Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/zaryab2000/decipher-gas-optimizoor/custom-errorsnpx skills add zaryab2000/decipher-gas-optimizoor --skill custom-errorsgit clone --depth 1 https://github.com/zaryab2000/decipher-gas-optimizoorWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/zaryab2000/decipher-gas-optimizoor/custom-errors)<a href="https://agentmods.dev/skills/zaryab2000/decipher-gas-optimizoor/custom-errors"><img src="https://agentmods.dev/badge/skills/zaryab2000/decipher-gas-optimizoor/custom-errors.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00097 | $0.01284 |
| Opus 5 | $0.00048 | $0.00642 |
| Sonnet 5 | $0.00019 | $0.00257 |
| Haiku 4.5 | $0.00010 | $0.00128 |
Grade A, and why
custom-errors scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 5d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 126 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Purpose
Convert every string-based revert in a Solidity contract to a custom error. Custom errors (introduced in Solidity 0.8.4) use a 4-byte selector instead of a string, reducing bytecode size and runtime revert cost by ~15–50 gas per revert path.
When to Use This Skill
Use when:
- Claude is writing any
require(condition, "string")statement - Claude is writing any
revert("string literal")statement - The user asks Claude to review revert logic in a contract
- Claude is about to finalize any function that contains error conditions
- A contract imports OpenZeppelin or other libraries that still use string reverts
Fire on every require(cond, "string") or revert("string") without exception.
When NOT to Use This Skill
Do NOT use for:
require(condition)with no message — no string to remove, nothing to convertrevert CustomError()— already a custom error, review only for CE-003 context- Contracts targeting Solidity < 0.8.4 — custom errors did not exist before 0.8.4
- Third-party library code you do not control (flag but do not modify)
- String-based reverts in test files where human-readable messages aid test output
Platform Detection
This skill applies when the following markers are present:
File extensions: *.sol
Project markers: foundry.toml or hardhat.config.ts in project root
Language markers:
pragma solidity ^0.8.x;(must be 0.8.4 or higher)contract,library, orinterfacedeclarationsrequire(,revert(usage in function bodies
Do not apply to Vyper (.vy) or non-EVM languages.
Quick Reference
| Pattern | Fix | Gas Saving |
|---|---|---|
require(cond, "string") |
if (!cond) revert CustomError() |
~15–50 gas runtime + bytecode reduction |
revert("string") |
revert CustomError() |
~15–50 gas runtime + bytecode reduction |
revert CustomError() with no context |
Add typed params if useful | Better debugging, minimal cost |
Decision rule: If a quote mark appears inside a require() or revert(), this
skill fires. No exceptions.
What ships with it
3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 5d ago First seen · 126 lines · 97 tokens per session scan A 7994eeebffca
custom-errors is a skill published in the GitHub repository zaryab2000/decipher-gas-optimizoor (7 stars, last pushed 6mo ago), licensed MIT. It adds 97 tokens to every session and 1,284 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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