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YAML to JSON and JSON to YAML

Est. read: 6 minDeveloper
Arrows between YAML and JSON icons representing conversion

Summary

Definition: YAML and JSON model similar data but follow different constraints.

Why it matters: Conversions can lose meaning if unsupported features or types are used.

Pitfall: Plain scalars may resolve to unexpected types.

Key terms
YAML
Human-friendly data format with multiple schemas.
JSON
Strict data format with a small fixed type set.
Plain scalar
Unquoted YAML value resolved by schema rules.
JSON Schema
YAML schema limited to JSON-compatible types.
Type coercion
Automatic conversion of plain scalars.

How YAML and JSON map

YAML 1.2 was designed to be compatible with JSON, but only a subset of YAML maps cleanly to JSON.

YAML vs JSON
YAML
Multiple schemas and rich syntax.
JSON
Single schema and strict syntax.
Both
Objects, arrays, scalars.

Only YAML data that conforms to the YAML JSON Schema can be converted to JSON safely.

What does not survive conversion

Some YAML features have no JSON equivalent and are discarded or flattened during conversion.

  • Comments
  • Anchors and aliases
  • Custom tags
  • Multiple documents
  • Merge keys

Common mix-up: YAML 1.2 is a superset of JSON syntax, not a guarantee of round-trip safety.

Type conversion pitfalls

YAML resolves unquoted values using schema rules. Different parsers may apply YAML 1.1 or 1.2 behavior.

Implicit typing can change IDs, flags, or ports if values are not quoted.

Example

Plain scalars may change type during conversion.

YAML to JSON
user:
  id: "01"
  active: yes
  roles:
    - admin
    - editor

Validate the output

Always validate the converted data to confirm structure and types.

Practical check
  • Convert YAML to JSON.
  • Lint the JSON for validity.
  • Convert back to YAML if needed.
  • Review types for critical fields.

Tools and workflows

Most conversion bugs come from assuming all YAML is JSON-compatible. Treat YAML as a superset with limits.