1---
2name: backtesting-frameworks
3description: Build robust backtesting systems for trading strategies with proper handling of look-ahead bias, survivorship bias, and transaction costs. Use when developing trading algorithms, validating strategies, or building backtesting infrastructure.
4---
5 
6# Backtesting Frameworks
7 
8Build robust, production-grade backtesting systems that avoid common pitfalls and produce reliable strategy performance estimates.
9 
10## When to Use This Skill
11 
12- Developing trading strategy backtests
13- Building backtesting infrastructure
14- Validating strategy performance
15- Avoiding common backtesting biases
16- Implementing walk-forward analysis
17- Comparing strategy alternatives
18 
19## Core Concepts
20 
21### 1. Backtesting Biases
22 
23| Bias             | Description               | Mitigation              |
24| ---------------- | ------------------------- | ----------------------- |
25| **Look-ahead**   | Using future information  | Point-in-time data      |
26| **Survivorship** | Only testing on survivors | Use delisted securities |
27| **Overfitting**  | Curve-fitting to history  | Out-of-sample testing   |
28| **Selection**    | Cherry-picking strategies | Pre-registration        |
29| **Transaction**  | Ignoring trading costs    | Realistic cost models   |
30 
31### 2. Proper Backtest Structure
32 
33```
34Historical Data
35      │
36      ▼
37┌─────────────────────────────────────────┐
38│              Training Set               │
39│  (Strategy Development & Optimization)  │
40└─────────────────────────────────────────┘
41      │
42      ▼
43┌─────────────────────────────────────────┐
44│             Validation Set              │
45│  (Parameter Selection, No Peeking)      │
46└─────────────────────────────────────────┘
47      │
48      ▼
49┌─────────────────────────────────────────┐
50│               Test Set                  │
51│  (Final Performance Evaluation)         │
52└─────────────────────────────────────────┘
53```
54 
55### 3. Walk-Forward Analysis
56 
57```
58Window 1: [Train──────][Test]
59Window 2:     [Train──────][Test]
60Window 3:         [Train──────][Test]
61Window 4:             [Train──────][Test]
62                                     ─────▶ Time
63```
64 
65## Detailed worked examples and patterns
66 
67Detailed sections (starting with `## Implementation Patterns`) live in `references/details.md`. Read that file when the navigation summary above is insufficient.
68 
69## Best Practices
70 
71### Do's
72 
73- **Use point-in-time data** - Avoid look-ahead bias
74- **Include transaction costs** - Realistic estimates
75- **Test out-of-sample** - Always reserve data
76- **Use walk-forward** - Not just train/test
77- **Monte Carlo analysis** - Understand uncertainty
78 
79### Don'ts
80 
81- **Don't overfit** - Limit parameters
82- **Don't ignore survivorship** - Include delisted
83- **Don't use adjusted data carelessly** - Understand adjustments
84- **Don't optimize on full history** - Reserve test set
85- **Don't ignore capacity** - Market impact matters
86