JSON · YAML formatter and converter

What it does

• JSON: indent with 2 or 4 spaces or a tab, or minify to one line (the same layout as Python json.dumps). Numbers are kept as written, so big integers such as 12345678901234567890 and digits like 1.50 are not lost. Syntax errors are reported at the same line and column as Python json.
• YAML → JSON: the syntax is read by the proven yaml library (ISC); unquoted values are resolved with the rules of the selected version — the core schema of the 1.2 spec, or the same rules as PyYAML for 1.1 (including the << merge key). Values the two versions read differently are listed in a table.
• JSON → YAML: values such as "no", "0777" and "2001-12-14" are quoted so that they stay text in either version. The result is read back before it is shown to make sure the values are the same.

YAML traps

The country code NO (Norway) turning into false is the first row of this table. If a config file is read by a 1.1 parser such as PyYAML, select 1.1 to check it.

How the check was made

Before release 244 cases were compared, all matching: 25 JSON documents × (2 spaces, 4 spaces, one line, sorted keys) = Python json.dumps(ensure_ascii=False) for 100 cases (two documents whose number spellings are kept and one with an unpaired surrogate were compared by value), the line and column of 32 broken JSON inputs = Python json, 35 YAML documents converted as 1.1 = PyYAML 6.0.3 safe_load (inputs that give an error also fail in PyYAML or hold values JSON cannot express), the 1.2 reading of the same YAML = the yaml library's core schema in 34 cases, 25 JSON → YAML results read back by PyYAML and ruamel.yaml 0.19.1 = the original values, and the 18 trap values above.

Common mistakes

• A trailing comma [1, 2,], single quotes {'a': 1} or comments — all errors in JSON.
• Tabs in YAML indentation — YAML does not allow tabs for indentation.
• Reading big IDs with JSON.parse — integers beyond 2⁵³ are rounded. Send them as strings.
• Writing the same key twice — JSON parsers usually take the last value, but YAML forbids it and some parsers stop with an error.