JamesNK/Newtonsoft.Json · error · JsonException

Array index expected.

Error message

Array index expected.

What it means

Thrown by the JPath array-indexer parser when a comma-separated multi-index list reaches its closing bracket but the segment just parsed has zero length, meaning an index value was expected but missing. This is the multi-index variant at JPath.cs:256-260, triggered when indexes != null and length == 0.

Source

Thrown at Src/Newtonsoft.Json/Linq/JsonPath/JPath.cs:260

            {
                char currentCharacter = _expression[_currentIndex];

                if (currentCharacter == ' ')
                {
                    end = _currentIndex;
                    EatWhitespace();
                    continue;
                }

                if (currentCharacter == indexerCloseChar)
                {
                    int length = (end ?? _currentIndex) - start;

                    if (indexes != null)
                    {
                        if (length == 0)
                        {
                            throw new JsonException("Array index expected.");
                        }

                        string indexer = _expression.Substring(start, length);
                        int index = Convert.ToInt32(indexer, CultureInfo.InvariantCulture);

                        indexes.Add(index);
                        return new ArrayMultipleIndexFilter(indexes);
                    }
                    else if (colonCount > 0)
                    {
                        if (length > 0)
                        {
                            string indexer = _expression.Substring(start, length);
                            int index = Convert.ToInt32(indexer, CultureInfo.InvariantCulture);

                            if (colonCount == 1)
                            {
                                endIndex = index;

View on GitHub (pinned to 4f73e74372)

Solutions

1. Remove the trailing comma so every slot has an integer index, e.g. $[1,2].
2. When constructing index lists programmatically, filter out empty entries before joining with commas.
3. Validate that each comma-separated segment is a non-negative integer.

Example fix

// before
token.SelectToken("$[1,]");

// after
token.SelectToken("$[1]");

// Build a multi-index list, dropping empty entries
var indices = new[] { "1", "", "2" }.Where(s => !string.IsNullOrEmpty(s));
string path = $"$[{string.Join(",", indices)}]";

When it happens

Trigger: A path like token.SelectToken("$[1,]") or "$[,]" where a comma is followed by no digits before the closing ']'. The parser records the comma, then on the ']' finds an empty index segment.

Common situations: Building a multi-index list dynamically and leaving a trailing comma; truncating an index expression; copy/paste leaving an empty slot.

Related errors

• Unexpected character while parsing path indexer:
• Index * not valid on {0}.
• Unexpected character while parsing path:
• Unexpected character following indexer:
• Unexpected end while parsing path.

AI-assisted analysis of JamesNK/Newtonsoft.Json@4f73e74372 (2026-08-07). Data as JSON: /api/errors/ea90aad629004d5d. Report an issue: GitHub.