python -m json.tool: pretty-print and validate JSON

python -m json.tool file.json pretty-prints a JSON file, and exits with status 1 and an error message when the input is not valid JSON. It reads standard input when no file is given, so it also works in pipes. Since Python 3.14 the same CLI is available as python -m json; json.tool keeps working.

Pretty-print from a pipe

echo '{"name": "errcodex", "tags": ["json", "cli"], "verified": true}' | python -m json.tool

{
    "name": "errcodex",
    "tags": [
        "json",
        "cli"
    ],
    "verified": true
}

Validate a file

Invalid JSON prints the parser error with line and column, and the exit status is 1, which makes it usable in scripts and CI.

printf '{"a": 1,}\n' > bad.json
python -m json.tool bad.json

Illegal trailing comma before end of object: line 1 column 8 (char 7)

Sort keys, change indentation, compact output

echo '{"b": 2, "a": {"y": 1, "x": 2}}' > data.json
python -m json.tool --sort-keys --indent 2 data.json
python -m json.tool --compact data.json

{
  "a": {
    "x": 2,
    "y": 1
  },
  "b": 2
}
{"b":2,"a":{"y":1,"x":2}}

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