trailing comma at line L column C
This message comes from serde_json::from_str on Rust (serde_json 1.x). In this registry it is produced by 2 distinct mistakes. Positions in the real message vary with your input; the causes do not.
Causes
What produces this message
Trailing comma in a JSON array
Input
[1, 2, 3,]Exact message: trailing comma at line 1 column 10
Fix: Delete the comma before the closing bracket, or build the array with a join instead of manual concatenation.
Trailing comma in a JSON object
Input
{"a": 1,}Exact message: trailing comma at line 1 column 9
Fix: Delete the comma before the closing brace.
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 property name enclosed in double quotes: line L column C (char N)Expecting value: line L column C (char N) |
| Gson | Expected name at line L column C path $… |
| Gson JsonParser (lenient off) | Expected name at line L column C path $… |
| JSON::PP | malformed JSON string, neither array, object, number, string or atom, at character offset N (before "…")unexpected end of string while parsing JSON string, at character offset N (before "…") |
| Jackson ObjectMapper | Unexpected character (']' (code 93)): expected a valid value (JSON String, Number, Array, Object or token 'null', 'true' or 'false')Unexpected character ('}' (code 125)): was expecting double-quote to start field name |
| JavaScriptCore JSON.parse | JSON Parse error: Property name must be a string literalJSON Parse error: Unexpected comma at the end of array expression |
| Ruby JSON.parse | unexpected token at '…' |
| SpiderMonkey JSON.parse | JSON.parse: expected double-quoted property name at line L column C of the JSON dataJSON.parse: unexpected character at line L column C of the JSON data |
| System.Text.Json Deserialize | The JSON array contains a trailing comma at the end which is not supported in this mode. Change the reader options. Path: $ | LineNumber: L | BytePositionInLine: C.The JSON object contains a trailing comma at the end which is not supported in this mode. Change the reader options. Path: $ | LineNumber: L | BytePositionInLine: C. |
| System.Text.Json JsonDocument | The JSON array contains a trailing comma at the end which is not supported in this mode. Change the reader options. LineNumber: L | BytePositionInLine: C.The JSON object contains a trailing comma at the end which is not supported in this mode. Change the reader options. LineNumber: L | BytePositionInLine: C. |
| V8 JSON.parse | Expected double-quoted property name in JSON at position N (line L column C)Unexpected token ']', "[1, 2, 3,]" is not valid JSON |
| encoding/json Unmarshal | invalid character ']' looking for beginning of valueinvalid character '}' looking for beginning of object key string |
| json-bigint | Bad stringUnexpected ']' |
| json_decode | Syntax error |
| orjson | trailing comma is not allowed: line L column C (char N) |
| ujson | Unexpected character found when decoding array value (1)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.