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jsonbeautifiers
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Python Verified by running the parser on CPython 3.14.3.

Invalid control character at: line L column C (char N)

A string contains a literal character below U+0020, usually a real newline or tab. JSON requires those to be escaped. Python has a strict=False option that accepts them, but the resulting document is still invalid for every other consumer.

Paste your JSON and see exactly where it breaks

Input

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What actually causes it

Ranked by how often each one turns out to be the answer.

  1. 01 Multi-line text inside a string

    Log excerpts, SQL, stack traces and templated HTML all carry real newlines.

    Breaks

    json.loads('{"sql": "SELECT *
FROM t"}')

    Works

    json.loads('{"sql": "SELECT *\\nFROM t"}')

  2. 02 JSON assembled with f-strings or concatenation

    Interpolated values are not escaped. Build a dict and use json.dumps, which escapes everything correctly.

    Breaks

    body = f'{{"note": "{note}"}}'

    Works

    body = json.dumps({"note": note})

  3. 03 A tab copied from a spreadsheet

    Invisible, and it survives copy and paste intact.

The same mistake in other runtimes

The underlying problem is identical; only the wording differs. If a colleague reports one of these, they are looking at the same thing you are.

JavaScript (V8) Bad control character in string literal in JSON at position 11 (line 1 column 12)

Questions

What does strict=False do?
json.loads(s, strict=False) allows control characters inside strings. It gets you moving, but the document remains invalid JSON, so anything downstream that is not Python will still reject it. Fix the producer instead.

Fix it now

Paste the payload into the tool above, or go straight to the one built for this job.

Escape the string properly