YAML Formatter

About YAML Formatter

What is a YAML Formatter?

A YAML Formatter takes your YAML and turns it into a clean, consistently indented, easy-to-read file. YAML (YAML Ain't Markup Language) is a human-readable data serialization language that is widely used for configuration files, infrastructure as code, and data exchange.

How to use this tool

Type or paste your YAML into the editor and press Format. Comments stay where they are. The tool checks your YAML as you type: when something is wrong, it rings the exact spot, gives the line and column, and says what to fix. Lines that Format changed stay marked until you edit them, and Show before shows your text as it was.

Summarize YAML

The Result pane counts the documents, keys, lists and values in your YAML, and shows the nesting depth. Open Notes to see each top-level key and what it holds, next to its line.

Convert YAML to JSON

Open the JSON tab in the Result header to see your YAML as JSON. Copy and Download then take the JSON. A file with several documents becomes a JSON array. To go the other way, use JSON to YAML.

Customization

Open Options to set the indent, whether short lists and maps in brackets stay on one line or always go on separate lines, double or single quotes, the line width, and sorting keys A to Z. The tool remembers your choices.

YAML vs JSON

YAML and JSON are both data serialization formats, but they serve slightly different purposes. JSON is more compact and widely used for APIs and data exchange, while YAML is easier to read and common in configuration files. Since YAML 1.2, valid JSON is also valid YAML, but YAML adds comments, anchors, aliases, and multi-line strings.

Common YAML syntax errors

Incorrect indentation

YAML uses indentation to define structure. Mixing tabs and spaces, or using different indents at the same level, is the most common source of YAML errors. Always use spaces, never tabs, and keep the same number of spaces per level.

server:
  host: example.com
   port: 8080

server:
  host: example.com
  port: 8080

Missing colons or spaces

A key and its value need a colon followed by a space: key: value. Without the space, key:value is read as one plain text value, not a key.

Unquoted special characters

Values that start with special characters such as {, [, *, & or @, or that contain : or #, must be quoted. Without quotes, the parser reads these characters as structure or as a comment.

message: Error: disk full
channel: @ops

message: "Error: disk full"
channel: "@ops"

YAML best practices

• Use 2 spaces for indentation, the most common convention in the YAML ecosystem.
• Never use tabs for indentation. The YAML specification forbids them.
• Quote values that could be read as another type, such as "true", "3.14" or "null", when you mean them as text.
• Use comments (#) to document complex configurations.
• Use anchors and aliases to avoid repetition in large files.
• Validate your YAML before you deploy, to catch errors early.

YAML

YAML (YAML Ain't Markup Language) is a human-readable data serialization language. It was first proposed by Clark Evans in 2001 and has become one of the most popular formats for configuration files. YAML is designed to be easy to read and write, which makes it a natural choice for configuration management, infrastructure as code, and data exchange between systems.

• The conventional extensions for YAML files are .yaml and .yml. Both are widely used, and .yaml is the officially recommended one.
• The MIME type for YAML is application/yaml, as registered in RFC 9512.

Why use YAML?

YAML is the standard for configuration in the DevOps world. Its clean, indentation-based syntax makes complex configuration readable at a glance, which matters when you manage infrastructure and deployment pipelines.

• YAML is easier to read than JSON or XML, with very little syntax.
• YAML supports comments, so you can document configuration choices inline.
• YAML supports anchors, aliases, and merge keys to reduce repetition in large configuration files.
• Valid JSON is also valid YAML, so you can use JSON syntax inside YAML files when needed.

Common YAML use cases

• Docker Compose. Define multi-container applications with services, networks, and volumes in docker-compose.yml.
• Kubernetes. Declare deployments, services, config maps, and other resources as YAML manifests.
• GitHub Actions. Define CI/CD workflows in .github/workflows/.
• Ansible. Write playbooks, roles, and inventory files to automate server setup and configuration.
• CI/CD pipelines. Configure build and deployment pipelines in GitLab CI, CircleCI, and other platforms.
• Application config. Many frameworks and tools, such as Spring Boot, MkDocs, Prettier and ESLint, accept YAML configuration files.

YAML 1.2 specification

The current version of YAML is YAML 1.2 (revision 1.2.2), released in October 2021. YAML 1.2 aligned YAML with JSON, removed several surprising implicit types (such as reading unquoted yes and no as booleans), and made the data model clearer. YAML 1.2 is the recommended version for new projects.