Bitcoin Address (Legacy P2PKH — starts with 1) Regex for JavaScript

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching bitcoin address (legacy p2pkh — starts with 1), ported and verified for JavaScript. Financial data validation has zero tolerance for false negatives — a missed invalid entry can corrupt downstream calculations. The snippet below is ready to drop into your JavaScript project — whether you're validating in an Express middleware, a Next.js API route, or a client-side form.

Javascript Implementation

// Bitcoin Address (Legacy P2PKH — starts with 1)
// ReDoS-checked | RegexVault — Finance > Crypto

const bitcoinAddressLegacyP2pkhStartsWith1Regex = /^1[a-km-zA-NP-Z1-9]{25,34}$/;

function validateBitcoinAddressLegacyP2pkhStartsWith1(input: string): boolean {
  return bitcoinAddressLegacyP2pkhStartsWith1Regex.test(input);
}

// Example
console.log(validateBitcoinAddressLegacyP2pkhStartsWith1("1A1zP1eP5QGefi2DMPTfTL5SLmv7Divf")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Crypto category and has been checked for ReDoS risk. That matters for JavaScript developers because especially critical in long-running Node.js event loops where a ReDoS vulnerability can block the entire process. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

P2PKH addresses start with 1. Base58Check encoding (excludes 0, O, I, l to avoid confusion). Length is 25-34 chars. The address encodes a hash of the public key — validate the checksum with actual Base58Check decoding.