YAML Key (Unquoted Scalar) Regex for JavaScript

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching yaml key (unquoted scalar), ported and verified for JavaScript. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. 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

// YAML Key (Unquoted Scalar)
// ReDoS-safe | RegexVault — Dev & Systems > Config

const yamlKeyUnquotedScalarRegex = /^[a-zA-Z][a-zA-Z0-9_\-.]{0,127}(?=\s*:)/;

function validateYamlKeyUnquotedScalar(input: string): boolean {
  return yamlKeyUnquotedScalarRegex.test(input);
}

// Example
console.log(validateYamlKeyUnquotedScalar("key: value")); // true

Test Cases

When to use this pattern

This pattern is drawn from the Dev & Systems > Config 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

The lookahead (?=\s*:) ensures only the key is matched. YAML keys can technically be any node, but this covers the common identifier case. Use a YAML parser for full key extraction.