YAML to JSON Converter

What is lost going from YAML to JSON

The data survives. YAML's authoring conveniences do not, because JSON has no way to express them. That makes this direction genuinely lossy, and it is worth knowing which parts of your file will not come back.

This page detects each of these in your input and lists them, with a count, rather than converting silently. The intent is that you know what changed before you rely on the output.

How to convert

1. Paste your YAML A parse failure names the line and column, and translates the common cases — tabs, misaligned indentation, an undefined alias — into plain English.
2. Choose the JSON formatting Two or four spaces for readability, or minified for transport.
3. Read the lossy-feature panel It lists what could not survive, with counts, so nothing disappears without notice.
4. Check the type-change warnings Timestamps, infinities and non-string keys are called out individually because they change type rather than just formatting.

Anchors and merge keys, resolved

Anchors are YAML's way of writing something once and reusing it. They are extremely common in CI configuration and Docker Compose files.

defaults: &defaults
  retries: 3
  timeout: 30

primary:
  <<: *defaults
  host: primary.internal

replica:
  <<: *defaults
  host: replica.internal

Converted to JSON, the shared block is copied into each place that referenced it:

{
  "defaults": { "retries": 3, "timeout": 30 },
  "primary":  { "retries": 3, "timeout": 30, "host": "primary.internal" },
  "replica":  { "retries": 3, "timeout": 30, "host": "replica.internal" }
}

The values are correct. What is gone is the relationship — that all three were meant to stay in step. Change retries in the JSON and you have to change it in three places instead of one.

Two details worth knowing about anchors. First, an anchor must be defined before the alias that uses it; a forward reference is a parse error, and this page reports it as one. Second, an alias expands to a full copy in most parsers, so a deeply nested anchor referenced many times can expand a small file into a very large JSON document.

Examples: values whose type changes

YAML infers types from unquoted text, so a value that looked like a string in the file may not arrive as one.

The date row surprises people most. Writing released: 2026-03-14 produces a full timestamp at midnight UTC, not the date string you typed. If you want the literal text, quote it in the YAML: released: '2026-03-14'.

Common parse errors and what they mean

• A tab character. YAML forbids tabs as indentation, full stop. This is the most common cause of a file that looks fine in one editor and fails in CI. The error names the line.
• Inconsistent indentation. Siblings must align exactly. Being one space out is a structural error, not a style problem, and can silently nest a key under the wrong parent when it happens to still be valid.
• A duplicate key. Legal YAML, but the later value wins silently. It is almost always a mistake — usually two people editing the same config — so it is reported here.
• An undefined alias. *name without a preceding &name. Usually caused by copying a block out of a larger file and leaving the anchor behind.
• An unterminated quoted string. A missing closing quote lets the parser run to the end of the document, so the reported line is often far from the real problem. Look upward from it.
• A colon inside an unquoted value. title: Report: Q1 is ambiguous. Quote the value.
• Missing space after the colon. key:value is a single scalar string, not a mapping. YAML needs key: value.

Use cases

• Feeding a config to code that expects JSON. Many libraries and CLI tools take JSON only, while the config is maintained as YAML.
• Querying a config. Convert to JSON and then use the JSONPath Tester to pull out a deeply nested value.
• Validating against a schema. JSON Schema tooling works on JSON, so converting first lets you check a YAML config with the JSON Schema Validator.
• Understanding what your YAML actually parsed to. This is the strongest use: the JSON shows the real types, revealing that version: 1.0 became a number or that a date became a timestamp.
• Diffing two configs meaningfully. Convert both with keys sorted and compare the JSON, so reordering and comment changes do not show up as differences.
• Debugging an anchor. The expanded JSON shows exactly what a merge key resolved to, which is hard to read from the YAML alone.

To go back the other way, JSON to YAML handles the quoting correctly. The YAML Formatter tidies a file without converting it.

Privacy

Parsing runs in your browser with js-yaml. The YAML is not uploaded, which matters because config files routinely contain internal hostnames, service names and secret references. Usage analytics record only the indentation setting, a coarse size band and how many lossy features were detected.