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.

Reproduce it

The input

Fails to parse

{"a": -}

Parses correctly

{"a": -1}

Open this broken input in the formatter →

The fix

How to fix it

Emit `null` or `0` when the value is missing, and check your template for an unsubstituted placeholder.

Seeing `-` alone is a strong sign of string-concatenation serialisation rather than a real JSON writer.

Cross-runtime

What each parser reports

Every message below was captured by running this exact input through the parser named. 18 of 21 parsers rejected it; 3 accepted it.

Parser	Exact message
CPython json.loads CPython 3.12.3	`Expecting value: line 1 column 7 (char 6)` what this message means →
encoding/json Unmarshal Go go1.22.2	`invalid character '}' in numeric literal` what 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 1,8 >>>"a": -} ...` what this message means →
Jackson ObjectMapper Java 21.0.12	`Unexpected character ('}' (code 125)) in numeric value: expected digit (0-9) to follow minus sign, for valid numeric value` what this message means →
JavaScriptCore JSON.parse JavaScriptCore (Bun 1.4.1)	`JSON Parse error: Invalid number` what this message means →
json-bigint Node.js 22.22.2	`Bad number`
JSON5 Node.js 22.22.2	`JSON5: invalid character '}' at 1:8` what this message means →
JSON::PP Perl 5.038002	`malformed number (no digits after initial minus), at character offset 8 (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	`Input string '-' is not a valid number. Path 'a', line 1, position 7.` what this message means →
Newtonsoft.Json JsonTextReader Newtonsoft.Json 13.0.3 on .NET 8.0.30	`Input string '-' is not a valid number. Path 'a', line 1, position 7.` what this message means →
orjson CPython 3.12.3	`no digit after sign: line 1 column 8 (char 7)` what this message means →
Ruby JSON.parse Ruby 3.2.3	`unexpected token at '{"a": -}'`
serde_json::from_str Rust (serde_json 1.x)	`invalid number at line 1 column 8` what this message means →
SpiderMonkey JSON.parse SpiderMonkey 115	`JSON.parse: unexpected non-digit at line 1 column 8 of the JSON data` what this message means →
System.Text.Json Deserialize .NET 8.0.30	`'}' is invalid within a number, immediately after a sign character ('+' or '-'). Expected a digit ('0'-'9'). Path: $ \| LineNumber: 0 \| BytePositionInLine: 7.` what this message means →
System.Text.Json JsonDocument .NET 8.0.30	`'}' is invalid within a number, immediately after a sign character ('+' or '-'). Expected a digit ('0'-'9'). LineNumber: 0 \| BytePositionInLine: 7.` what this message means →
ujson CPython 3.12.3	accepted — no error
V8 JSON.parse Node.js 22.22.2	`No number after minus sign in JSON at position 7 (line 1 column 8)` what this message means →

Standards

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	RFC 8259 (STD 90) §6 — Numbers 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	ECMA-404, 2nd edition §8 Numbers A number is decimal digits with no superfluous leading zero. Values such as Infinity and NaN are not permitted.

Bare minus sign where a number was expected

The input

How to fix it

What each parser reports

What the specification says

Other errors in this category

Leading zero in a JSON number

Leading plus sign in a JSON number

Trailing decimal point in a JSON number

Leading decimal point in a JSON number

Hexadecimal number in JSON