YAML to JSON converter and validator

YAML ("YAML Ain't Markup Language") is a human-friendly data format built on indentation. It is everywhere in DevOps and development:

• Docker Compose files (compose.yaml),
• Kubernetes manifests and Helm values,
• CI/CD pipelines: GitHub Actions workflows, GitLab CI, CircleCI,
• Ansible playbooks,
• OpenAPI (Swagger) specifications,
• front matter in Markdown files and static site generators.

JSON and YAML describe the same kinds of data: maps (objects), lists and scalar values. In fact, nearly every JSON document is also valid YAML. Converting between them is useful when one tool wants JSON and another wants YAML, or when you want to check exactly how a YAML file is interpreted.

Feature	Example
Key-value pairs	name: my-app
Nested maps by indentation	company: then city: Austin
Lists	- pdf on separate lines
Inline lists and maps	[a, b], {x: 1, y: 2}
Quoted strings	"line\nbreak", 'single'
Multiline blocks	| keeps line breaks, > folds them into spaces
Comments	# ignored
Types	numbers, true/false, null or ~

Not supported: anchors and aliases (&, *), custom tags (!), and multiple documents separated by --- in one file. Comments are lost on conversion because JSON has no comments.

Validate and format YAML parses the file and shows the line number and a description of the first problem, then outputs a cleanly re-indented version. Typical errors:

• Tabs used for indentation. YAML only allows spaces. Replace tabs with two spaces.
• Inconsistent indentation between sibling keys, which makes YAML think a key belongs to a different parent.
• A missing space after the colon: key:value is a plain string, not a pair.
• Duplicate keys in the same map, which the tool reports instead of silently keeping the last one.
• Unclosed quotes or brackets in inline values.

YAML guesses types for unquoted values, which sometimes surprises people:

• version: 1.10 becomes the number 1.1. Quote it: version: "1.10".
• zip: 02134 may lose its leading zero or be read as an octal number by some parsers. Quote ZIP codes and IDs.
• In older YAML 1.1 parsers, yes, no, on and off become booleans, so the country code NO for Norway turned into false. YAML 1.2 fixed this, but quoting such values is the safe habit.
• time: 12:30 can be read as a base-60 number by YAML 1.1 parsers.

Converting to JSON here is a quick way to see exactly what type each value ends up as.

Configuration files often contain hostnames, internal URLs and sometimes secrets. Everything here is parsed and converted in your browser, and nothing is uploaded. Still, it is good practice to keep real secrets out of YAML files and use environment variables or a secret manager instead.

Related tools: format and validate JSON with the JSON formatter, or turn JSON into a spreadsheet with JSON to CSV.