Unity-Technologies/UnityCsReference · error · JSONParseException

End of json while parsing while parsing string at {}

Error message

End of json while parsing while parsing string at {}

What it means

Inside ParseString, once a backslash is found the parser increments endidx to read the escape character; if that position is past the end of input (the input ended right after the backslash), it throws JSONParseException ("End of json while parsing while parsing string at <pos>"). The doubled word 'while parsing while parsing' is a typo in the original message but the meaning is a truncated escape sequence.

Source

Thrown at Editor/Mono/AssetStore/Json.cs:537

            while (idx < len)
            {
                int endidx = json.IndexOfAny(endcodes, idx);
                if (endidx < 0)
                    throw new JSONParseException("missing '\"' to end string at " + PosMsg());

                res += json.Substring(idx, endidx - idx);

                if (json[endidx] == '"')
                {
                    cur = json[endidx];
                    idx = endidx;
                    break;
                }

                endidx++; // get escape code
                if (endidx >= len)
                    throw new JSONParseException("End of json while parsing while parsing string at " + PosMsg());

                // char at endidx is \
                char ncur = json[endidx];
                switch (ncur)
                {
                    case '"':
                        goto case '/';
                    case '\\':
                        goto case '/';
                    case '/':
                        res += ncur;
                        break;
                    case 'b':
                        res += '\b';
                        break;
                    case 'f':
                        res += '\f';
                        break;

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Ensure the input is complete and that every backslash is followed by a valid escape character.
2. Validate input length/integrity before parsing.
3. Catch JSONParseException and surface the position to locate the dangling escape.

Example fix

// before
// { "msg": "line1\<EOF>

// after
// { "msg": "line1\nline2" }

// Ensure no input ends mid-escape; read full body before parsing.
// For generated JSON, ensure every backslash is followed by a valid escape char.

try { v = JSON.Parse(json); }
catch (JSONParseException ex) { /* position near dangling backslash */ throw; }

When it happens

Trigger: Truncated input ending immediately after a backslash (e.g. "abc\<EOF>); a malformed escape where the following character was lost; streaming cut mid-escape.

Common situations: Network truncation mid-string; hand-built JSON with a dangling backslash; buffer underrun.

Related errors

• missing '"' to end string at {}
• End of json while parsing while parsing unicode char near {}
• End of json while parsing at {}
• Cannot parse json value starting with '{}' at {}
• Key not string type at {}

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/82d82ff722cf2634. Report an issue: GitHub.