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Paste a .env file and get every problem listed with its line number. It checks the things that break quietly rather than loudly: duplicate keys where the last one silently wins, unbalanced quotes that swallow the rest of the value, spaces around the equals sign that some loaders keep, unquoted trailing comments, and lines with no equals sign at all.
Dotenv loaders are permissive by design, which means a file can load without error and still not mean what its author thought. Nothing is uploaded — which matters more here than almost anywhere else on the site, because this is the file with all your credentials in it.
Frequently asked questions
Should there be spaces around the equals sign?
No. `KEY=value` is the safe form. Some loaders trim spaces, some keep them as part of the key or the value, and the failure is silent either way — you get a variable named `KEY ` or a value that starts with a space, and spend an hour wondering why the comparison fails.
Do I need to quote values?
Only when the value contains spaces, a `#` you want kept, or characters you don't want interpreted. Quoting is never wrong, though, and it removes a whole class of ambiguity. If your value contains a `#`, quote it — otherwise many loaders treat the rest of the line as a comment.
What happens with duplicate keys?
The last one wins in most loaders, with no warning at all. It's a genuinely nasty bug because both lines look correct in review, and it usually happens when someone appends a variable that already exists further up the file.
Is my .env file uploaded anywhere?
No. Everything is checked in your browser and nothing is transmitted. Given that a .env file typically contains database passwords, API keys and signing secrets, pasting one into any tool that does upload would be a reportable incident.