evm-token-decimals

evm-token-decimals is a skill for Claude Code, Codex from ufy2024/AuC. It costs 44 tokens per session (1,030 once invoked), scanned A, original, MIT.

A guide for handling token decimal differences on EVM-compatible blockchains, networks that run Ethereum-style smart contracts. It covers balances, fiat values, bridged tokens, and chain-specific token data.

In plain words
What is it for?
Use it when building wallets, portfolio trackers, bots, dashboards, DeFi tools, or aggregators that read ERC-20 balances across chains.
Why use it?
It prevents silent calculation errors where balances or prices are wrong by factors of ten or more without producing an error.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit Use it when building wallets, portfolio trackers, bots, dashboards, DeFi tools, or aggregators that read ERC-20 balances across chains.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/ufy2024/auc/evm-token-decimals
View source ↗ ufy2024/AuC
About the project

AuC is a Python framework for running a single AI agent with an asynchronous, pluggable reasoning loop, language-model adapters, permission levels, and observable events. It is used to build coding and conversational agents with tools, security checks, web interfaces, background jobs, evaluations, and isolated execution. The catalogue entries are skills for extending its agent workflow.

ufy2024/AuC · 1,090 stars · on GitHub

Install

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.

Any agent
npx skills add ufy2024/AuC --skill evm-token-decimals
Clone the repo
git clone --depth 1 https://github.com/ufy2024/AuC

Made for: Claude Code, Codex.

Wrote 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.

agentmods badge for evm-token-decimals

README.md
[![agentmods](https://agentmods.dev/badge/skills/ufy2024/auc/evm-token-decimals.svg)](https://agentmods.dev/skills/ufy2024/auc/evm-token-decimals)
Your own site
<a href="https://agentmods.dev/skills/ufy2024/auc/evm-token-decimals"><img src="https://agentmods.dev/badge/skills/ufy2024/auc/evm-token-decimals.svg" alt="Measured on agentmods" height="20"></a>
Per session 44 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,030 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 1 finding, up to medium

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • medium Agent Snooping · line 21
    Skill enumerates or reads other installed skills. Access to other skills' SKILL.md files or the skills directory reveals prompt instructions, capabilities, and secrets that should be invisible to peer skills.
    Fix: Remove all code or instructions that list or read other skills' files or directories. Skills should operate independently; cross-skill access is a privilege escalation.
How audits are shown
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00044 $0.01030
Opus 5 $0.00022 $0.00515
Sonnet 5 $0.00009 $0.00206
Haiku 4.5 $0.00004 $0.00103

Measured 5d ago against content hash 9ebf0e5ec001, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

evm-token-decimals 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.

Origin

Copies of this mod

3 near-identical copies found in the catalogue:

auc/skill_library/bundled/evm-token-decimals/SKILL.md · 151 lines

How it starts

The opening of the file, as written. The whole thing — 151 lines — stays where its author put it; the contents beside it link to each section on GitHub.

EVM Token Decimals

Silent decimal mismatches are one of the easiest ways to ship balances or USD values that are off by orders of magnitude without throwing an error.

When to Use

  • Reading ERC-20 balances in Python, TypeScript, or Solidity
  • Calculating fiat values from on-chain balances
  • Comparing token amounts across multiple EVM chains
  • Handling bridged assets
  • Building portfolio trackers, bots, or aggregators

How It Works

Never assume stablecoins use the same decimals everywhere. Query decimals() at runtime, cache by (chain_id, token_address), and use decimal-safe math for value calculations.

Examples

Query decimals at runtime

from decimal import Decimal
from web3 import Web3

ERC20_ABI = [
    {"name": "decimals", "type": "function", "inputs": [],
     "outputs": [{"type": "uint8"}], "stateMutability": "view"},
    {"name": "balanceOf", "type": "function",
     "inputs": [{"name": "account", "type": "address"}],
     "outputs": [{"type": "uint256"}], "stateMutability": "view"},
]

def get_token_balance(w3: Web3, token_address: str, wallet: str) -> Decimal:
    contract = w3.eth.contract(
        address=Web3.to_checksum_address(token_address),
        abi=ERC20_ABI,
    )
    decimals = contract.functions.decimals().call()
    raw = contract.functions.balanceOf(Web3.to_checksum_address(wallet)).call()
    return Decimal(raw) / Decimal(10 ** decimals)

Do not hardcode 1_000_000 because a symbol usually has 6 decimals somewhere else.

Cache by chain and token

from functools import lru_cache

@lru_cache(maxsize=512)
def get_decimals(chain_id: int, token_address: str) -> int:
    w3 = get_web3_for_chain(chain_id)
    contract = w3.eth.contract(
        address=Web3.to_checksum_address(token_address),
        abi=ERC20_ABI,
    )
    return contract.functions.decimals().call()

Handle odd tokens defensively

try:
    decimals = contract.functions.decimals().call()
except Exception:
    logging.warning(
        "decimals() reverted on %s (chain %s), defaulting to 18",
        token_address,
        chain_id,
    )
    decimals = 18

Read the full file on GitHub · 151 lines

Changes

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.

  1. 5d ago First seen · 151 lines · 44 tokens per session scan A 9ebf0e5ec001

Subscribe to this mod's changes

evm-token-decimals is a skill published in the GitHub repository ufy2024/AuC (1,090 stars, last pushed 1mo ago), licensed MIT. It adds 44 tokens to every session and 1,030 once invoked, about $0.0002 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 2026-09-03.