Syntax Validation Tools
JavaScript Validator
Parse JavaScript as a modern ECMAScript module and report syntax errors with line and column positions.
✓ Every tool runs in your browser. We do not upload your input or output.
Keyboard shortcuts
Ctrl/⌘ + Enter: process
Ctrl/⌘ + Shift + F: full screen
Esc: exit full screen
Ctrl/⌘ + F in editor: search
How to use
- Paste JavaScript source into the editor.
- Run validation and inspect any highlighted syntax error.
- Fix the source and run it again until parsing succeeds.
- Use your project build and tests to check types and runtime behavior afterward.
Examples
Check a reducer
This parses successfully, but items must still exist at runtime.
const total = items.reduce((sum, item) => sum + item.price, 0);
Valid JavaScript syntax
Separate syntax from behavior
A parser can quickly identify a missing bracket, unexpected token, or invalid expression. This tool uses a JavaScript parser in the browser’s processing worker and reports its location. It treats the input as an ECMAScript module, so imports and exports are valid. It does not evaluate the code. That makes it appropriate for checking an unfamiliar snippet without running its side effects.
Successful parsing does not mean the program is safe or correct. Names may be undefined, a function may return the wrong value, and browser or Node APIs may be unavailable in the target environment. Use your normal type checker, linter, tests, and build for those questions. Paste a focused function or a full file to locate a syntax problem; the workspace handles large source with internal scrolling and keeps the code on your device.
When checking a pasted snippet, include enough surrounding syntax to keep it meaningful. A method body alone may fail to parse as a module even when it is valid inside a class. Wrap it in its original declaration or test the complete source file.
Frequently asked questions
Does this execute the code?
No. It only parses source and never runs the program.
Does it type-check TypeScript?
No. TypeScript syntax requires a separate TypeScript compiler.
Are undefined variables detected?
No. A parser does not perform scope analysis or runtime checks.
Why does a script tag behave differently?
This tool parses module syntax, which has different rules from some classic scripts.