Best practices for quoting YAML frontmatter values

Understanding when to quote values in YAML frontmatter is crucial for maintaining robust and readable technical documentation. While YAML's flexibility allows for unquoted strings in many cases, certain scenarios require careful consideration of quoting to prevent parsing errors and ensure consistent behaviour across different systems.

The problem

YAML parsers handle unquoted strings differently from quoted ones. Unquoted strings undergo implicit typing, where the parser attempts to determine the appropriate data type based on the content. This behaviour can lead to unexpected results when working with frontmatter in static site generators and documentation systems.

When quoting is required

Certain value types must always be quoted to ensure proper parsing:

Values containing special characters:

title: "Using CI/CD: A comprehensive guide"
description: "Learn about arrays [1, 2, 3] in Python"

Values starting with numeric characters:

title: "5 essential Git commands"
subtitle: "2025 DevOps trends"

Multi-line strings requiring exact whitespace:

description: "This tutorial covers:
  - Basic concepts
  - Advanced techniques"

When to skip quotes

Simple alphanumeric strings without special characters don't require quotes:

category: Programming
author: Alice Smith
status: draft

Best practices for technical documentation

When working with technical documentation, follow these guidelines:

1. Always quote titles containing punctuation or special characters
2. Quote description fields containing colons, brackets, or line breaks
3. Leave simple category and tag values unquoted unless they contain special characters
4. Use consistent quoting style (single or double quotes) throughout your project

Examples from production

Consider this real-world frontmatter example:

---
title: "Building REST APIs: best practices"
category: Web Development
tags: ["api", "rest", "best-practices"]
description: "Learn how to design and implement RESTful APIs using industry standards."
series:
  name: "API development"
  part: 1
---

Impact on parsing and maintenance

Proper quoting practices affect both parser behaviour and long-term maintenance:

• Consistent quoting reduces the risk of parsing errors when content is processed
• Clear guidelines simplify the contribution process for new team members
• Standardised practices make automated frontmatter validation more reliable

Conclusion

While YAML offers flexibility in value quoting, establishing clear guidelines improves documentation maintainability and prevents parsing issues. Quote values containing special characters or requiring exact formatting, but keep simple strings unquoted for better readability.

Regularly review your documentation's frontmatter for compliance with these guidelines, especially when implementing automated building and testing processes.