Run your JavaScript through ESLint, the linter used by most professional teams, without installing Node.js. It finds syntax errors, variables used before they exist, unused variables, = instead of === in an if, unreachable code, duplicate keys and other mistakes that cause bugs, with the line and the rule name for each one.
loading toolHow to use the javascript checker (eslint)
- Paste your code into the box (or tap Try a sample).
- Read the list of problems: ✕ marks an error, ! a warning.
- Tap Show next to a problem to jump to that line, fix it, and watch the list update.
Good to know
- Search the rule name shown in brackets (for example “no-undef eslint”) to read why it matters.
- A “Parsing error” means the code cannot run at all: fix it before the others.
Questions
Which rules are used?
The rules that catch real bugs are errors (like no-undef, no-const-assign, no-unreachable and no-dupe-keys). Risky habits are warnings (like no-unused-vars and no-eval). Tick “Also check style” to add ===, const, curly braces and console warnings.
Why are window and document allowed?
Browser mode knows every global your browser has. Pick Node.js to allow require and module, or ES module for import and export.
Does my code get uploaded?
No. The checker or runtime is downloaded once from a public CDN (jsDelivr or cdnjs) and then runs inside your browser. Your code never leaves your device.
Is my data private?
Yes. Everything happens inside your own browser: nothing you type or choose is uploaded to us or anyone else.
Is it free?
Completely free, with no sign-up, no watermark and no limit on how many times you use it. Light ads keep the site running.
