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Developer Tools

YAML Validator

Validate YAML syntax with detailed error messages, line highlighting, and auto-formatting.

Paste YAML content above to validate

The validator checks syntax and can convert valid YAML to JSON

YAML Tips

  • Use spaces for indentation (tabs are not allowed in YAML)
  • Quote strings containing special characters: : # [ ] {} & * ! | > ' " %
  • Boolean values: true/false, yes/no, on/off
  • Null values: null, ~, or empty value
  • Comments start with # and extend to end of line
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Frequently Asked Questions

What is YAML?
YAML (YAML Ain't Markup Language) is a human-readable data serialization format commonly used for configuration files. It uses indentation to represent structure, making it more readable than JSON or XML for configuration purposes. YAML is used by Docker Compose, Kubernetes, Ansible, GitHub Actions, CI/CD pipelines, and many other tools.
What are common YAML syntax errors?
The most common YAML errors are: incorrect indentation (YAML requires consistent spaces, not tabs), missing colons after keys, improper quoting of strings containing special characters, duplicate keys in the same mapping, and incorrect list syntax. Our validator identifies these errors with specific line numbers for easy debugging.
Can YAML be converted to JSON?
Yes, YAML is a superset of JSON, meaning any JSON document is also valid YAML. Converting YAML to JSON is straightforward because both formats represent the same data structures (objects, arrays, strings, numbers, booleans, null). Our tool performs this conversion instantly, producing clean formatted JSON from your YAML input.
What are YAML anchors and aliases?
Anchors (&name) and aliases (*name) allow you to reuse content within a YAML document. An anchor marks a value with a name, and aliases reference that value elsewhere. This is useful for avoiding repetition in configuration files. For example, you can define a set of default settings with an anchor and reference it across multiple services.
Should I use tabs or spaces in YAML?
YAML requires spaces for indentation. Tabs are not allowed and will cause a parse error. The most common convention is 2 spaces per indentation level, though some projects use 4 spaces. Whatever you choose, be consistent throughout the file. Configure your editor to insert spaces when you press the Tab key in YAML files.
What is the difference between YAML and JSON?
YAML is a superset of JSON with additional features. YAML supports comments (JSON does not), uses indentation instead of braces, allows unquoted strings, supports anchors/aliases for content reuse, and has multi-line string syntax. JSON is more widely supported in APIs and programming languages, while YAML is preferred for configuration files due to readability.
How does the YAML validator work?
Our YAML validator parses your input using a custom YAML parser that runs entirely in your browser. It checks for syntax errors including invalid indentation, malformed keys/values, duplicate keys, and incorrect structure. When errors are found, they are reported with line numbers so you can quickly locate and fix the issue.

How to Use the YAML Validator

YAML configuration files are used by Docker Compose, Kubernetes, GitHub Actions, Ansible, and countless other tools. A single indentation error can prevent your entire configuration from working. Our YAML validator catches syntax errors instantly and shows you exactly where they occur with line number references.

Step 1: Paste your YAML. Copy your YAML configuration and paste it into the input area. The validator accepts any YAML content including multi-document YAML (separated by ---), anchors and aliases, and complex nested structures.

Step 2: View validation results. The validator immediately parses your YAML and reports either success or error details. Errors include the specific line number and a description of what went wrong, making it easy to locate and fix the issue in your original file.

Step 3: Convert to JSON. Valid YAML can be converted to JSON with one click. This is useful when you need to use the same data in a JSON-based tool, API, or programming language. The JSON output is properly formatted with 2-space indentation.

Step 4: Minify if needed. Reduce your YAML to a compact format by removing unnecessary whitespace and comments. While rarely needed for configuration files, minified YAML can be useful for data transmission or storage optimization.

Understanding YAML Syntax

YAML uses indentation and simple punctuation to represent data structures. Mappings (key-value pairs) are written as key: value. Lists use dash prefixes (- item). Nested structures are created with indentation. Comments start with # and extend to the end of the line. Strings can be unquoted, single-quoted, or double-quoted depending on their content.

The indentation rules in YAML are strict but simple. Use spaces only (never tabs). All items at the same level must use the same number of spaces. Child items must be indented more than their parent. The number of spaces per level is flexible (1, 2, 4, etc.) but must be consistent within each scope.

YAML supports multiple data types natively. Strings can be unquoted, single-quoted (no escape processing), or double-quoted (supports escape sequences like \n). Numbers (integers and floats) are recognized automatically. Boolean values include true/false, yes/no, and on/off. Null is represented by null or ~. Dates in ISO 8601 format are recognized as date objects.

YAML in Modern DevOps

Docker Compose. Docker Compose uses YAML to define multi-container application stacks. The docker-compose.yml file specifies services, networks, volumes, and their configurations. Even small syntax errors in this file can prevent containers from starting, making validation essential before deployment.

Kubernetes. Kubernetes manifests are YAML files that describe desired state for pods, deployments, services, and other resources. Kubernetes YAML files can be complex with multiple nested objects and cross-references. Validating syntax before applying manifests prevents deployment failures.

CI/CD Pipelines. GitHub Actions, GitLab CI, CircleCI, and other CI/CD platforms use YAML for pipeline configuration. These files define build steps, deployment procedures, and automation workflows. A YAML syntax error in a CI configuration can block your entire development pipeline.

Why Use Our YAML Validator?

Instant error detection. Paste your YAML and get immediate feedback on syntax errors with specific line numbers. No need to attempt deployment or run a command-line tool to discover configuration errors. Catch issues before they cause problems in production.

YAML to JSON conversion. Convert between YAML and JSON formats instantly. This is valuable when migrating configurations, working with APIs that expect JSON, or debugging data structure issues by viewing the same data in a different format.

No installation required. Validate YAML directly in your browser without installing any tools, CLIs, or extensions. The validator runs entirely client-side, keeping your configuration data private and secure. Works on any device with a modern web browser.

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