YAML is a data-serialization format that stores structured software configuration in readable text files. It uses indentation, key-value pairs, and lists to describe settings that tools and applications can read. YAML is commonly used for deployment, automation, and application configuration, but whitespace mistakes can change its meaning.
YAML
What Is YAML?
YAML is a readable text format for structured software configuration. YAML means YAML Ain't Markup Language. A YAML file uses.yaml or.yml, which are equivalent extensions.
YAML Format and Basic Syntax
YAML uses spaces to show structure. Never use tabs.
- Create mappings with
name: value. - Create lists with a leading hyphen.
- Indent nested settings consistently.
- Add notes after
#; quote values that could be misread.
YAML vs. JSON
Both represent structured data, but they serve different editing needs.
| Feature | YAML | JSON |
|---|---|---|
| Readability | Indentation-based | Braces and brackets |
| Comments | Supported | Not supported |
| Compatibility | Valid JSON is valid YAML 1.2 | YAML is not always valid JSON |
Where YAML Files Are Used
YAML commonly defines software behavior outside application code.
- Application settings and feature configuration.
- Docker Compose files, including docker-compose.yml.
- CI/CD workflows and Kubernetes manifests.
- Automation playbooks.
Benefits of YAML
YAML is practical for configuration maintained in version control.
- Easy for people to review and edit.
- Comments document why a setting exists.
- Nesting expresses related settings clearly.
Practical Limits of YAML
Readable does not mean error-proof.
- One incorrect indent can alter the structure.
- Unquoted values may be interpreted unexpectedly.
- Tools differ in duplicate-key handling.
- Valid syntax can still fail a tool's schema.
How to Validate a YAML File
Validation should check both syntax and the target tool's rules.
- Format indentation consistently.
- Run a YAML lint or formatter.
- Validate against the tool's schema.
- Review the change and test safely.
YAML in Emergent
Emergent helps teams build and ship applications that use configuration files and integrations. Explore the Emergent glossary and its guide to app design and development to plan configuration-driven software.
Frequently Asked Questions
Your Questions, Answered
This will automatically populate, don't change
Don't change this element unless you know what you are doing
Are.yml and.yaml the same?
Yes. Both extensions identify YAML files, though.yaml is the preferred extension in the YAML specification.
Is YAML a script?
No. YAML describes data and configuration. A separate tool reads it and performs actions.
Is YAML just JSON?
No. YAML supports JSON-compatible data but adds indentation-based syntax, comments, and block text.
How do I validate a YAML file?
Use a YAML linter for syntax, then validate it with the schema or command provided by the tool that consumes it.
Is YAML still used?
Yes. It remains common in application configuration, containers, CI/CD pipelines, Kubernetes, and automation tools.
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