YAML to JSON Converter

YAML and JSON: the same data, different clothes

JSON and YAML describe the same three things — mappings, sequences and scalars — so any YAML document that holds plain data has an exact JSON equivalent. JSON is in fact a strict subset of YAML. This converter parses the YAML into an in-memory value and re-serialises it as JSON, which is why round-tripping data through it is lossless for anything JSON can represent.

What does not carry over is everything JSON lacks a slot for. Comments are the big one: YAML "#" comments are stripped because JSON has no comment syntax. Anchors and aliases (&x / *x) are resolved — the JSON gets a full copy wherever the alias appeared, not a reference. Custom tags (!!python/object and the like) are not supported and will error.

Scalar interpretation follows the core schema. true and false are booleans; the YAML 1.1 habit of treating yes, no, on and off as booleans is not applied, so those stay strings. A bare number is a number; a date-like value such as 2024-01-01 is kept exactly as written, as a string (JSON has no date type); and everything else is a string. Quote a value in the YAML if you need to force it to stay text.

Two common errors: YAML forbids tab characters for indentation — use spaces — and this tool converts a single document, not a multi-document stream separated by "---". The parser reports the line and column of a syntax error so you can find it quickly.

Parsing and serialising run entirely in your browser via the js-yaml library. Nothing you paste is uploaded, and the tool works offline once loaded.

Worked example

YAML in:
port: 8080
hex: 0x1F
enabled: yes
release: 2024-01-01
big: 12345678901234567890
base: &base {timeout: 30}
prod: *base

JSON out:
{"port":8080,"hex":31,"enabled":"yes","release":"2024-01-01",
 "big":12345678901234567000,"base":{"timeout":30},"prod":{"timeout":30}}

Note what changed: the hexadecimal number became decimal, yes stayed a string (YAML 1.2), the date stayed text, the anchor was expanded into a full copy, and the very large integer lost precision — JavaScript numbers are exact only up to 9,007,199,254,740,991. Quote big IDs in the YAML so they come through as strings.

Fixing common parse errors

• Tabs: indentation must use spaces only.
• Colons in values: “title: Part 2: The Return” is ambiguous — quote the value.
• A value starting with @, `, *, & or ! needs quotes, because those characters have special meaning at the start of a scalar.
• Multiple documents separated by --- must be converted one at a time.

Why convert YAML to JSON

• Validation: JSON Schema tools and many editors validate JSON more readily; convert a config file to check it against a schema.
• Querying: jq and most programming languages read JSON natively, which makes it easy to pull a single value out of a large Kubernetes manifest or CI file.
• APIs: most REST APIs accept JSON, not YAML, so request bodies written as YAML for readability need converting before they are sent.
• Debugging: seeing the resolved data — anchors expanded, types made explicit — shows what the program reading the YAML will actually receive, which is often where indentation mistakes reveal themselves.