Overview
Paste a JavaScript snippet and check whether it parses as valid syntax - without ever executing it. This works by constructing a Function from your source (the standard, well-understood technique for safe syntax-only checking) and immediately discarding it unread: compiling code is not the same as running it, and the function this tool builds is never called anywhere, so nothing in the pasted code executes no matter what it contains. No eval is used anywhere in this tool. Modern syntax - arrow functions, template literals, optional chaining, nullish coalescing, and both comment styles - is checked using the browser's own JavaScript engine, so support tracks whatever the browser you're using already understands. A syntax error is reported with the engine's own error message and, where available, the line it was found near.
Best for: Checking a pasted code snippet for a syntax error before debugging further
How to use this tool
- Paste a JavaScript snippet. A function body, script, or code block you want to check for syntax errors.
- The code is compiled, never run. A Function is constructed from the source and immediately discarded - it is never called.
- Errors surface with a message. A syntax error is reported using the browser engine's own error message.
- Valid code is confirmed instantly. No syntax errors means the snippet is confirmed as parseable JavaScript.
Why use this tool
No eval, ever
This tool never calls eval - syntax checking uses the Function constructor instead.
Constructed, never invoked
The function built from your code is thrown away unread and is never executed.
Understands modern syntax
Arrow functions, template literals, optional chaining, and nullish coalescing are all checked correctly.
Fully client-side
Nothing you paste is sent anywhere - checking happens entirely in your browser.
Frequently asked questions
No. The code is compiled by constructing a Function from it, which parses and validates syntax exactly like eval would, but the resulting function is never invoked - it's discarded immediately after construction. No side effect in your code, such as a network call or a console log, will ever run here.
No - the JavaScript Formatter reformats already-valid code for readability and doesn't check syntax on its own. This tool does the opposite job: it only checks whether code parses correctly and reports a syntax error if it doesn't, without reformatting anything.
Top-level import and export statements are only valid inside an ES module, not inside a plain function body, which is the context this tool checks code in. Paste just the function or script logic (without the module-level import/export lines) to validate that part on its own.