Explainer1 min readUpdated July 1, 2026

What is YAML?

Short answer

YAML (YAML Ain't Markup Language) is a data serialization format designed to be easy for humans to read and write. It uses indentation instead of brackets and is common for configuration files like CI pipelines and Kubernetes manifests.

What YAML is for

YAML stores structured data — the same objects, arrays, strings, and numbers as JSON — but with a syntax tuned for humans. It is the default for many config files: GitHub Actions, Docker Compose, Kubernetes, and more.

How the syntax works

name: utilumo
version: 1
features:
  - search
  - dark mode
enabled: true

A small YAML document

Indentation (spaces, never tabs) shows nesting
key: value pairs map names to values
A leading - marks each item in a list
Strings usually need no quotes; numbers and booleans are bare
# starts a comment — something JSON does not allow

Try it: YAML to JSONConvert YAML to JSON locally to inspect or validate its structure.Open tool

Indentation is significantBecause YAML uses indentation for structure, a stray space or a tab can change the meaning or break the file. Use consistent spaces and validate when in doubt.

YAML vs JSON

YAML is easier to read and supports comments, so it wins for hand-edited config. JSON is stricter and universal for APIs and data exchange. In fact, all JSON is valid YAML. See YAML vs JSON.

References

Questions

What does YAML stand for?

It is a recursive acronym: 'YAML Ain't Markup Language.' The name signals that it is for data, not for marking up documents like HTML.

Can I use tabs in YAML?

No. YAML forbids tabs for indentation because their width is ambiguous. Use spaces, and be consistent about how many per level.

Does this send my data anywhere?

No. Utilumo's developer tools parse and transform input inside the browser tab. Nothing is uploaded, stored, or logged.