, more importantly, how to fix them.

1. The “Repainting” Ghost (Future Leak)

This is the most dangerous bug of all. It happens when your script calculates data based on the future (e.g., the closing price of a candle that hasn’t closed yet). It makes your backtest look perfect, but destroys your live trading.

• The Bug: Using request.security with lookahead=barmerge.lookahead_on improperly.
• The Fix: Always be careful with lookahead. If you are using it for historical analysis, ensure you are offsetting the data so you don’t read the future.
• Read more on how I solve this: How to Fix Repainting in Pine Script: A Developer’s Guide

2. The “Loop from Hell” (Execution Timeout)

Pine Script has a limit on how long a script can take to calculate. If you try to loop through every single bar (thousands of candles) on every tick, your script will crash with an “Execution time limit exceeded” error.

• The Bug: Using for loops to calculate averages or highs/lows manually.
• The Fix: Use built-in functions. They are optimized C++ under the hood and run 100x faster than your manual loops.
  • Bad: for i = 0 to 14 ...
  • Good: ta.sma(close, 14)

3. Redundant Security Calls (Network Lag)

Every time you call request.security, TradingView has to fetch data. Doing this 20 times for different variables slows down your loading time significantly.

• The Bug: Calling request.security separately for Open, High, Low, and Close.
• The Fix: Use Tuples. You can fetch multiple values in a single call.Pine Script// Efficient [dOpen, dHigh, dClose] = request.security(syminfo.tickerid, "D", [open, high, close])

4. The calc_on_every_tick Drain

By default, strategies calculate only when a bar closes. If you force them to calculate on every price tick (which happens hundreds of times a second in crypto), you are burning resources unnecessarily.

• The Bug: Using calc_on_every_tick=true when you don’t actually need intra-bar execution.
• The Fix: Set it to false unless you are scalping seconds-based charts.

5. The Drawing Limit (Visual Clutter)

TradingView limits the number of lines, labels, and boxes you can draw on a chart (usually around 50-500). If you don’t manage this, your old support lines will disappear randomly.

• The Bug: Creating a new line.new on every bar without deleting old ones.
• The Fix: Use a garbage collection logic or the max_lines_count parameter in your indicator() settings to automatically delete the oldest ones.

6. The “Max Bars Back” Error

This cryptic error crashes your script when you try to reference data too far in the past without warning the compiler.

• The Bug: Calculating a variable based on a dynamic length that Pine Script can’t predict.
• The Fix: Force a buffer size using the max_bars_back() function.Pine Scriptmax_bars_back(close, 500) // Forces Pine to keep 500 bars of history

7. Alert Spam (Message Limits)

If your logic triggers an alert on “Every Tick,” and the price hovers around your entry point, you might get 500 emails in one minute. This isn’t just annoying; TradingView will block your webhook.

• The Bug: Using alert.freq_all on a condition that flickers.
• The Fix: Use alert.freq_once_per_bar or alert.freq_once_per_bar_close.
• Need help setting this up? Read: Setting Up Pine Script Alerts for Auto Trading

8. Variable Scope Issues (var vs. varip)

Sometimes your variables reset to zero on every candle, forgetting the trend you were tracking.

• The Bug: Using float myVar = 0 instead of var float myVar = 0.
• The Fix:
  • Use var if you want the value to remember its state from the previous candle.
  • Use varip if you want the value to persist intra-bar (essential for real-time tick logic).

9. Version Lag (Using Outdated Code)

Pine Script v3 and v4 are significantly slower and lack the library features of v5 and v6.

• The Bug: Copy-pasting 3-year-old code that uses inefficient array handling.
• The Fix: Migrate your code. Version 5/6 offers libraries and better array management that reduce script load.
• Should you upgrade? Read: Pine Script v5 vs v4 vs v6: Should You Migrate?

10. The Indicator Limit (Free Plan Blocks)

This isn’t a code bug, but a platform constraint that stops your strategy. You try to add RSI, MACD, and Bollinger Bands, and TradingView says “Upgrade Plan.”

• The Bug: Having 5 separate scripts for 5 indicators.
• The Fix: Combine them all into one single “Super-Script.”
• Learn how: How to Combine Multiple Indicators Into One Pine Script

Don’t want to spend your weekend debugging?

Identifying these bugs is half the battle; fixing them without breaking your logic is the other half. One wrong bracket, and your strategy stops working.

Don’t know coding? We do it for you.

We specialize in optimizing heavy scripts, fixing repainting issues, and converting manual logic into lightning-fast bots.