Does this send my code anywhere?

No. Validation runs entirely in your browser.

Does this catch logic bugs?

No. It only checks whether the code parses as syntactically valid JavaScript, not whether it behaves correctly.

Does it support TypeScript?

No. It uses the same Babel-based parser as the JavaScript Formatter, which handles standard JavaScript (including JSX and ES modules) but not TypeScript-only syntax like type annotations or interfaces.

Does it check for undeclared variables or unreachable code?

No. It's a pure syntax check; catching undeclared variables, unused code, or style issues requires a linter like ESLint, not a parser.

JavaScript Validator - Check JS Syntax Online

Overview

Introduction

Before pasting a JavaScript snippet into a project, it's useful to confirm it actually parses without errors.

This tool checks JavaScript syntax entirely in your browser and reports the exact location of the first problem, if any.

What Is JavaScript Validator?

A syntax validator that parses your code with Prettier's Babel-based JavaScript parser and reports success or the first parse error.

It answers one question: does this parse as valid JavaScript, not whether it's well-written or bug-free.

How JavaScript Validator Works

The parser attempts to build a syntax tree from your input.

If parsing succeeds, the code is valid; if it fails, the parser's own error, including line and column, is shown.

When To Use JavaScript Validator

Use it when you're not sure whether a pasted snippet is complete or has a stray syntax error, before spending time debugging elsewhere.

It's also useful for a quick pass/fail check on LLM-generated or copy-pasted JavaScript before adding it to a project.

Often used alongside JavaScript Formatter and JavaScript Minifier.

Features

Advantages

Runs entirely client-side.
Reports the exact line and column of the first syntax problem.
Uses the same Babel-based parser as the JavaScript Formatter, so a 'valid' result is one you can trust to also format cleanly.

Limitations

Only checks syntax, not logic, type correctness, or runtime behavior.
ES module `import`/`export` syntax is supported since the same parser used by the formatter is used here.

Examples

Missing closing brace

Input

function greet(name) {
  return name;

Output

Unexpected token (2:14)

The parser reports exactly where it expected a closing brace that never arrived.

Best Practices & Notes

Best Practices

Use this before the JavaScript Formatter when you specifically want a fast pass/fail syntax check without reformatting anything.
If validation fails on a .ts file, strip TypeScript-only syntax first or check it with a tool that understands TypeScript, since this parser only handles standard JavaScript.

Developer Notes

Reuses the same Prettier `babel` parser as the JavaScript Formatter; the input is discarded on success and only the parse result matters.

JavaScript Validator Use Cases

Confirming a pasted snippet is complete and syntactically valid
Quickly checking a generated or LLM-produced script before running it

Common Mistakes

Assuming a 'valid' result means the code is bug-free; it only confirms the syntax parses.
Pasting TypeScript source and expecting type errors to surface; TypeScript-only syntax isn't part of what this parser checks.

Tips

If validation fails unexpectedly, check for a stray character copied along with the code, like a trailing backtick or smart quote.
For undeclared variables, unused code, or style issues beyond syntax, follow up with a linter like ESLint.

JavaScript Validator