Use JsonReader.setLenient(true) to accept malformed JSON at line L column C path $…
This message comes from Gson on Java 21.0.12. In this registry it is produced by 4 distinct mistakes. Positions in the real message vary with your input; the causes do not.
What produces this message
Extra data after a JSON document
{"a": 1}{"b": 2}Exact message: Use JsonReader.setLenient(true) to accept malformed JSON at line 1 column 10 path $
Fix: Split the documents, or if you meant a stream of records, use NDJSON and parse one line at a time.
HTML received where JSON was expected
<!DOCTYPE html>
<html><body>500</body></html>Exact message: Use JsonReader.setLenient(true) to accept malformed JSON at line 1 column 12 path $
Fix: Check the HTTP status and the Content-Type header before parsing. Log the first 200 characters of the body when parsing fails so the actual page is visible in your logs.
NDJSON fed to a whole-document JSON parser
{"a":1}
{"a":2}Exact message: Use JsonReader.setLenient(true) to accept malformed JSON at line 2 column 2 path $
Fix: Read line by line and parse each line separately.
Trailing characters after a JSON document
{"a": 1} garbageExact message: Use JsonReader.setLenient(true) to accept malformed JSON at line 1 column 11 path $
Fix: Trim everything after the final closing brace, and check whatever produced the file for stray writes to stdout.
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 | Expecting value: line L column C (char N)Extra data: line L column C (char N) |
| Gson JsonParser (lenient off) | Use JsonReader.setLenient(true) to accept malformed JSON at line L column C path $… |
| JSON5 | JSON5: invalid character '<' at 1:1JSON5: invalid character 'g' at 1:10JSON5: invalid character '{' at 1:9JSON5: invalid character '{' at 2:1 |
| JSON::PP | garbage after JSON object, at character offset N (before "…")malformed JSON string, neither array, object, number, string or atom, at character offset N (before "…") |
| Jackson ObjectMapper | Unexpected character ('<' (code 60)): expected a valid value (JSON String, Number, Array, Object or token 'null', 'true' or 'false') |
| JavaScriptCore JSON.parse | JSON Parse error: Unable to parse JSON stringJSON Parse error: Unrecognized token '<' |
| Newtonsoft.Json JsonConvert | Additional text encountered after finished reading JSON content: g. Path '', line L, position N.Additional text encountered after finished reading JSON content: {. Path '', line L, position N.Unexpected character encountered while parsing value: <. Path '', line L, position N. |
| Newtonsoft.Json JsonTextReader | Additional text encountered after finished reading JSON content: g. Path '', line L, position N.Additional text encountered after finished reading JSON content: {. Path '', line L, position N.Unexpected character encountered while parsing value: <. Path '', line L, position N. |
| Ruby JSON.parse | unexpected token at '…' |
| SpiderMonkey JSON.parse | JSON.parse: unexpected character at line L column C of the JSON dataJSON.parse: unexpected non-whitespace character after JSON data at line L column C of the JSON data |
| System.Text.Json Deserialize | '<' is an invalid start of a value. Path: $ | LineNumber: L | BytePositionInLine: C.'g' is invalid after a single JSON value. Expected end of data. Path: $ | LineNumber: L | BytePositionInLine: C.'{' is invalid after a single JSON value. Expected end of data. Path: $ | LineNumber: L | BytePositionInLine: C. |
| System.Text.Json JsonDocument | '<' is an invalid start of a value. LineNumber: L | BytePositionInLine: C.'g' is invalid after a single JSON value. Expected end of data. LineNumber: L | BytePositionInLine: C.'{' is invalid after a single JSON value. Expected end of data. LineNumber: L | BytePositionInLine: C. |
| V8 JSON.parse | Unexpected non-whitespace character after JSON at position N (line L column C)Unexpected token '<', "…"... is not valid JSON |
| encoding/json Unmarshal | invalid character '<' looking for beginning of valueinvalid character 'g' after top-level valueinvalid character '{' after top-level value |
| hjson | Found EOF while looking for a key name (check your syntax) at line L,30Syntax error, found trailing characters at line L,1 >>>{"a":2} {"a":3} ...Syntax error, found trailing characters at line L,8Syntax error, found trailing characters at line L,9 |
| json-bigint | Syntax errorUnexpected '<' |
| json_decode | Syntax error |
| orjson | unexpected character, expected a JSON value: line L column C (char N)unexpected content after document: line L column C (char N) |
| serde_json::from_str | expected value at line L column Ctrailing characters at line L column C |
| ujson | Expected object or valueTrailing data |
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.