JamesNK/Newtonsoft.Json · error · ArgumentException

Invalid JavaScript string quote character. Valid quote chara

Error message

Invalid JavaScript string quote character. Valid quote characters are ' and ".

What it means

Thrown by the JsonTextWriter.QuoteChar setter when assigning a character other than double-quote (") or single-quote ('). Valid JSON permits only these two as string/property delimiters, so any other char (backtick, space, etc.) is rejected with ArgumentException at configuration time rather than producing malformed output.

Source

Thrown at Src/Newtonsoft.Json/JsonTextWriter.cs:114

                {
                    throw new ArgumentException("Indentation value must be greater than 0.");
                }

                _indentation = value;
            }
        }

        /// <summary>
        /// Gets or sets which character to use to quote attribute values.
        /// </summary>
        public char QuoteChar
        {
            get => _quoteChar;
            set
            {
                if (value != '"' && value != '\'')
                {
                    throw new ArgumentException(@"Invalid JavaScript string quote character. Valid quote characters are ' and "".");
                }

                _quoteChar = value;
                UpdateCharEscapeFlags();
            }
        }

        /// <summary>
        /// Gets or sets which character to use for indenting when <see cref="JsonWriter.Formatting"/> is set to <see cref="Formatting.Indented"/>.
        /// </summary>
        public char IndentChar
        {
            get => _indentChar;
            set
            {
                if (value != _indentChar)
                {
                    _indentChar = value;

View on GitHub (pinned to 4f73e74372)

Solutions

1. Use '"' (default, maximally compatible) or '\'' for single-quoted output.
2. Validate config before assignment: if (c == '\"' || c == '\'') writer.QuoteChar = c;.
3. For single-quoted JS-style output set both QuoteChar='\'' and StringEscapeHandling.EscapeSingleQuotes (as appropriate).

Example fix

// before
writer.QuoteChar = '`';

// after
writer.QuoteChar = '"';

if (configuredQuote == '"' || configuredQuote == '\'')
{
    writer.QuoteChar = configuredQuote;
}

static bool IsValidQuoteChar(char c) => c == '"' || c == '\'';

When it happens

Trigger: Setting writer.QuoteChar to any char except " or '; reading QuoteChar from config as a char/string and assigning an invalid value; passing a unicode whitespace or punctuation char.

Common situations: Config that supplies a wrong quote character; interop code assuming backticks are valid; parsing a 'quote style' setting into a char incorrectly.

Related errors

• Indentation value must be greater than 0.
• An ObjectId must be 12 bytes
• Cannot convert date value that is before Unix epoch of 00:00
• Namespace attribute must have a value.
• Delimiter must be a single or double quote.

AI-assisted analysis of JamesNK/Newtonsoft.Json@4f73e74372 (2026-08-07). Data as JSON: /api/errors/dc5c6688ce63ed9a. Report an issue: GitHub.