FIX Protocol Tag=Value Pair Regex for JavaScript

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching fix protocol tag=value pair, 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

// FIX Protocol Tag=Value Pair
// ReDoS-safe | RegexVault — Finance > Securities & Trading

const fixProtocolTagvaluePairRegex = /^[0-9]+=[^\x01\s]+$/;

function validateFixProtocolTagvaluePair(input: string): boolean {
  return fixProtocolTagvaluePairRegex.test(input);
}

// Example
console.log(validateFixProtocolTagvaluePair("35=D")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Securities & Trading category and carries a ReDoS-safe certification. 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

FIX protocol separates fields with SOH (\x01, ASCII 001). This pattern matches a single field — strip the SOH delimiter before matching individual pairs. Capture group 1: tag number, group 2: value. Tag 35 is MsgType.