YAML Formatter & Validator
Format and validate YAML, convert YAML to JSON, inspect nested structure and catch syntax errors using reliable YAML parsing directly in your browser.
Format, Validate or Convert YAML
Beautify YAML, validate its syntax or convert the parsed structure into JSON.
Shortcut: Ctrl/Cmd + Enter to process YAML
YAML Document Overview
Structural information is calculated from the parsed YAML data.
Operation
Format
Indentation
2 Spaces
Top-Level Type
—
Maximum Depth
—
YAML Structure Statistics
See how mappings, sequences and scalar values make up the document.
Mappings
—
Sequences
—
Scalars
—
Total Nodes
—
Nesting Depth
—
Scalar Value Types
YAML can interpret values as several different data types rather than treating everything as text.
Strings
—
Integers
—
Floats
—
Booleans
—
Nulls
—
All Scalars
—
Document Size
Compare the original document with its formatted or converted output.
Input
0
Lines
0
Characters
0
Bytes
Output
0
Lines
0
Characters
0
Bytes
YAML Syntax Basics
YAML uses indentation and a small set of structural symbols to represent nested data.
Mapping
app:
name: SwiftVecto
debug: false
Mappings contain key-value pairs separated by colons.
Sequence
tools:
- json
- xml
- yaml
Dash-prefixed values form an ordered YAML sequence.
Nested Data
database:
connection:
host: 127.0.0.1
port: 3306
Indentation defines parent and child relationships.
Typed Values
enabled: true
attempts: 5
ratio: 1.25
fallback: null
YAML can parse booleans, numbers and null values as real data types.
Multiline YAML Strings
YAML provides two common block styles for multiline text.
Literal Block
description: |
First line
Second line
Third line
The
|
style generally preserves line breaks.
Folded Block
description: >
First line
Second line
Third line
The
>
style folds many line breaks into spaces according to YAML rules.
YAML Anchors & Aliases
Anchors can define reusable configuration that aliases reference elsewhere.
defaults: &defaults
timeout: 30
retries: 3
production:
<<: *defaults
debug: false
The
&defaults
anchor names a node, while
*defaults
references it.
YAML to JSON Example
YAML
app:
name: SwiftVecto
enabled: true
tools:
- json
- yaml
JSON
{
"app": {
"name": "SwiftVecto",
"enabled": true,
"tools": [
"json",
"yaml"
]
}
}
Where YAML Is Commonly Used
Docker Compose
Service, network, volume and container configuration.
GitHub Actions
CI/CD workflow triggers, jobs and steps.
Kubernetes
Deployments, services, configuration and resource definitions.
Ansible
Playbooks, variables and infrastructure automation.
Formatting May Remove YAML Comments
This formatter parses YAML into structured data and then serializes that data back into YAML.
Comments are generally not part of the parsed data structure used by
js-yaml
or Symfony YAML, so comments may disappear after formatting.
# Production configuration
app:
name: "SwiftVecto"
may be reformatted as:
app:
name: SwiftVecto
The underlying data is equivalent, but the comment and original quotation style are presentation details and are not guaranteed to survive.
Valid YAML Does Not Mean Valid Application Configuration
The validator checks YAML syntax. It does not currently validate application-specific schemas.
A YAML document can therefore parse correctly while still being invalid for Kubernetes, Docker Compose, GitHub Actions, Ansible or another system because of unsupported keys, missing properties or invalid values.
Use Spaces, Not Tabs, for YAML Indentation
YAML structure is defined through indentation, and indentation should use spaces.
The formatter outputs either two or four spaces per indentation level rather than tab characters.
Private Browser-Based YAML Processing
YAML formatting, validation and YAML-to-JSON conversion are performed directly inside your browser during normal interactive use.
- No YAML file upload is required.
- YAML content does not need to be sent to SwiftVecto's server.
- Browser parsing uses the installed js-yaml package.
- Structure and data-type statistics are calculated locally.
- Symfony YAML remains available as the server-side fallback implementation.
Continue with These Tools
Finished using YAML Formatter & Validator? Here are some related tools that people commonly use next to complete their workflow faster.
JSON Formatter & Validator
Format, beautify, minify and validate JSON online instantly. Detect invalid JSON, organise nested data and create clean, readable JSON directly in your browser.
XML Formatter & Validator
Format, minify and validate XML instantly. Beautify XML with configurable indentation, detect malformed markup and inspect document statistics directly in your browser.
SQL Formatter
Format, beautify and minify SQL with support for multiple database dialects, configurable indentation and keyword casing directly in your browser.
URL Encoder / Decoder
Encode or decode URLs and URL components instantly. Convert special characters to percent-encoded values, decode encoded text and work with URI components or form-style query data directly in your browser.
Regex Tester
Test JavaScript regular expressions online with live match highlighting, capturing groups, named groups, flags and replacement previews directly in your browser.
How to Format, Validate and Convert YAML
Use the SwiftVecto YAML Formatter & Validator to reformat YAML with consistent indentation, check YAML syntax and convert YAML into JSON. The tool uses a proper YAML parser rather than relying on manual text replacement.
Overview
YAML is a human-readable data serialization format widely used for configuration files, deployment manifests, CI/CD workflows, Docker Compose files, Kubernetes resources, Ansible playbooks and application settings. YAML relies heavily on indentation, which makes it readable but also means small whitespace errors can make a document invalid or change its structure. The SwiftVecto YAML Formatter & Validator parses the document into structured data before formatting or conversion. Format mode rebuilds the YAML using consistent indentation. Validate mode checks whether the YAML can be parsed successfully. YAML to JSON mode converts the parsed YAML structure into formatted JSON. The tool also calculates structural statistics including mapping counts, sequence counts, scalar counts and maximum nesting depth.
Benefits
How It Works
Paste or type YAML into the input editor.
Choose Format to parse and regenerate the YAML using consistent indentation.
Choose Validate to check whether the YAML can be parsed successfully.
Choose YAML to JSON to parse the YAML and serialize the resulting data structure as JSON.
The parser interprets mappings, sequences, strings, numbers, booleans and null values.
Nested structures are traversed to calculate document statistics.
Formatting only succeeds when the YAML is syntactically valid.
Validation checks parser correctness rather than validating application-specific configuration rules.
The server implementation uses Symfony YAML.
The browser implementation uses js-yaml for instant local processing.
How to Use This Tool
-
1Paste YAML into the input area.
-
2Choose Format YAML, Validate YAML or YAML to JSON.
-
3Select two-space or four-space indentation when formatting.
-
4Run the operation.
-
5Review any parser error if the document is invalid.
-
6Inspect the structural statistics when parsing succeeds.
-
7Copy the formatted YAML or JSON output when required.
-
8Use Load Sample to test the formatter quickly.
-
9Use Clear before starting another unrelated document.
Helpful Tips
- YAML indentation should use spaces rather than tabs.
- Be consistent with indentation depth throughout a document.
- A colon separates a mapping key from its value.
- A dash begins a sequence item when used in sequence context.
- Strings containing special YAML characters may need quotation marks.
- Values such as true, false and null may be interpreted as typed values rather than ordinary strings.
- Quote values when you need to guarantee that they remain strings.
- YAML supports nested mappings and sequences.
- YAML anchors and aliases can reduce repetition in configuration files.
- Block scalar syntax using | preserves line breaks.
- Folded scalar syntax using > folds line breaks into spaces according to YAML rules.
- Formatting YAML can normalize presentation even when the original source used a different style.
- Comments may not survive every parse-and-dump formatting workflow because comments are not always retained in the parsed data model.
- Validation in this tool checks YAML syntax, not whether the configuration is valid for Kubernetes, Docker Compose, GitHub Actions or another specific platform.
- Application-specific schema validation remains a separate concern.
Common Uses
Format a Docker Compose YAML file.
Validate a GitHub Actions workflow.
Convert YAML configuration into JSON.
Inspect nested Kubernetes resource data.
Find an indentation error in a configuration file.
Validate an Ansible playbook structure.
Beautify minified or inconsistently indented YAML.
Inspect the top-level type of a YAML document.
Count mappings and sequences in YAML.
Check whether a value is being parsed as a number or a string.
Format application configuration YAML.
Copy parsed YAML into debugging notes as JSON.
Worked Examples
The following examples demonstrate how this tool can be used in realistic scenarios.
Formatting Nested YAML
A YAML document containing application settings, database configuration and nested arrays can be parsed and rebuilt using consistent two-space or four-space indentation.
YAML Sequence
A list such as users followed by dash-prefixed items is parsed as a sequence rather than a mapping.
YAML Mapping
The structure name: SwiftVecto represents a mapping entry where name is the key and SwiftVecto is its value.
Boolean Value
The YAML value enabled: true is normally parsed as a boolean value rather than the string "true".
YAML to JSON
A YAML mapping containing application settings can be converted into a JSON object with equivalent nested structure.
Indentation Error
Incorrect indentation beneath a mapping or sequence can change the structure or produce a parser error. The validator reports the syntax failure rather than attempting to guess the intended layout.
Common Mistakes
Avoid these common mistakes to achieve the most accurate results.
- Using tabs for YAML indentation.
- Mixing inconsistent indentation widths.
- Misaligning sequence items.
- Forgetting the colon after a mapping key.
- Using a colon inside an unquoted string where it changes parsing meaning.
- Assuming every numeric-looking value will remain a string.
- Assuming true and false will always be treated as strings.
- Forgetting to quote values containing special syntax.
- Confusing YAML syntax validation with platform-specific schema validation.
- Assuming a syntactically valid Kubernetes YAML file is automatically a valid Kubernetes resource.
- Assuming a syntactically valid GitHub Actions file contains valid actions or workflow keys.
- Expecting every formatter to preserve comments.
- Expecting the exact original quoting style to survive a parse-and-dump formatting operation.
- Using duplicate mapping keys without understanding parser behaviour.
- Assuming YAML and JSON have identical syntax even though YAML can represent JSON-compatible structures using different notation.
Glossary
Definitions of the most important terms used by this tool.
YAML
A human-readable data serialization format commonly used for configuration and structured data.
Mapping
A YAML key-value structure similar to an object or associative array.
Sequence
An ordered YAML list commonly represented using dash-prefixed items.
Scalar
A single YAML value such as a string, number, boolean or null.
Indentation
Leading spaces used to define YAML hierarchy and nesting.
Anchor
A YAML feature that assigns a reusable name to a node using & syntax.
Alias
A YAML reference using * syntax that points to an anchored node.
Block Scalar
A multiline YAML string written using | or > syntax.
Literal Block
A multiline YAML scalar using | that generally preserves line breaks.
Folded Block
A multiline YAML scalar using > that generally folds line breaks according to YAML rules.
Parser
Software that reads YAML syntax and converts it into an in-memory structured data representation.
Serialization
The process of converting structured data into a textual format such as YAML or JSON.
Deserialization
The process of parsing YAML or another serialized format into structured data.
Schema Validation
Validation against application-specific structural rules beyond basic YAML syntax.
Frequently Asked Questions
What is a YAML formatter?
A YAML formatter parses YAML and outputs the resulting structure using consistent indentation and formatting.
What is a YAML validator?
A YAML validator checks whether the document follows YAML syntax closely enough to be parsed successfully.
Can this tool convert YAML to JSON?
Yes. Parsed YAML data can be serialized into formatted JSON.
Does YAML require spaces for indentation?
Yes. Tabs should not be used as indentation in YAML.
How many spaces should YAML use?
YAML does not mandate one universal indentation width, but two spaces are common and consistent indentation is essential.
What does a dash mean in YAML?
A dash commonly introduces an item in a YAML sequence.
What does a colon mean in YAML?
A colon commonly separates a mapping key from its value.
What is a YAML mapping?
A mapping is a set of key-value pairs similar to a JSON object or PHP associative array.
What is a YAML sequence?
A sequence is an ordered collection similar to a JSON array or PHP indexed array.
Can YAML contain comments?
Yes. YAML comments normally begin with #. However, comments may not survive a parser-based formatting operation because many parsers do not retain them in the data model.
What are YAML anchors?
Anchors allow a YAML node to be named and later referenced using an alias, reducing repeated configuration.
Can YAML represent multiline text?
Yes. YAML supports literal and folded block scalar styles using | and >.
Can valid YAML still be invalid for Kubernetes?
Yes. YAML syntax may be valid while the document still violates Kubernetes resource schemas or required fields.
Can valid YAML still be invalid for Docker Compose?
Yes. Syntax validation only confirms that YAML parses correctly. Docker Compose has its own allowed keys and configuration rules.
Does this tool validate GitHub Actions workflows?
It validates YAML syntax. It does not currently verify GitHub Actions-specific workflow keys, action names or platform rules.
Why did my quotes change after formatting?
Formatting works from the parsed data structure rather than preserving every stylistic choice in the original source. The serializer may therefore choose a different valid representation.
Why did my comments disappear after formatting?
Many YAML parsers treat comments as presentation metadata rather than part of the parsed data structure, so comments may not survive parse-and-dump formatting.
Can YAML contain JSON?
YAML is a superset of JSON in common YAML 1.2 usage, so JSON-style arrays and objects can often appear inside YAML documents.
Is YAML whitespace-sensitive?
Yes. Indentation determines hierarchy, making whitespace structurally significant.
Does SwiftVecto upload my YAML?
The interactive YAML Formatter & Validator is designed to perform normal formatting, validation and YAML-to-JSON conversion directly inside your browser.
Is the YAML Formatter & Validator free?
Yes. SwiftVecto provides this developer utility for formatting, validating and converting YAML.
Things to Know
- The server implementation uses Symfony YAML.
- The browser implementation should use js-yaml.
- Format mode reparses and serializes the YAML rather than merely adjusting whitespace.
- Comments may not be preserved during formatting.
- Original quoting style may change during formatting.
- Validation checks YAML syntax rather than platform-specific schemas.
- YAML to JSON operates on the parsed data structure.
- The tool should use spaces rather than tabs for generated YAML indentation.
- Normal interactive processing is intended to happen directly inside the browser.
Disclaimer
Syntactically valid YAML is not necessarily valid for Kubernetes, Docker Compose, GitHub Actions, Ansible or another application.
Parser-based formatting may change presentation details such as quoting style and may remove comments.
YAML parsers can differ in edge-case interpretation depending on supported YAML versions and implementation choices.
Users should validate important configuration against the schema or application that will consume it.
Very large YAML documents may be limited by browser or server memory.
Official References
The following official resources were used when developing this tool and are useful for further reading.