YAML to JSON Converter (and JSON to YAML)

YAML and JSON describe the same data

JSON and YAML both describe maps (objects), lists (arrays), and scalars (strings, numbers, booleans, null). YAML 1.2 is designed so that almost any JSON document is also valid YAML. The difference is syntax: JSON uses braces, brackets, and quotes; YAML uses indentation and dashes. That is why Kubernetes, Docker Compose, GitHub Actions, and Ansible pick YAML for files people write by hand, and APIs pick JSON for data machines exchange.

This converter goes both ways. Edit the YAML side and the JSON updates; edit the JSON side and the YAML updates. It uses the js-yaml library, loaded only on this page, and runs entirely in your browser. Secrets in a values.yaml or a CI config never leave your machine.

Worked example: a Kubernetes manifest

The preloaded example is a Deployment. In YAML, spec: is followed by indented keys, and containers: is a list where each item starts with a dash. In JSON, the same structure becomes "spec": { "replicas": 3, ... } and "containers": [ { "name": "web", ... } ]. kubectl accepts both formats, so converting is safe. The JSON form is handy for jq queries, for kubectl patch, or for pasting into code.

Comments do not survive. JSON has no comment syntax, so # lines in your YAML are dropped when you convert to JSON. If you round-trip back to YAML, they are gone for good. Keep the original file under version control.

Reading YAML error messages

When the YAML is invalid, the tool shows the line and column where the parser gave up, plus the reason. The most common ones:

Bad indentation: a key is indented by a different number of spaces than its siblings. YAML does not care whether you use 2 or 4 spaces, but every sibling must use the same amount.

Tabs: YAML forbids tab characters for indentation. An editor that inserts tabs will break your file in a way that is invisible on screen. Replace them with spaces.

Missing space after a colon: key:value is read as a single string, not a key and a value. It needs to be key: value.

Unquoted special characters: a value that starts with @, `, *, &, !, |, >, %, or { or [ must be quoted. So must a string containing ": " or " #".

Duplicate keys: the same key twice in one map is an error in js-yaml, which protects you from silently losing the first value.

The type traps

YAML guesses types from unquoted values, and the guesses depend on the YAML version. This tool follows YAML 1.2 (the core schema): true, false, and null are special, numbers are numbers, and everything else is a string.

The famous Norway problem comes from YAML 1.1, where NO, no, off, and yes were booleans, so a country code list with NO turned into false. YAML 1.2 fixed that, but older parsers (including PyYAML and many Ruby and Go tools) still use 1.1 rules. If a value must be a string, quote it: "NO", "on", "1.10".

Version numbers and zip codes. version: 1.10 is the number 1.1. zip: 02134 is the number 2134 in YAML 1.2. Quote them. The same problem hits JSON in reverse: once converted, an unquoted 1.10 is a number and the trailing zero is gone.

Large integers. Numbers beyond 2^53 lose precision in JavaScript, so a 19-digit ID can change by the time it reaches JSON. Quote big IDs in the YAML.

Multiple documents and anchors

A YAML file can hold several documents separated by ---, common in Kubernetes files that bundle a Deployment and a Service. The converter turns multiple documents into a JSON array, one element per document, and tells you how many it found.

Anchors (&name) and aliases (*name) are expanded during conversion, so the JSON shows the full, repeated data. Merge keys (<<: *defaults) are a YAML 1.1 extension that YAML 1.2 dropped, so here they show up as a literal "<<" key. Tools like Docker Compose and GitLab CI still honor them; if you need the merged result in JSON, merge by hand. Going the other way, from JSON to YAML, the tool writes plain output without anchors, so it is easy to read and diff.