"Bad control character in string literal" Error, Explained

JSON string values can't contain a literal newline, tab, or other control character — they have to be escaped. This is a stricter rule than most people expect coming from other languages.

What triggers it

{
  "note": "line one
line two"
}

That raw newline inside the string breaks parsing with something like Bad control character in string literal in JSON at position 11. The same happens with a literal tab character, or with control characters copy-pasted in from another source (e.g. terminal output with embedded control codes).

Why JSON requires this

RFC 8259 requires control characters (U+0000 through U+001F) inside a string to be escaped — a newline must be written as \n, a tab as \t, and so on. This keeps JSON text unambiguous and safe to embed in other formats without a raw byte silently breaking line-based tooling (like log parsers) downstream.

How to fix it

• If you're generating JSON programmatically, use a real serializer (JSON.stringify, json.dumps) — it escapes control characters automatically. This error almost always means JSON was built by hand or via string concatenation.
• If you're hand-editing, replace the raw newline/tab inside the string with \n / \t.
• If the JSON came from somewhere else and you just need it fixed, paste it into JSON Repair.

Find the invisible byte

Start with the line and column reported by the parser, then inspect the raw bytes rather than the rendered text. A tab and several spaces can look identical, and a carriage return may be hidden by the editor. In JavaScript, inspect character codes below 32; in a terminal, a hex viewer can reveal 09 (tab), 0a (line feed), 0d (carriage return), or 00 (null).

Decide whether the character is meaningful data. If a newline belongs in the value, serialize it as \n; if it came from a damaged transport or delimiter, remove it before serialization. Do not replace every control character blindly: tabs and line breaks may be required after the JSON is decoded. Preserve one raw failing fixture and test the serializer so the producer cannot reintroduce the invalid byte.

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