off-by-one

Detect off-by-one errors in Solidity smart contracts and provide remediation guidance.

1|1|Updated Feb 18, 2026
One-click install
npx skills add https://github.com/Apegurus/solidity-argus --skill off-by-one
Or copy as Structured Prompt for Agent
Please help me install this Agent Skill.
Skill: off-by-one
Source: https://github.com/Apegurus/solidity-argus/tree/main/skills/vulnerability-patterns/off-by-one
Command: npx skills add https://github.com/Apegurus/solidity-argus --skill off-by-one

SYSTEM DOCUMENTATION & REQUIREMENTS

💡 This Skill includes references (resource) components.

What problem does it solve?

This Skill identifies and helps remediate off-by-one errors in smart contract code, which can lead to unexpected behavior, data corruption, or security vulnerabilities.

Core Features & Use Cases

  • Vulnerability Detection: Analyzes loops, array accesses, and threshold comparisons for boundary errors.
  • Pattern Matching: Identifies common off-by-one mistakes in Solidity code.
  • Remediation Guidance: Provides clear instructions on how to fix identified issues.
  • Use Case: Ensure that your smart contract correctly processes all elements in an array or accurately enforces a financial threshold without unintended inclusions or exclusions.

Quick Start

Analyze the provided Solidity code for off-by-one vulnerabilities.

Frequently Asked Questions about off-by-one

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I detect off-by-one errors in Solidity smart contracts?

To detect off-by-one errors in Solidity smart contracts, analyze loop boundary conditions, array index calculations, and threshold comparisons for fence-post errors and boundary condition mismatches. This process identifies code patterns that can lead to data corruption or security vulnerabilities.

What is an off-by-one vulnerability in smart contract security auditing?

An off-by-one vulnerability in smart contract security auditing is a fence-post error in loop boundaries, array accesses, or threshold comparisons. It causes unexpected behavior by incorrectly processing array elements or inaccurately enforcing financial thresholds, leading to unintended inclusions or exclusions.

How do I fix array index calculation errors in Solidity?

To fix array index calculation errors in Solidity, apply remediation guidance that corrects loop boundary conditions and threshold comparisons. This ensures your smart contract correctly processes all elements in an array without unintended inclusions or exclusions.

Can I use automated analysis to check loop boundary conditions in smart contracts?

Yes, you can use automated analysis to check loop boundary conditions in smart contracts. Pattern matching analyzes Solidity code to identify common off-by-one mistakes in loops and array accesses, providing clear instructions on how to fix identified issues.

Why does my Solidity loop skip the last element in an array?

Your Solidity loop skips the last element in an array due to a boundary condition mismatch, commonly known as an off-by-one error. Analyzing the loop boundary conditions identifies this fence-post error so you can apply the correct remediation.