Claude Skills Guide

Claude Code Skill Invalid YAML Syntax Error How to Debug

When you build custom Claude skills, the YAML front matter at the top of your skill file must be valid A single typo in this section breaks the entire skill, often leaving you with a cryptic error message. This guide walks through common YAML syntax errors in Claude skills and shows you exactly how to debug them.

Why YAML Front Matter Matters in Claude Skills

Every Claude skill file starts with a YAML block wrapped between triple dashes. This section defines metadata that Jekyll (the static site generator) and the skill loading system use to process your skill correctly. The front matter looks like this:

---
layout: default
title: "My Custom Skill"
description: "A skill that does something useful"
date: 2026-03-14
author: yourname
---

When this YAML is invalid, Claude cannot load your skill, and you’ll encounter errors that seem confusing at first. The good news is that YAML errors follow predictable patterns, and once you know what to look for, debugging becomes straightforward.

Common YAML Syntax Errors in Claude Skills

Indentation Problems

YAML relies on consistent indentation using spaces, not tabs. Most errors stem from mixing tabs with spaces or using incorrect indentation levels. For example, this code is broken:

---
layout: default
title: "Broken Skill"
  description: "This will fail"
---

The description line uses two extra spaces, which YAML interprets as a nested element. Remove the extra spaces:

---
layout: default
title: "Fixed Skill"
description: "This now works"
---

Missing Colons or Quotes

YAML requires colons after keys, and values containing special characters need quotes. Consider this broken example:

---
layout: default
title: My Skill with: Colon
description: A skill description with "quotes"
---

The title value contains a colon, which YAML reads as a new key-value pair. Wrap it in quotes:

---
layout: default
title: "My Skill with: Colon"
description: "A skill description with \"quotes\""
---

Trailing Whitespace and Hidden Characters

Sometimes your YAML looks correct but contains invisible characters. This happens when copying from PDFs, word processors, or websites that insert smart quotes or non-breaking spaces. Use a plain text editor to verify your file contains only standard ASCII characters.

Malformed Lists and Arrays

If your front matter includes tags or categories as a list, use the correct YAML array syntax:

---
layout: default
title: "Skill with Tags"
tags: [claude-code, debugging, yaml]
categories: [troubleshooting]
---

Avoid this common mistake:

---
layout: default
title: "Broken Tags"
tags: claude-code, debugging, yaml
---

How to Debug YAML Errors Step by Step

Step 1: Validate Your YAML

Before troubleshooting further, run your YAML through a validator. The yamllint tool catches most issues:

yamllint your-skill-file.md

If you don’t have yamllint installed, use an online validator like YAMLlint.com. Paste your front matter (just the part between the --- lines) to check for syntax errors.

Step 2: Check the Error Message

When Claude encounters a broken skill, the error message usually indicates the line number where parsing failed. Look at your skill file around that line number. Common error messages include:

Step 3: Isolate the Problem

If your front matter is long, comment out sections temporarily to isolate which part causes the error. In YAML, lines starting with # are comments:

---
layout: default
# title: "Temporarily commented"
# description: "Testing"
date: 2026-03-14
---

Step 4: Verify Special Characters

Certain characters break YAML parsing unless properly escaped. These include:

Let me show you actual front matter from working skills to illustrate correct formatting.

A simple skill like one for PDF manipulation uses minimal front matter:

---
layout: default
title: "PDF Manipulation Skill"
description: "Work with PDF files using Python libraries"
date: 2026-01-15
author: "Claude Skills Guide"
---

A more complex skill with multiple tags, like a frontend design skill, might include:

---
layout: default
title: "Frontend Design Assistant"
description: "Generate responsive layouts, components, and styling with Tailwind CSS"
date: 2026-02-20
author: "Claude Skills Guide"
tags: [frontend, design, tailwind, css, ui]
---

The TDD (Test-Driven Development) skill uses front matter without issues:

---
layout: default
title: "TDD Companion"
description: "Write tests first, then implement features"
date: 2026-02-10
author: "Claude Skills Guide"
---

Preventing YAML Errors in the Future

Use a Linter in Your Editor

Configure your text editor to highlight YAML syntax errors. VS Code with the YAML extension, JetBrains IDEs, and Sublime Text all provide real-time validation. Enable format-on-save to catch issues automatically.

Keep Front Matter Minimal

Only include fields you actually need. Each additional line is another opportunity for errors. Stick to the basics: layout, title, description, date, and author.

Use Templates

When creating new skills, start from a proven template rather than writing front matter from scratch. This is especially helpful when working with complex skills like the supermemory skill or the canvas-design skill that might require additional metadata.

Troubleshooting Persistent Issues

If you have validated your YAML repeatedly and still see errors, check for these less obvious problems:

  1. Encoding issues — Save your file as UTF-8 without BOM
  2. Line endings — Use Unix-style line endings (LF), not Windows (CRLF)
  3. Invisible Unicode — Copy-pasting from some websites introduces zero-width characters
  4. Cache problems — Jekyll sometimes caches invalid builds; run jekyll clean or delete the _site directory

Summary

YAML syntax errors in Claude skills are frustrating but avoidable. Remember these key points: use consistent space indentation, quote values with special characters, validate with tools like yamllint, and keep your front matter minimal. Most errors come from indentation mistakes, unquoted colons, or hidden characters from copy-pasting.

When debugging, start by validating your YAML, then isolate problematic sections, and finally check for encoding issues. With practice, you’ll spot and fix these errors in seconds rather than minutes.

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