System.Text.Json.JsonException: Serialization JSON error for the invalid start of a property name

Issue Description

.NET code serialization using gives an error for a single quote and forces you to use a double quote.

System.Text.Json.JsonException: '''' is an invalid start of a property name. Expected a '"'. Path: $ | LineNumber: 0 | BytePositionInLine: 1.'

or

System.Text.Json.JsonException: “'s' is an invalid start of a value is an invalid start of a property name. Expected a '"'. Path: $ | LineNumber: 0 | BytePositionInLine: 1.' 

Resolution

I had this issue recently for one of the existing codes which was working perfectly fine with NewtonSoft JSON as a serializer.

I was trying to replace Newtonsoft with System.Text.Json.

The issue I found to be due to strict JSON specification usage by Microsoft as per RFC 8259.

Few issues I was able to fix easily by using some options but some issues which I thought Initially, could be fixable but found the limitation on System.Text.Json’s usage.

Reference: RFC 8259 

As per Microsoft,

A value enclosed in single quotes will result in a JsonException. System.Text.Json shall accept property names and string values only in double-quotes as per RFC 8259 specification.

Below JSON sample below are considered in Invalid format,

Invalid Format of JSON

Invalid Format which throws JsonException,

A bellow combination of ” ” and ‘ ‘ representation is not allowed in JSON.

{
  'FirstName': "ABCD"
}

OR

{
  'FirstName': "ABCD"
}

Note- Above both formats however works perfectly fine for Newtonsoft.Json serialization. but you may want to consider that as short term solution ?

Valid Format of JSON

{
  "FirstName": "ABCD"
}

Example

OR

So here although this is not the resolution but rather additional information on the current design and limitation on System.Text.Json usage.

So please plan accordingly… and good luck.

Other scenarios causing “invalid start of a property name”

Comments in JSON fields are not allowed as default behavior while using System.Text.Json.

If you have comments or trailing commas in the JSON, then you might see the above erros.

Example:

{
  "Bank": "Bank of ABCD", //This is Bank Id
  "BranchInfo": [
    {
        "Location": 
          {
            "Street": "address1", //
            "Zip": "Zip",       /*This is zip code*/
            "State": "USA"
          }  
    }
  ]
}

To fix the issue either

• remove comments or
• add a JSON option with a serializer or deserializer to allow the comments.

Please see the below article for more details,

• System.Text.Json – Allow Comments or trailing commas in JSON

Other Useful Reference:

• Serialize and Deserialize using System.Text.Json

• Create Custom Converters for JSON serialization in .NET with example

Did I miss anything else in these resolution steps?

Did the above steps resolve your issue? Please sound off your comments below!

Happy Coding !!

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