Reproduce the code error with a small sample
Capture the exact error and identify the smallest input that still triggers it. A single identifier, configuration key, or string value is easier to inspect than a complete application. Compare the failing text with an equivalent typed manually in the same environment.
Do not assume AI output is the cause. Code can acquire artifacts through documentation pages, PDFs, chat apps, rich-text editors, or copy-paste between operating systems. The relevant evidence is the actual file and its parsing behavior, not the brand of the tool someone used along the way.
Check hidden characters in syntax, strings, and identifiers
The same character can have different consequences depending on where it appears. A character inside a string may be intentional test data. Outside a string, it may be invalid syntax or part of an identifier under that language’s rules. Comments and documentation examples introduce their own requirements.
A cleaner does not understand every programming language. Do not ask it to decide whether a character is legal in a grammar or meaningful to an application. Inspect the finding, check the language or format specification where needed, and make the narrowest edit that addresses the observed failure.
Detect bidirectional controls and display-order problems
Unicode source-code guidance addresses cases where what a reviewer sees can differ from the logical character sequence. Directional controls are one reason to inspect code beyond its visual appearance. A highlighted control deserves investigation, but its presence alone does not establish malicious intent.
Use your editor’s Unicode or hidden-character display and review the actual sequence around comments, strings, and delimiters. Keep examples escaped or labeled when documenting the issue so someone else can reproduce the finding without accidentally introducing the same invisible character into another file.
Remove unwanted characters with a reviewed code diff
Keep a copy or version-control checkpoint before editing. Turn off prose-oriented transformations such as straightening quotes, replacing dashes, or removing Markdown across a whole source file. Those transformations may change literal data, command options, regular expressions, or examples.
Review the diff after removing the identified artifact. Confirm that indentation, line endings, string contents, and unrelated code did not change. If a file contains intentional invisible-character test cases, preserve them or represent them explicitly using the language’s escape syntax where appropriate.
Validate code after Unicode cleanup
Run a parser or formatter for a syntax problem, a focused test for a behavioral issue, and an import check for structured data. A cleaner reporting success is not enough: it only confirms that its transformation ran. The original failing operation is the best first verification.
If the problem remains, consider encoding, normalization, confusable visible letters, inconsistent identifiers, or an unrelated logic error. Document the minimal reproduction and the verified fix. For recurring incidents, add an editor warning or targeted validation appropriate to the repository rather than silently deleting characters from every future input.
Sources & further reading
Primary references for the technical points in this guide.