Infinity is not valid JSON
Same root cause as NaN — a float overflowed and the serialiser wrote `Infinity` or `-Infinity`, which the JSON grammar has no token for.
The input
{"a": Infinity}{"a": null}How to fix it
Write `null`, a string, or clamp the value before serialising. Python: `json.dumps(x, allow_nan=False)`.
Division by zero in a metrics pipeline is the usual origin.
What each parser reports
Every message below was captured by running this exact input through the parser named. 14 of 21 parsers rejected it; 7 accepted it.
| Parser | Exact message |
|---|---|
| CPython json.loads CPython 3.12.3 | accepted — no error |
| encoding/json Unmarshal Go go1.22.2 | invalid character 'I' looking for beginning of valuewhat 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 1,15 >>>"a": Infinity} ...what this message means → |
| Jackson ObjectMapper Java 21.0.12 | Non-standard token 'Infinity': enable `JsonReadFeature.ALLOW_NON_NUMERIC_NUMBERS` to allowwhat this message means → |
| JavaScriptCore JSON.parse JavaScriptCore (Bun 1.4.1) | JSON Parse error: Unexpected identifier "Infinity"what this message means → |
| json-bigint Node.js 22.22.2 | Unexpected 'I' |
| JSON5 Node.js 22.22.2 | accepted — no error |
| JSON::PP Perl 5.038002 | malformed JSON string, neither array, object, number, string or atom, at character offset 6 (before "Infinity}")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 a JSON value: line 1 column 7 (char 6)what this message means → |
| Ruby JSON.parse Ruby 3.2.3 | unexpected token at ' Infinity}' |
| serde_json::from_str Rust (serde_json 1.x) | expected value at line 1 column 7what this message means → |
| SpiderMonkey JSON.parse SpiderMonkey 115 | JSON.parse: unexpected character at line 1 column 7 of the JSON datawhat this message means → |
| System.Text.Json Deserialize .NET 8.0.30 | 'I' is an invalid start of a value. Path: $ | LineNumber: 0 | BytePositionInLine: 6.what this message means → |
| System.Text.Json JsonDocument .NET 8.0.30 | 'I' is an invalid start of a value. LineNumber: 0 | BytePositionInLine: 6.what this message means → |
| ujson CPython 3.12.3 | accepted — no error |
| V8 JSON.parse Node.js 22.22.2 | Unexpected token 'I', "{"a": Infinity}" is not valid JSONwhat 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. |
| IEEE | Referenced by RFC 8259 §6 as the basis for its interoperability guidance on numbers. |
Peer-reviewed literature
- D. Goldberg, “What every computer scientist should know about floating-point arithmetic”, ACM Computing Surveys, vol. 23, no. 1, pp. 5–48, 1991. doi:10.1145/103162.103163
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