Unexpected character ('x' (code 120)): was expecting comma to separate Object entries
This message comes from Jackson ObjectMapper on Java 21.0.12. In this registry it is produced by 1 distinct mistake. Positions in the real message vary with your input; the causes do not.
Causes
What produces this message
Hexadecimal number in JSON
Input
{"a": 0x1F}Exact message: Unexpected character ('x' (code 120)): was expecting comma to separate Object entries
Fix: Convert to decimal, or quote it as a string if the hex form is the meaningful representation.
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 | Expecting ',' delimiter: line L column C (char N) |
| JSON::PP | , or } expected while parsing object/hash, at character offset N (before "…") |
| JavaScriptCore JSON.parse | JSON Parse error: Expected '}' |
| Ruby JSON.parse | unexpected token at '…' |
| SpiderMonkey JSON.parse | JSON.parse: expected ',' or '}' after property value in object at line L column C of the JSON data |
| System.Text.Json Deserialize | 'x' is an invalid end of a number. Expected a delimiter. Path: $ | LineNumber: L | BytePositionInLine: C. |
| System.Text.Json JsonDocument | 'x' is an invalid end of a number. Expected a delimiter. LineNumber: L | BytePositionInLine: C. |
| V8 JSON.parse | Expected ',' or '}' after property value in JSON at position N (line L column C) |
| encoding/json Unmarshal | invalid character 'x' after object key:value pair |
| hjson | End of input while parsing an object (missing '}') at line L,11 |
| json-bigint | Expected ',' instead of 'x' |
| json_decode | Syntax error |
| orjson | unexpected character, expected ',' or '}': line L column C (char N) |
| serde_json::from_str | expected `,` or `}` at line L column C |
| ujson | Unexpected character in found when decoding object value |
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.