Paste some code on the left — it validates as you type.
JavaScript Validator
Real ES2024 parsing — no false errors on modern code.
About the JavaScript Validator
What is a JavaScript validator?
A JavaScript validator answers one question with certainty: will an engine parse this code? A single unbalanced bracket, a comma where a value should be, or a broken template literal means the whole file throws before a single line runs. This tool parses your code live with the same parser that powers Terser — the minifier inside Vite, Rollup, and webpack builds — and reports the first syntax error with its exact line, column, and a code frame pointing at the character where parsing failed.
The reason this rebuild matters is false errors. Older online validators run linters frozen years ago, which reject optional chaining, class fields, static blocks, private #members, BigInt, and top-level await — all standard JavaScript today. This validator's parser speaks current ECMAScript, auto-detects whether your code is a script or an ES module (and tries both, so top-level await never trips it), and tells you which one it parsed. If it says your code is valid, a browser will agree. Everything runs in a background worker in your browser; nothing is uploaded.
How to Use This Tool
- Add your JavaScript. Paste it into the left editor, click Open file, or try the Valid and Broken samples.
- Read the badge. Green shows valid, plus whether it parsed as a script or an ES module.
- Click the error. The editor jumps to the exact line and column where parsing failed.
- Fix and repeat. Validation re-runs as you type; parsers stop at the first syntax error, so fix it and the next one (if any) appears.
Common Use Cases
- Pinpointing "Unexpected token": The browser console names the symptom; this shows the exact spot with context.
- Checking pasted or generated code: Verify a snippet from an article, an AI, or a code generator before it enters your project.
- Validating without a build step: Sanity-check hand-edited scripts on sites that have no bundler or CI.
- Confirming module vs script issues: See instantly whether code needs to load as an ES module.
Valid but messy? The JavaScript Formatter beautifies it and the JavaScript Minifier compresses it with the same Terser engine. Or browse all our free developer tools.
Frequently Asked Questions
Does it support the latest JavaScript syntax?
Yes. Optional chaining, nullish coalescing and assignment operators, class fields and static blocks, private #members, BigInt, numeric separators, async generators, and top-level await all validate correctly — the parser is the same one modern build tools rely on.
Is this a linter like ESLint?
No, and that's deliberate. Linters mix style opinions with correctness and need per-project configuration; this tool checks one objective thing — whether the code parses — and is never wrong about it. For style and best-practice rules, run ESLint with your project's own config.
Why does it show only one error at a time?
Because JavaScript parsers genuinely stop at the first syntax error — anything "found" beyond it is guesswork, and tools that guess routinely send you chasing phantom errors. Fix the real one, and the next (if any) appears instantly.
What does "parsed as a module" mean?
ES modules (import/export, top-level await) have slightly different parsing rules from classic scripts. The validator auto-detects the right mode and tries the other one before reporting failure, then tells you which succeeded — useful when code works in a <script type="module"> but not a plain <script>.
Can it validate TypeScript or JSX?
No — type annotations and JSX aren't JavaScript syntax, so they'll be reported as errors. Validate the compiled output instead, which is what actually runs.
Is my code uploaded anywhere?
No. Parsing happens in a web worker in your browser with a locally served parser — no CDN, no server round trips, no logging. It even works offline once the page has loaded.