FIX Protocol Tag=Value Pair Regex for PHP

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching fix protocol tag=value pair, ported and verified for PHP. 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 PHP project — whether you're validating in a Laravel validator, a WordPress plugin, or a standalone PHP script.

Php Implementation

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

define('FIX_PROTOCOL_TAGVALUE_PAIR_PATTERN', '/^[0-9]+=[^\x01\s]+$/');

function validate_fix_protocol_tagvalue_pair(string $input): bool {
    return (bool) preg_match(FIX_PROTOCOL_TAGVALUE_PAIR_PATTERN, $input);
}

// Example
var_dump(validate_fix_protocol_tagvalue_pair("35=D")); // bool(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 PHP developers because especially relevant in PHP where PCRE backtracking limits can trigger silent failures on malicious input. 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.