Hexadecimal number in JSON
JSON numbers are decimal only. `0x1F` comes from a language literal or from a value that should have stayed a string, such as a colour code or a memory address.
The input
{"a": 0x1F}{"a": 31}How to fix it
Convert to decimal, or quote it as a string if the hex form is the meaningful representation.
Colour values like `0xFF0000` almost always want to be the string `"#FF0000"`.
What each parser reports
Every message below was captured by running this exact input through the parser named. 16 of 21 parsers rejected it; 5 accepted it.
| Parser | Exact message |
|---|---|
| CPython json.loads CPython 3.12.3 | Expecting ',' delimiter: line 1 column 8 (char 7)what this message means → |
| encoding/json Unmarshal Go go1.22.2 | invalid character 'x' after object key:value pairwhat this message means → |
| Gson Java 21.0.12 | accepted — no error |
| Gson JsonParser (lenient off) Java 21.0.12 | accepted — no error |
| hjson Node.js 22.22.2 | End of input while parsing an object (missing '}') at line 1,11 >>>"a": 0x1F} ...what this message means → |
| Jackson ObjectMapper Java 21.0.12 | Unexpected character ('x' (code 120)): was expecting comma to separate Object entrieswhat this message means → |
| JavaScriptCore JSON.parse JavaScriptCore (Bun 1.4.1) | JSON Parse error: Expected '}'what this message means → |
| json-bigint Node.js 22.22.2 | Expected ',' instead of 'x'what this message means → |
| JSON5 Node.js 22.22.2 | accepted — no error |
| JSON::PP Perl 5.038002 | , or } expected while parsing object/hash, at character offset 7 (before "x1F}")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 | unexpected character, expected ',' or '}': line 1 column 8 (char 7)what this message means → |
| Ruby JSON.parse Ruby 3.2.3 | unexpected token at '{"a": 0x1F}' |
| serde_json::from_str Rust (serde_json 1.x) | expected `,` or `}` at line 1 column 8what this message means → |
| SpiderMonkey JSON.parse SpiderMonkey 115 | JSON.parse: expected ',' or '}' after property value in object at line 1 column 8 of the JSON datawhat this message means → |
| System.Text.Json Deserialize .NET 8.0.30 | 'x' is an invalid end of a number. Expected a delimiter. Path: $ | LineNumber: 0 | BytePositionInLine: 7.what this message means → |
| System.Text.Json JsonDocument .NET 8.0.30 | 'x' is an invalid end of a number. Expected a delimiter. LineNumber: 0 | BytePositionInLine: 7.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 ',' or '}' after property value in JSON at position 7 (line 1 column 8)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 | A number is base 10, optionally signed with a minus, with an optional fraction and exponent. The section states that leading zeros are not allowed, and that values which cannot be represented in its grammar — Infinity and NaN among them — are not permitted. |
| Ecma International | A number is decimal digits with no superfluous leading zero. Values such as Infinity and NaN are not permitted. |
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Leading zero in a JSON number
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Leading plus sign in a JSON number
JSON allows a leading minus but not a leading plus. Explicitly signed values from spreadsheets or telemetry formats trip this.…
Trailing decimal point in a JSON number
`1.` is valid in C and JavaScript but not in JSON, which requires at least one digit after the decimal point.…
Leading decimal point in a JSON number
`.5` is valid in several languages but JSON requires a digit before the decimal point.…
Bare minus sign where a number was expected
A minus with no digits after it. Typically a templated value that resolved to empty, leaving the sign behind.…