Trailing comma in a JSON object
A comma after the last member of an object. JavaScript, Python and most modern languages allow this in their own literal syntax, so it is very easy to leave behind when hand-editing or when a template loop writes the last item.
The input
{"a": 1,}{"a": 1}How to fix it
Delete the comma before the closing brace.
This is the single most common cause of a JSON parse failure in hand-edited config files. If you need trailing commas to survive, you are looking for JSON5 or JSONC, not JSON.
What each parser reports
Every message below was captured by running this exact input through the parser named. 17 of 21 parsers rejected it; 4 accepted it.
| Parser | Exact message |
|---|---|
| CPython json.loads CPython 3.12.3 | Expecting property name enclosed in double quotes: line 1 column 9 (char 8)what this message means → |
| encoding/json Unmarshal Go go1.22.2 | invalid character '}' looking for beginning of object key stringwhat this message means → |
| Gson Java 21.0.12 | Expected name at line 1 column 10 path $.awhat this message means → |
| Gson JsonParser (lenient off) Java 21.0.12 | Expected name at line 1 column 10 path $.awhat this message means → |
| hjson Node.js 22.22.2 | accepted — no error |
| Jackson ObjectMapper Java 21.0.12 | Unexpected character ('}' (code 125)): was expecting double-quote to start field namewhat this message means → |
| JavaScriptCore JSON.parse JavaScriptCore (Bun 1.4.1) | JSON Parse error: Property name must be a string literalwhat this message means → |
| json-bigint Node.js 22.22.2 | Bad string |
| JSON5 Node.js 22.22.2 | accepted — no error |
| JSON::PP Perl 5.038002 | unexpected end of string while parsing JSON string, at character offset 9 (before "(end of string)")what this message means → |
| json_decode PHP 8.3.6 | Syntax error |
| Newtonsoft.Json JsonConvert Newtonsoft.Json 13.0.3 on .NET 8.0.30 | accepted — no error |
| Newtonsoft.Json JsonTextReader Newtonsoft.Json 13.0.3 on .NET 8.0.30 | accepted — no error |
| orjson CPython 3.12.3 | trailing comma is not allowed: line 1 column 8 (char 7)what this message means → |
| Ruby JSON.parse Ruby 3.2.3 | unexpected token at '{"a": 1,}' |
| serde_json::from_str Rust (serde_json 1.x) | trailing comma at line 1 column 9what this message means → |
| SpiderMonkey JSON.parse SpiderMonkey 115 | JSON.parse: expected double-quoted property name at line 1 column 9 of the JSON datawhat this message means → |
| System.Text.Json Deserialize .NET 8.0.30 | The JSON object contains a trailing comma at the end which is not supported in this mode. Change the reader options. Path: $ | LineNumber: 0 | BytePositionInLine: 8.what this message means → |
| System.Text.Json JsonDocument .NET 8.0.30 | The JSON object contains a trailing comma at the end which is not supported in this mode. Change the reader options. LineNumber: 0 | BytePositionInLine: 8.what this message means → |
| ujson CPython 3.12.3 | Unexpected character in found when decoding object valuewhat this message means → |
| V8 JSON.parse Node.js 22.22.2 | Expected double-quoted property name in JSON at position 8 (line 1 column 9)what this message means → |
What the specification says
The exact sections that govern this error. Descriptions are our paraphrase; follow the links for the normative text.
| Body | Section |
|---|---|
| IETF | An object is curly brackets around zero or more members. A name is a string, a single colon separates name from value, and a single comma separates a value from a following name. |
| Ecma International | Gives the object grammar and states that the syntax does not require name strings to be unique and assigns no significance to member ordering. |
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