stride3d/stride · error · SyntaxErrorException

While scanning a %TAG directive, did not find expected…

Error message

While scanning a %TAG directive, did not find expected whitespace.

What it means

Thrown by the YAML Scanner when, after scanning the handle of a %TAG directive, the next character is not a whitespace. A %TAG directive must separate its handle and prefix with whitespace, e.g. '%TAG ! tag:example.com,2000:'.

Solutions

Insert a space between the tag handle and the tag URI prefix: '%TAG !e! tag:example.com,2000:'.
Remove the %TAG directive if tag shorthand is not needed and use full tag URIs inline.
Check for missing spaces caused by aggressive whitespace stripping in a build/minify step.
Validate the file with yamllint or an online YAML parser before deployment.

Example fix

// before
%TAG!e!tag:example.com,2000:
---
// after
%TAG !e! tag:example.com,2000:
---

Defensive patterns

Strategy: validation

Validate before calling

bool IsValidTagDirective(string line) =>
    !line.StartsWith("%TAG") ||
    System.Text.RegularExpressions.Regex.IsMatch(line, "^%TAG\\s+!?[!A-Za-z0-9-]*!\\s+\\S+");

Try / catch

try
{
    var obj = Deserializer.FromText(yaml);
}
catch (SyntaxErrorException ex)
{
    Log.Error(ex, "Missing whitespace in %TAG directive at line {Line}", ex.Start.Line);
    throw;
}

Prevention

Keep a space between handle and prefix: '%TAG !e! tag:example.com,2000:'
Avoid whitespace-stripping/minification steps on YAML files
Validate tag directives with a reference parser before deployment

When it happens

Trigger: Parsing YAML with a %TAG directive missing the space between handle and prefix, e.g. '%TAG!!foo:' or '%TAG!e!tag:example.com'.

Common situations: Minified or hand-compressed YAML where spaces were stripped; typos merging the handle with the prefix; generated tag directives from buggy writers.

Related errors

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/3c96d93c303c44d6. Report an issue: GitHub.

Appendix: source

Thrown at sources/core/Stride.Core.Yaml/Scanner.cs:2085

        /// Scan the value of a TAG-DIRECTIVE token.
        ///
        /// Scope:
        ///      %TAG    !yaml!  tag:yaml.org,2002:  \n
        ///          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        /// </summary>
        private Token ScanTagDirectiveValue(Mark start)
        {
            SkipWhitespaces();

            // Scan a handle.

            string handle = ScanTagHandle(true, start);

            // Expect a whitespace.

            if (!analyzer.IsBlank())
            {
                throw new SyntaxErrorException(start, mark, "While scanning a %TAG directive, did not find expected whitespace.");
            }

            SkipWhitespaces();

            // Scan a prefix.

            string prefix = ScanTagUri(null, start);

            // Expect a whitespace or line break.

            if (!analyzer.IsBlankOrBreakOrZero())
            {
                throw new SyntaxErrorException(start, mark, "While scanning a %TAG directive, did not find expected whitespace or line break.");
            }

            return new TagDirective(handle, prefix, start, start);
        }

View on GitHub (pinned to 96fad776d2)