contracts-mev-sandwich

contracts-mev-sandwich is a skill for Claude Code from PurpleAILAB/Decepticon. It costs 58 tokens per session (1,180 once invoked), scanned A, original, Apache-2.0.

A Web3 security playbook for sandwich attacks, in which a trader's decentralized-exchange swap is placed between an attacker’s buy and sell transactions.

In plain words
What is it for?
It is for monitoring pending transactions, checking swap types and slippage limits, estimating profitability, and constructing private transaction bundles.
Why use it?
It helps identify swaps whose permitted price movement makes them profitable to front-run and back-run.

Skill for Claude Code

Written for Claude Code: allowed-tools in frontmatter.

Good fit It is for monitoring pending transactions, checking swap types and slippage limits, estimating profitability, and constructing private transaction bundles.

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Install with agentmods
npx agentmods add skills/purpleailab/decepticon/mev-sandwich
About the project

Decepticon is an autonomous red-team agent that coordinates AI agents, security tools, sandboxes, and supporting services for authorized cybersecurity assessments. Security researchers and red teams can run it through its Docker stack, cloud service, command-line interface, or Python SDK, with the catalogue entries representing its available skills.

PurpleAILAB/Decepticon · 5,491 stars · on GitHub · decepticon.red

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 PurpleAILAB/Decepticon --skill mev-sandwich
Clone the repo
git clone --depth 1 https://github.com/PurpleAILAB/Decepticon

Made for: Claude Code.

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 contracts-mev-sandwich

README.md
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Your own site
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Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for contracts-mev-sandwich

Your own site · 80×15
<a href="https://agentmods.dev/skills/purpleailab/decepticon/mev-sandwich"><img src="https://agentmods.dev/badge/skills/purpleailab/decepticon/mev-sandwich.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 58 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,180 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 pass 7 Sept 2026
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 $0.00058 $0.01180
Opus 5 $0.00029 $0.00590
Sonnet 5 $0.00012 $0.00236
Haiku 4.5 $0.00006 $0.00118

Measured 9d ago against content hash 501593393149, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

contracts-mev-sandwich 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 9d 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

1 near-identical copy found in the catalogue:

packages/decepticon/decepticon/skills/standard/contracts/mev-sandwich/SKILL.md · 117 lines

How it starts

The opening of the file, as written. The whole thing — 117 lines — stays where its author put it; the contents beside it link to each section on GitHub.

MEV Sandwich Attack

You observe a victim's DEX swap in the mempool. Sandwich it: buy the same token before the victim (pushing price up), let the victim swap at a worse price, then sell after them.

Detect a sandwichable swap

# Stream pending transactions
from web3 import Web3
w3 = Web3(Web3.HTTPProvider("https://eth.merkle.io"))
# Or: subscribe to alchemy/blocknative streams

# Filter for Uniswap V2 swapExactTokensForTokens or V3 exactInputSingle
# Look at the swap amount + slippage tolerance (deadline + minAmountOut)
# Sandwichable when: swap_amount * slippage > sandwich_gas_cost * 2

Math: profitable when victim's slippage tolerance exceeds your gas cost. Typical threshold for ETH/USDC swaps: victim swap >$10k with >1% slippage.

Construct the sandwich bundle

// Bundle: 3 tx in same block, in order
// 1. attacker_tx_1: swap baseToken -> token (push price UP)
// 2. victim_tx:     swap baseToken -> token (worse price now)
// 3. attacker_tx_2: swap token -> baseToken (sell back at higher price)
// Flashbots bundle (Ethereum mainnet — others have similar private RPCs)
const ethers = require("ethers");
const { FlashbotsBundleProvider } = require("@flashbots/ethers-provider-bundle");

const provider = new ethers.providers.JsonRpcProvider(process.env.RPC);
const wallet = new ethers.Wallet(process.env.PK, provider);
const fb = await FlashbotsBundleProvider.create(provider, wallet, "https://relay.flashbots.net");

const blockNumber = await provider.getBlockNumber();
const bundle = [
  { signer: wallet, transaction: attackerTx1 },  // front-run
  { signedTransaction: rawVictimTx },             // victim from mempool
  { signer: wallet, transaction: attackerTx2 },  // back-run
];

const signedBundle = await fb.signBundle(bundle);
await fb.sendRawBundle(signedBundle, blockNumber + 1);

JIT (Just-In-Time) liquidity sandwich

Uniswap V3 concentrated liquidity lets you provide liquidity in a tight range for one block:

Read the full file on GitHub · 117 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. 9d ago First seen · 117 lines · 58 tokens per session scan A 501593393149

Subscribe to this mod's changes

contracts-mev-sandwich is a skill published in the GitHub repository PurpleAILAB/Decepticon (5,491 stars, last pushed 13d ago), licensed Apache-2.0. It adds 58 tokens to every session and 1,180 once invoked, about $0.0003 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.