Coding Cairo

Rules and patterns for writing efficient Cairo code. Sourced from audit findings and production profiling.

When to Use

• Implementing arithmetic (modular, parity checks, quotient/remainder)
• Optimizing loops (slow iteration, repeated .len() calls, index-based access)
• Splitting or assembling integer limbs (u256 → u128, u32s → u128, felt252 → u96)
• Packing struct fields into storage slots
• Using BoundedInt for zero-overhead arithmetic with compile-time bounds
• Choosing integer types (u128 vs u256, BoundedInt vs native types)

Not for: Profiling/benchmarking (use benchmarking-cairo)

Quick Reference — All Rules