Syntax Checker

Paste code below. We detect the language and check whether it parses — entirely in your browser. Nothing you paste is sent anywhere; the check runs locally, in your browser's own memory.

Supported languages

JavaScript, TypeScript, Python, Java, C#, C++, C, Go, Rust, PHP, Ruby, Swift, Kotlin, Bash/Shell, and SQL — chosen from today's most widely used languages. Upload a file and we use its extension; for pasted code with no filename, detection is heuristic based on common syntax markers, and you can always pick the language manually.

How this works

Everything runs in your browser, in local memory, using a tokenizer and checker we built ourselves — no third-party parsing library is used.
This checks structural syntax: unterminated strings or comments, unmatched or mismatched brackets, and (for Python) indentation consistency. It does not run your code, and it does not validate full language grammar, keyword usage, or types — some invalid code may still pass, and this is not a substitute for a real compiler or linter.