# Cairo Variables Mutability

> Explain Cairo variable bindings, immutability, `mut`, constants, and shadowing; use when a request involves variable declaration, reassignment errors, changing types via shadowing, or defining constants in Cairo.

- Skill: `teddyjfpender/cairo-variables-mutability` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add teddyjfpender/cairo-variables-mutability`
- Raw SKILL.md: https://api.skillmd.com/api/skills/teddyjfpender/cairo-variables-mutability/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: teddyjfpender (https://skillmd.com/u/teddyjfpender)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/teddyjfpender/cairo-variables-mutability

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# Cairo Variables and Mutability

## Overview
Guide variable bindings in Cairo, including immutability, mutation with `mut`, constants, and shadowing.

## Quick Use
- Read `references/variables-mutability.md` before answering.
- Provide short, compile-ready examples that show correct use of `let`, `let mut`, `const`, and shadowing.
- When addressing errors, point to the specific rule violated (immutability, type change, or scope).

## Response Checklist
- Decide whether the variable should be immutable, mutable, or constant.
- If the name is reused or the type changes, prefer shadowing with a new `let`.
- For constants, require `const`, a type annotation, and global scope.

## Example Requests
- "Why does `x = 6` fail after `let x = 5` in Cairo?"
- "Should I use `mut` or shadowing when converting `u64` to `felt252`?"
- "How do I declare a constant in Cairo?"

## Cairo by Example
- [Variable Bindings](https://cairo-by-example.xyz/variable_bindings)
- [Mutability](https://cairo-by-example.xyz/variable_bindings/mut)
- [Scope and Shadowing](https://cairo-by-example.xyz/variable_bindings/scope)
- [Freezing](https://cairo-by-example.xyz/variable_bindings/freeze)
- [Constants](https://cairo-by-example.xyz/custom_types/constants)