JSON parser error messages

CPython json.loads CPython 3.12.3

• Expecting ',' delimiter: line L column C (char N)
• Expecting ':' delimiter: line L column C (char N)
• Expecting property name enclosed in double quotes: line L column C (char N)
• Expecting value: line L column C (char N)
• Extra data: line L column C (char N)
• Invalid \escape: line L column C (char N)
• Invalid \uXXXX escape: line L column C (char N)
• Invalid control character at: line L column C (char N)
• Unexpected UTF-8 BOM (decode using utf-8-sig): line L column C (char N)
• Unterminated string starting at: line L column C (char N)

Gson Java 21.0.12

• Expected ':' at line L column C path $…
• Expected name at line L column C path $…
• Invalid escape sequence at line L column C path $…
• Unterminated array at line L column C path $…
• Unterminated object at line L column C path $…
• Unterminated string at line L column C path $…
• Use JsonReader.setLenient(true) to accept malformed JSON at line L column C path $…
• java.io.EOFException: End of input at line L column C path $…

Gson JsonParser (lenient off) Java 21.0.12

• java.lang.NumberFormatException: \u12"}
• java.lang.NumberFormatException: \uZZZZ

JSON5 Node.js 22.22.2

• JSON5: invalid character ',' at 1:2
• JSON5: invalid character ',' at 1:4
• JSON5: invalid character '1' at 1:2
• JSON5: invalid character '1' at 1:6
• JSON5: invalid character '1' at 1:8
• JSON5: invalid character '2' at 1:4
• JSON5: invalid character ':' at 1:3
• JSON5: invalid character '<' at 1:1
• JSON5: invalid character 'T' at 1:7
• JSON5: invalid character 'Z' at 1:10
• JSON5: invalid character '\"' at 1:12
• JSON5: invalid character '\"' at 1:9
• JSON5: invalid character '\n' at 2:0
• JSON5: invalid character 'g' at 1:10
• JSON5: invalid character 'h' at 1:1
• JSON5: invalid character 'h' at 1:7
• JSON5: invalid character 'u' at 1:1
• JSON5: invalid character 'u' at 1:7
• JSON5: invalid character '{' at 1:9
• JSON5: invalid character '{' at 2:1
• JSON5: invalid character '}' at 1:8
• JSON5: invalid character '“' at 1:2
• JSON5: invalid end of input at 1:1
• JSON5: invalid end of input at 1:14
• JSON5: invalid end of input at 1:6
• JSON5: invalid end of input at 1:8
• JSON5: invalid end of input at 2:3

JSON::PP Perl 5.038002

• ':' expected, at character offset N (before "…")
• , or ] expected while parsing array, at character offset N (before "…")
• , or } expected while parsing object/hash, at character offset N (before "…")
• garbage after JSON object, at character offset N (before "…")
• illegal backslash escape sequence in string, at character offset N (before "…")
• invalid character 0x0 encountered while parsing JSON string, at character offset N (before "…")
• invalid character 0x9 encountered while parsing JSON string, at character offset N (before "…")
• invalid character 0xA encountered while parsing JSON string, at character offset N (before "…")
• json text or perl structure exceeds maximum nesting level (max_depth set too low?), at character offset N (before "…")
• malformed JSON string, neither array, object, number, string or atom, at character offset N (before "…")
• malformed number (leading zero must not be followed by another digit), at character offset N (before "…")
• malformed number (no digits after decimal point), at character offset N (before "…")
• malformed number (no digits after initial minus), at character offset N (before "…")
• missing low surrogate character in surrogate pair, at character offset N (before "…")
• unexpected end of string while parsing JSON string, at character offset N (before "…")

Jackson ObjectMapper Java 21.0.12

• Illegal unquoted character ((CTRL-CHAR, code 0)): has to be escaped using backslash to be included in string value
• Illegal unquoted character ((CTRL-CHAR, code 10)): has to be escaped using backslash to be included in string value
• Illegal unquoted character ((CTRL-CHAR, code 9)): has to be escaped using backslash to be included in string value
• Invalid numeric value: Leading zeroes not allowed
• Non-standard token 'Infinity': enable `JsonReadFeature.ALLOW_NON_NUMERIC_NUMBERS` to allow
• Non-standard token 'NaN': enable `JsonReadFeature.ALLOW_NON_NUMERIC_NUMBERS` to allow
• Unexpected character ('"' (code 34)): expected a hex-digit for character escape sequence
• Unexpected character ('"' (code 34)): was expecting comma to separate Object entries
• Unexpected character (''' (code 39)): expected a valid value (JSON String, Number, Array, Object or token 'null', 'true' or 'false')
• Unexpected character (''' (code 39)): was expecting double-quote to start field name
• Unexpected character ('+' (code 43)) in numeric value: JSON spec does not allow numbers to have plus signs: enable `JsonReadFeature.ALLOW_LEADING_PLUS_SIGN_FOR_NUMBERS` to allow
• Unexpected character (',' (code 44)): expected a valid value (JSON String, Number, Array, Object or token 'null', 'true' or 'false')
• Unexpected character (',' (code 44)): was expecting double-quote to start field name
• Unexpected character ('.' (code 46)): expected a valid value (JSON String, Number, Array, Object or token 'null', 'true' or 'false')
• Unexpected character ('/' (code 47)): maybe a (non-standard) comment? (not recognized as one since Feature 'ALLOW_COMMENTS' not enabled for parser)
• Unexpected character ('1' (code 49)): was expecting a colon to separate field name and value
• Unexpected character ('1' (code 49)): was expecting double-quote to start field name
• Unexpected character ('2' (code 50)): was expecting comma to separate Array entries
• Unexpected character (':' (code 58)): was expecting comma to separate Array entries
• Unexpected character ('<' (code 60)): expected a valid value (JSON String, Number, Array, Object or token 'null', 'true' or 'false')
• Unexpected character ('?' (code 65279 / 0xfeff)): expected a valid value (JSON String, Number, Array, Object or token 'null', 'true' or 'false')
• Unexpected character ('?' (code 8220 / 0x201c)): was expecting double-quote to start field name
• Unexpected character ('Z' (code 90)): expected a hex-digit for character escape sequence
• Unexpected character (']' (code 93)): expected a valid value (JSON String, Number, Array, Object or token 'null', 'true' or 'false')
• Unexpected character ('a' (code 97)): was expecting double-quote to start field name
• Unexpected character ('x' (code 120)): was expecting comma to separate Object entries
• Unexpected character ('}' (code 125)) in numeric value: Decimal point not followed by a digit
• Unexpected character ('}' (code 125)) in numeric value: expected digit (0-9) to follow minus sign, for valid numeric value
• Unexpected character ('}' (code 125)): was expecting double-quote to start field name
• Unexpected end-of-input: expected close marker for Array (start marker
• Unexpected end-of-input: expected close marker for Object (start marker
• Unexpected end-of-input: was expecting closing quote for a string value
• Unrecognized character escape 'x' (code 120)
• Unrecognized token 'True': was expecting (JSON String, Number, Array, Object or token 'null', 'true' or 'false')
• Unrecognized token 'hello': was expecting (JSON String, Number, Array, Object or token 'null', 'true' or 'false')
• Unrecognized token 'undefined': was expecting (JSON String, Number, Array, Object or token 'null', 'true' or 'false')

JavaScriptCore JSON.parse JavaScriptCore (Bun 1.4.1)

• JSON Parse error: "\u12"}" is not a valid unicode escape
• JSON Parse error: "\uZZZZ" is not a valid unicode escape
• JSON Parse error: Expected ':' before value in object property definition
• JSON Parse error: Expected ']'
• JSON Parse error: Expected '}'
• JSON Parse error: Invalid digits after decimal point
• JSON Parse error: Invalid escape character x
• JSON Parse error: Invalid number
• JSON Parse error: Property name must be a string literal
• JSON Parse error: Single quotes (') are not allowed in JSON
• JSON Parse error: Unable to parse JSON string
• JSON Parse error: Unexpected EOF
• JSON Parse error: Unexpected comma at the end of array expression
• JSON Parse error: Unexpected identifier "Infinity"
• JSON Parse error: Unexpected identifier "NaN"
• JSON Parse error: Unexpected identifier "True"
• JSON Parse error: Unexpected identifier "hello"
• JSON Parse error: Unexpected identifier "undefined"
• JSON Parse error: Unexpected token ','
• JSON Parse error: Unexpected token '.'
• JSON Parse error: Unrecognized token '+'
• JSON Parse error: Unrecognized token '/'
• JSON Parse error: Unrecognized token '<'
• JSON Parse error: Unrecognized token '“'
• JSON Parse error: Unrecognized token ''
• JSON Parse error: Unterminated string

Newtonsoft.Json JsonConvert Newtonsoft.Json 13.0.3 on .NET 8.0.30

• Additional text encountered after finished reading JSON content: g. Path '', line L, position N.
• Additional text encountered after finished reading JSON content: {. Path '', line L, position N.
• After parsing a value an unexpected character was encountered: ". Path 'a', line L, position N.
• After parsing a value an unexpected character was encountered: 2. Path '[0]', line L, position N.
• Bad JSON escape sequence: \x. Path 'a', line L, position N.
• Input string '-' is not a valid number. Path 'a', line L, position N.
• Invalid Unicode escape sequence: \uZZZZ. Path 'a', line L, position N.
• Invalid character after parsing property name. Expected ':' but got: 1. Path '', line L, position N.
• Invalid property identifier character: ,. Path '', line L, position N.
• Invalid property identifier character: “. Path '', line L, position N.
• The reader's MaxDepth of 64 has been exceeded. Path '[0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0][0]', line L, position N.
• Unexpected character encountered while parsing number: :. Path '', line L, position N.
• Unexpected character encountered while parsing value: +. Path 'a', line L, position N.
• Unexpected character encountered while parsing value: <. Path '', line L, position N.
• Unexpected character encountered while parsing value: T. Path 'a', line L, position N.
• Unexpected character encountered while parsing value: h. Path '', line L, position N.
• Unexpected character encountered while parsing value: h. Path 'a', line L, position N.
• Unexpected character encountered while parsing value: . Path '', line L, position N.
• Unexpected end when deserializing object. Path 'a', line L, position N.
• Unexpected end while parsing Unicode escape sequence. Path 'a', line L, position N.
• Unterminated string. Expected delimiter: ". Path 'a', line L, position N.

Ruby JSON.parse Ruby 3.2.3

• incomplete surrogate pair at '…'
• nesting of 101 is too deep

SpiderMonkey JSON.parse SpiderMonkey 115

• JSON.parse: bad Unicode escape at line L column C of the JSON data
• JSON.parse: bad control character in string literal at line L column C of the JSON data
• JSON.parse: bad escaped character at line L column C of the JSON data
• JSON.parse: end of data after property value in object at line L column C of the JSON data
• JSON.parse: end of data when ',' or ']' was expected at line L column C of the JSON data
• JSON.parse: expected ',' or ']' after array element at line L column C of the JSON data
• JSON.parse: expected ',' or '}' after property value in object at line L column C of the JSON data
• JSON.parse: expected ':' after property name in object at line L column C of the JSON data
• JSON.parse: expected double-quoted property name at line L column C of the JSON data
• JSON.parse: expected property name or '}' at line L column C of the JSON data
• JSON.parse: unexpected character at line L column C of the JSON data
• JSON.parse: unexpected end of data at line L column C of the JSON data
• JSON.parse: unexpected non-digit at line L column C of the JSON data
• JSON.parse: unexpected non-whitespace character after JSON data at line L column C of the JSON data
• JSON.parse: unterminated fractional number at line L column C of the JSON data
• JSON.parse: unterminated string at line L column C of the JSON data

System.Text.Json Deserialize .NET 8.0.30

• '"' is invalid after a value. Expected either ',', '}', or ']'. Path: $ | LineNumber: L | BytePositionInLine: C.
• '"' is not a hex digit following '\u' within a JSON string. The string should be correctly escaped. Path: $ | LineNumber: L | BytePositionInLine: C.
• ''' is an invalid start of a property name. Expected a '"'. Path: $ | LineNumber: L | BytePositionInLine: C.
• ''' is an invalid start of a value. Path: $ | LineNumber: L | BytePositionInLine: C.
• '+' is an invalid start of a value. Path: $ | LineNumber: L | BytePositionInLine: C.
• ',' is an invalid start of a property name. Expected a '"'. Path: $ | LineNumber: L | BytePositionInLine: C.
• ',' is an invalid start of a value. Path: $ | LineNumber: L | BytePositionInLine: C.
• '.' is an invalid start of a value. Path: $ | LineNumber: L | BytePositionInLine: C.
• '/' is invalid after a value. Expected either ',', '}', or ']'. Path: $ | LineNumber: L | BytePositionInLine: C.
• '0x00' is invalid within a JSON string. The string should be correctly escaped. Path: $ | LineNumber: L | BytePositionInLine: C.
• '0x09' is invalid within a JSON string. The string should be correctly escaped. Path: $ | LineNumber: L | BytePositionInLine: C.
• '0x0A' is invalid within a JSON string. The string should be correctly escaped. Path: $ | LineNumber: L | BytePositionInLine: C.
• '0xE2' is an invalid start of a property name. Expected a '"'. Path: $ | LineNumber: L | BytePositionInLine: C.
• '0xEF' is an invalid start of a value. Path: $ | LineNumber: L | BytePositionInLine: C.
• '1' is an invalid end of a number. Expected a delimiter. Path: $ | LineNumber: L | BytePositionInLine: C.
• '1' is an invalid start of a property name. Expected a '"'. Path: $ | LineNumber: L | BytePositionInLine: C.
• '1' is invalid after a property name. Expected a ':'. Path: $ | LineNumber: L | BytePositionInLine: C.
• '2' is an invalid end of a number. Expected a delimiter. Path: $ | LineNumber: L | BytePositionInLine: C.
• '2' is invalid after a value. Expected either ',', '}', or ']'. Path: $ | LineNumber: L | BytePositionInLine: C.
• ':' is an invalid end of a number. Expected a delimiter. Path: $ | LineNumber: L | BytePositionInLine: C.
• '<' is an invalid start of a value. Path: $ | LineNumber: L | BytePositionInLine: C.
• 'I' is an invalid start of a value. Path: $ | LineNumber: L | BytePositionInLine: C.
• 'N' is an invalid start of a value. Path: $ | LineNumber: L | BytePositionInLine: C.
• 'T' is an invalid start of a value. Path: $ | LineNumber: L | BytePositionInLine: C.
• 'Z' is not a hex digit following '\u' within a JSON string. The string should be correctly escaped. Path: $ | LineNumber: L | BytePositionInLine: C.
• 'a' is an invalid start of a property name. Expected a '"'. Path: $ | LineNumber: L | BytePositionInLine: C.
• 'g' is invalid after a single JSON value. Expected end of data. Path: $ | LineNumber: L | BytePositionInLine: C.
• 'h' is an invalid start of a value. Path: $ | LineNumber: L | BytePositionInLine: C.
• 'u' is an invalid start of a value. Path: $ | LineNumber: L | BytePositionInLine: C.
• 'x' is an invalid end of a number. Expected a delimiter. Path: $ | LineNumber: L | BytePositionInLine: C.
• 'x' is an invalid escapable character within a JSON string. The string should be correctly escaped. Path: $ | LineNumber: L | BytePositionInLine: C.
• '{' is invalid after a single JSON value. Expected end of data. Path: $ | LineNumber: L | BytePositionInLine: C.
• '}' is invalid within a number, immediately after a decimal point ('.'). Expected a digit ('0'-'9'). Path: $ | LineNumber: L | BytePositionInLine: C.
• '}' is invalid within a number, immediately after a sign character ('+' or '-'). Expected a digit ('0'-'9'). Path: $ | LineNumber: L | BytePositionInLine: C.
• Expected end of string, but instead reached end of data. Path: $ | LineNumber: L | BytePositionInLine: C.
• Invalid leading zero before '1'. Path: $ | LineNumber: L | BytePositionInLine: C.
• 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.
• The input does not contain any JSON tokens. Expected the input to start with a valid JSON token, when isFinalBlock is true. Path: $ | LineNumber: L | BytePositionInLine: C.
• The maximum configured depth of 64 has been exceeded. Cannot read next JSON array. Path: $ | LineNumber: L | BytePositionInLine: C.

System.Text.Json JsonDocument .NET 8.0.30

• '"' is invalid after a value. Expected either ',', '}', or ']'. LineNumber: L | BytePositionInLine: C.
• '"' is not a hex digit following '\u' within a JSON string. The string should be correctly escaped. LineNumber: L | BytePositionInLine: C.
• ''' is an invalid start of a property name. Expected a '"'. LineNumber: L | BytePositionInLine: C.
• ''' is an invalid start of a value. LineNumber: L | BytePositionInLine: C.
• '+' is an invalid start of a value. LineNumber: L | BytePositionInLine: C.
• ',' is an invalid start of a property name. Expected a '"'. LineNumber: L | BytePositionInLine: C.
• ',' is an invalid start of a value. LineNumber: L | BytePositionInLine: C.
• '.' is an invalid start of a value. LineNumber: L | BytePositionInLine: C.
• '/' is invalid after a value. Expected either ',', '}', or ']'. LineNumber: L | BytePositionInLine: C.
• '0x00' is invalid within a JSON string. The string should be correctly escaped. LineNumber: L | BytePositionInLine: C.
• '0x09' is invalid within a JSON string. The string should be correctly escaped. LineNumber: L | BytePositionInLine: C.
• '0x0A' is invalid within a JSON string. The string should be correctly escaped. LineNumber: L | BytePositionInLine: C.
• '0xE2' is an invalid start of a property name. Expected a '"'. LineNumber: L | BytePositionInLine: C.
• '0xEF' is an invalid start of a value. LineNumber: L | BytePositionInLine: C.
• '1' is an invalid end of a number. Expected a delimiter. LineNumber: L | BytePositionInLine: C.
• '1' is an invalid start of a property name. Expected a '"'. LineNumber: L | BytePositionInLine: C.
• '1' is invalid after a property name. Expected a ':'. LineNumber: L | BytePositionInLine: C.
• '2' is an invalid end of a number. Expected a delimiter. LineNumber: L | BytePositionInLine: C.
• '2' is invalid after a value. Expected either ',', '}', or ']'. LineNumber: L | BytePositionInLine: C.
• ':' is an invalid end of a number. Expected a delimiter. LineNumber: L | BytePositionInLine: C.
• '<' is an invalid start of a value. LineNumber: L | BytePositionInLine: C.
• 'I' is an invalid start of a value. LineNumber: L | BytePositionInLine: C.
• 'N' is an invalid start of a value. LineNumber: L | BytePositionInLine: C.
• 'T' is an invalid start of a value. LineNumber: L | BytePositionInLine: C.
• 'Z' is not a hex digit following '\u' within a JSON string. The string should be correctly escaped. LineNumber: L | BytePositionInLine: C.
• 'a' is an invalid start of a property name. Expected a '"'. LineNumber: L | BytePositionInLine: C.
• 'g' is invalid after a single JSON value. Expected end of data. LineNumber: L | BytePositionInLine: C.
• 'h' is an invalid start of a value. LineNumber: L | BytePositionInLine: C.
• 'u' is an invalid start of a value. LineNumber: L | BytePositionInLine: C.
• 'x' is an invalid end of a number. Expected a delimiter. LineNumber: L | BytePositionInLine: C.
• 'x' is an invalid escapable character within a JSON string. The string should be correctly escaped. LineNumber: L | BytePositionInLine: C.
• '{' is invalid after a single JSON value. Expected end of data. LineNumber: L | BytePositionInLine: C.
• '}' is invalid within a number, immediately after a decimal point ('.'). Expected a digit ('0'-'9'). LineNumber: L | BytePositionInLine: C.
• '}' is invalid within a number, immediately after a sign character ('+' or '-'). Expected a digit ('0'-'9'). LineNumber: L | BytePositionInLine: C.
• Expected end of string, but instead reached end of data. LineNumber: L | BytePositionInLine: C.
• Invalid leading zero before '1'. LineNumber: L | BytePositionInLine: C.
• 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.
• The input does not contain any JSON tokens. Expected the input to start with a valid JSON token, when isFinalBlock is true. LineNumber: L | BytePositionInLine: C.
• The maximum configured depth of 64 has been exceeded. Cannot read next JSON array. LineNumber: L | BytePositionInLine: C.

V8 JSON.parse Node.js 22.22.2

• "undefined" is not valid JSON
• Bad Unicode escape in JSON at position N (line L column C)
• Bad control character in string literal in JSON at position N (line L column C)
• Bad escaped character in JSON at position N (line L column C)
• Expected ',' or ']' after array element in JSON at position N (line L column C)
• Expected ',' or '}' after property value in JSON at position N (line L column C)
• Expected ':' after property name in JSON at position N (line L column C)
• Expected double-quoted property name in JSON at position N (line L column C)
• Expected property name or '}' in JSON at position N (line L column C)
• No number after minus sign in JSON at position N (line L column C)
• Unexpected end of JSON input
• Unexpected non-whitespace character after JSON at position N (line L column C)
• Unexpected number in JSON at position N (line L column C)
• Unexpected token ''', "'{"a": 1}'" is not valid JSON
• Unexpected token '+', "{"a": +1}" is not valid JSON
• Unexpected token ',', "[1,,2]" is not valid JSON
• Unexpected token '.', "{"a": .5}" is not valid JSON
• Unexpected token '<', "…"... is not valid JSON
• Unexpected token 'I', "{"a": Infinity}" is not valid JSON
• Unexpected token 'N', "{"a": NaN}" is not valid JSON
• Unexpected token 'T', "{"a": True, "b"…"... is not valid JSON
• Unexpected token ']', "[1, 2, 3,]" is not valid JSON
• Unexpected token 'h', "hello" is not valid JSON
• Unexpected token 'h', "{"a": hello}" is not valid JSON
• Unexpected token 'u', "{"a": undefined}" is not valid JSON
• Unexpected token '', "{"a": 1}" is not valid JSON
• Unterminated fractional number in JSON at position N (line L column C)
• Unterminated string in JSON at position N (line L column C)

encoding/json Unmarshal Go go1.22.2

• invalid character '"' after object key:value pair
• invalid character '"' in \u hexadecimal character escape
• invalid character '+' looking for beginning of value
• invalid character ',' looking for beginning of object key string
• invalid character ',' looking for beginning of value
• invalid character '.' looking for beginning of value
• invalid character '/' looking for beginning of object key string
• invalid character '1' after object key
• invalid character '1' after object key:value pair
• invalid character '1' looking for beginning of object key string
• invalid character '2' after array element
• invalid character ':' after array element
• invalid character '<' looking for beginning of value
• invalid character 'I' looking for beginning of value
• invalid character 'N' looking for beginning of value
• invalid character 'T' looking for beginning of value
• invalid character 'Z' in \u hexadecimal character escape
• invalid character '\'' looking for beginning of object key string
• invalid character '\'' looking for beginning of value
• invalid character '\n' in string literal
• invalid character '\t' in string literal
• invalid character '\x00' in string literal
• invalid character ']' looking for beginning of value
• invalid character 'a' looking for beginning of object key string
• invalid character 'g' after top-level value
• invalid character 'h' looking for beginning of value
• invalid character 'u' looking for beginning of value
• invalid character 'x' after object key:value pair
• invalid character 'x' in string escape code
• invalid character '{' after top-level value
• invalid character '}' after decimal point in numeric literal
• invalid character '}' in numeric literal
• invalid character '}' looking for beginning of object key string
• invalid character 'â' looking for beginning of object key string
• invalid character 'ï' looking for beginning of value
• unexpected end of JSON input

hjson Node.js 22.22.2

• Bad \u char " at line L,11
• Bad \u char Z at line L,9
• Bad string at line L,10
• Bad string at line L,13
• Bad string containing newline at line L,0
• End of input while parsing an array (missing ']') at line L,5
• End of input while parsing an array (missing ']') at line L,6
• End of input while parsing an object (missing '}') at line L,10
• End of input while parsing an object (missing '}') at line L,11
• End of input while parsing an object (missing '}') at line L,12
• End of input while parsing an object (missing '}') at line L,15
• End of input while parsing an object (missing '}') at line L,16
• End of input while parsing an object (missing '}') at line L,22
• End of input while parsing an object (missing '}') at line L,7
• End of input while parsing an object (missing '}') at line L,8
• End of input while parsing an object (missing '}') at line L,9
• Expected ':' instead of '1' at line L,5
• Found ',' where a key name was expected (check your syntax or use quotes if the key name includes {}[],: or whitespace) at line L,1
• Found EOF while looking for a key name (check your syntax) at line L,30
• Found a punctuator character ',' when expecting a quoteless string (check your syntax) at line L,3
• Syntax error, found trailing characters at line L,1 >>>{"a":2} {"a":3} ...
• Syntax error, found trailing characters at line L,8
• Syntax error, found trailing characters at line L,9

json-bigint Node.js 22.22.2

• Expected ',' instead of '"'
• Expected ',' instead of ''
• Expected ',' instead of '2'
• Expected ',' instead of ':'
• Expected ',' instead of 'x'
• Expected ':' instead of '1'

json_decode PHP 8.3.6

• Maximum stack depth exceeded
• Single unpaired UTF-16 surrogate in unicode escape

orjson CPython 3.12.3

• Input is a zero-length, empty document: line L column C (char N)
• UTF-8 byte order mark (BOM) is not supported: line L column C (char N)
• input data is empty: line L column C (char N)
• invalid escaped sequence in string: line L column C (char N)
• no digit after decimal point: line L column C (char N)
• no digit after sign: line L column C (char N)
• no low surrogate in string: line L column C (char N)
• number with leading zero is not allowed: line L column C (char N)
• trailing comma is not allowed: line L column C (char N)
• unexpected character, expected ',' or ']': line L column C (char N)
• unexpected character, expected ',' or '}': line L column C (char N)
• unexpected character, expected ':' after key: line L column C (char N)
• unexpected character, expected a JSON value: line L column C (char N)
• unexpected character, expected a string key: line L column C (char N)
• unexpected content after document: line L column C (char N)
• unexpected control character in string: line L column C (char N)
• unexpected end of data: line L column C (char N)

serde_json::from_str Rust (serde_json 1.x)

• EOF while parsing a list at line L column C
• EOF while parsing a string at line L column C
• EOF while parsing a value at line L column C
• EOF while parsing an object at line L column C
• control character (\u0000-\u001F) found while parsing a string at line L column C
• expected `,` or `]` at line L column C
• expected `,` or `}` at line L column C
• expected `:` at line L column C
• expected value at line L column C
• invalid escape at line L column C
• invalid number at line L column C
• key must be a string at line L column C
• recursion limit exceeded at line L column C
• trailing characters at line L column C
• trailing comma at line L column C
• unexpected end of hex escape at line L column C

ujson CPython 3.12.3

• Key name of object must be 'string' when decoding 'object'
• No ':' found when decoding object value
• Unexpected character found when decoding array value (1)
• Unexpected character found when decoding array value (2)
• Unexpected character in found when decoding object value
• Unexpected character in unicode escape sequence when decoding 'string'
• Unmatched '"' when decoding 'string'
• Unrecognized escape sequence when decoding 'string'

50 malformed JSON documents were each passed to 21 parsers, and the resulting exception message was recorded verbatim along with the runtime version. That produced 1050 observations and 563 distinct raw messages, which collapse to 401 message signatures once byte offsets and line numbers are templated.

Parsers covered: CPython json.loads, Gson, Gson JsonParser (lenient off), JSON5, JSON::PP, Jackson ObjectMapper, JavaScriptCore JSON.parse, Newtonsoft.Json JsonConvert, Newtonsoft.Json JsonTextReader, Ruby JSON.parse, SpiderMonkey JSON.parse, System.Text.Json Deserialize, System.Text.Json JsonDocument, V8 JSON.parse, encoding/json Unmarshal, hjson, json-bigint, json_decode, orjson, serde_json::from_str, ujson — across 12 runtimes.

All three major browser engines are covered — V8 (Chrome, Edge, Node), SpiderMonkey (Firefox) and JavaScriptCore (Safari) — because a developer searches whatever their browser said, and the three word the same failure completely differently.

Documented gap: older runtime versions. V8 changed its JSON error wording in Node 20, and the earlier phrasing (Unexpected token } in JSON at position 8) is still widely searched. Every observation here records the exact runtime version it came from, so a message-by-version matrix is the natural next step.