JSON Parse error: Unterminated string
This message comes from JavaScriptCore JSON.parse on JavaScriptCore (Bun 1.4.1). In this registry it is produced by 4 distinct mistakes. Positions in the real message vary with your input; the causes do not.
Causes
What produces this message
Raw NUL byte inside a JSON string
Input
{"a": "x y"}Exact message: JSON Parse error: Unterminated string
Fix: Escape it as `\u0000`, or — better — base64-encode binary data instead of putting raw bytes in a string.
Literal newline inside a JSON string
Input
{"a": "line1
line2"}Exact message: JSON Parse error: Unterminated string
Fix: Escape it as `\n`. Any correct serialiser does this for you.
Literal tab inside a JSON string
Input
{"a": "col1 col2"}Exact message: JSON Parse error: Unterminated string
Fix: Escape it as `\t`.
Unterminated string in JSON
Input
{"a": "hello}Exact message: JSON Parse error: Unterminated string
Fix: Escape internal double quotes as `\"`, and check that every string has a matching closing quote.
Same bug, other languages
What other parsers say about the same input
If a colleague reports a different message for what looks like the same file, this is why.
| Parser | Message for the same inputs |
|---|---|
| CPython json.loads | Invalid control character at: line L column C (char N)Unterminated string starting at: line L column C (char N) |
| Gson | Unterminated string at line L column C path $… |
| Gson JsonParser (lenient off) | Unterminated string at line L column C path $… |
| JSON5 | JSON5: invalid character '\n' at 2:0JSON5: invalid end of input at 1:14 |
| JSON::PP | invalid character 0x0 encountered while parsing JSON string, at character offset N (before "…")invalid character 0x9 encountered while parsing JSON string, at character offset N (before "…")invalid character 0xA encountered while parsing JSON string, at character offset N (before "…")unexpected end of string while parsing JSON string, at character offset N (before "…") |
| Jackson ObjectMapper | Illegal unquoted character ((CTRL-CHAR, code 0)): has to be escaped using backslash to be included in string valueIllegal unquoted character ((CTRL-CHAR, code 10)): has to be escaped using backslash to be included in string valueIllegal unquoted character ((CTRL-CHAR, code 9)): has to be escaped using backslash to be included in string valueUnexpected end-of-input: was expecting closing quote for a string value |
| Newtonsoft.Json JsonConvert | Unterminated string. Expected delimiter: ". Path 'a', line L, position N. |
| Newtonsoft.Json JsonTextReader | Unterminated string. Expected delimiter: ". Path 'a', line L, position N. |
| Ruby JSON.parse | unexpected token at '…' |
| SpiderMonkey JSON.parse | JSON.parse: bad control character in string literal at line L column C of the JSON dataJSON.parse: unterminated string at line L column C of the JSON data |
| System.Text.Json Deserialize | '0x00' is invalid within a JSON string. The string should be correctly escaped. Path: $ | LineNumber: L | BytePositionInLine: C.'0x09' is invalid within a JSON string. The string should be correctly escaped. Path: $ | LineNumber: L | BytePositionInLine: C.'0x0A' is invalid within a JSON string. The string should be correctly escaped. Path: $ | LineNumber: L | BytePositionInLine: C.Expected end of string, but instead reached end of data. Path: $ | LineNumber: L | BytePositionInLine: C. |
| System.Text.Json JsonDocument | '0x00' is invalid within a JSON string. The string should be correctly escaped. LineNumber: L | BytePositionInLine: C.'0x09' is invalid within a JSON string. The string should be correctly escaped. LineNumber: L | BytePositionInLine: C.'0x0A' is invalid within a JSON string. The string should be correctly escaped. LineNumber: L | BytePositionInLine: C.Expected end of string, but instead reached end of data. LineNumber: L | BytePositionInLine: C. |
| V8 JSON.parse | Bad control character in string literal in JSON at position N (line L column C)Unterminated string in JSON at position N (line L column C) |
| encoding/json Unmarshal | invalid character '\n' in string literalinvalid character '\t' in string literalinvalid character '\x00' in string literalunexpected end of JSON input |
| hjson | Bad string at line L,13Bad string containing newline at line L,0 |
| json-bigint | Bad string |
| json_decode | Control character error, possibly incorrectly encoded |
| orjson | unexpected control character in string: line L column C (char N)unexpected end of data: line L column C (char N) |
| serde_json::from_str | EOF while parsing a string at line L column Ccontrol character (\u0000-\u001F) found while parsing a string at line L column C |
| ujson | Unmatched '"' when decoding 'string' |
Sources
Standards this registry is checked against
- RFC 8259 (STD 90) — The JavaScript Object Notation (JSON) Data Interchange Format, T. Bray, Ed., 2017. The IETF Internet Standard for JSON. Obsoletes RFC 7159 and RFC 4627.
- ECMA-404, 2nd edition — The JSON Data Interchange Syntax, Ecma International, 2017. Ecma’s grammar for JSON. A normative reference of RFC 8259; the two define the same syntax.
- The Unicode Standard — The Unicode Standard, Core Specification, The Unicode Consortium, current. Normatively referenced by RFC 8259 for the definition of a character.
- IEEE 754-2019 — IEEE Standard for Floating-Point Arithmetic, IEEE, 2019. Referenced by RFC 8259 §6 as the basis for its interoperability guidance on numbers.
Only standards bodies and peer-reviewed venues are cited. Error strings on this site are observed by executing each parser; the standards above define what the parser is reacting to.