How to Build a MEV-Protected Swap Service in TypeScript

Sandwich bots extracted $289 million from Ethereum swaps in 2025 alone, accounting for over 51% of all MEV activity on the network ( ScienceDirect, 2025 ). Every unprotected swap is a potential victim. If you are building a swap service, wallet, or trading bot, MEV protection is not optional. This guide walks you through building a MEV-protected token swap service in TypeScript. You will learn what MEV is, how sandwich attacks work, and how to use pre-trade validation, slippage enforcement, and private transaction submission to protect every swap. What You Will Need Node.js 18+ or Bun runtime TypeScript configured in your project A wallet library: viem or ethers.js v6 Access to a swap API (we will use swapapi.dev -- free, no API key, 46 chains) A private RPC endpoint (Flashbots Protect, MEV Blocker, or similar) Step 1: Understand MEV and Why Your Swaps Are Vulnerable Maximal Extractable Value (MEV) is the profit that block producers and searchers can extract by reordering, inserting, o