Fix: Failed to Parse Markdown Frontmatter in Astro - Astro Error Fix

What Causes This Error?

This error occurs when the frontmatter in a Markdown file has invalid YAML syntax. Frontmatter must be valid YAML between --- delimiters.

The Problem

---
title: My Post
date: January 15 2024   # ❌ Invalid date format
tags: [one, two         # ❌ Missing closing bracket
description: This has: a colon  # ❌ Unquoted colon
---

The Fix

Use Valid YAML Syntax

---
title: "My Post"
date: 2024-01-15
tags: [one, two]
description: "This has: a colon"
---

Common Scenarios

Unquoted Special Characters

---
# ❌ Colons need quoting
title: Part 1: The Beginning

# ✅ Quote the string
title: "Part 1: The Beginning"
---

Date Formats

---
# ❌ Invalid date
date: January 15, 2024

# ✅ Valid ISO format
date: 2024-01-15
date: 2024-01-15T10:30:00Z
---

Arrays

---
# ❌ Broken array
tags: [javascript, typescript

# ✅ Valid array
tags: [javascript, typescript]
# Or multiline
tags:
  - javascript
  - typescript
---

Indentation Issues

---
# ❌ Wrong indentation
author:
name: John    # Missing indent
email: john@example.com

# ✅ Proper indentation
author:
  name: John
  email: john@example.com
---

Boolean Values

---
# ❌ String instead of boolean
draft: "true"
featured: yes

# ✅ YAML booleans
featured: true
---

Multiline Strings

---
# ✅ Literal block (preserves newlines)
description: |
  This is a long description
  that spans multiple lines.

# ✅ Folded block (joins lines)
summary: >
  This will become
  one single line.
---

Escaping Quotes

---
# ❌ Unescaped quotes
title: He said "Hello"

# ✅ Escaped or different quotes
title: 'He said "Hello"'
title: "He said \"Hello\""
---

Tab Characters

---
# ❌ Tab characters (invisible but cause errors)
title:	"My Post"    # Tab before title

# ✅ Use spaces only
title: "My Post"     # Spaces
---

Numbers vs Strings

---
# These are numbers
count: 123
price: 19.99

# These are strings
zipcode: "00123"    # Leading zero preserved
phone: "+1-555-1234"
---

Validating Frontmatter

# Use a YAML linter
echo "---
title: My Post
tags: [a, b
---" | yq e .

# Online validators
# https://www.yamllint.com/

VS Code Settings

// .vscode/settings.json
{
  "yaml.validate": true,
  "yaml.schemas": {
    "./schema.json": "src/content/**/*.md"
  }
}

Checking Error Location

Error: Failed to parse Markdown frontmatter
at src/content/blog/my-post.md
YAMLException: bad indentation of a mapping entry at line 5

→ Check line 5 of the frontmatter

Quick Checklist

Quote strings with special characters (: # [ ] { })
Use spaces, not tabs
Arrays need matching brackets
Dates in ISO format (YYYY-MM-DD)
Booleans are true/false (not quoted)
Check indentation for nested objects