Yes. Remove Duplicate Lines is completely free, with no sign-up, no daily limit, and no watermark on what you download.
No. Remove Duplicate Lines runs entirely in your browser using JavaScript — nothing you type or upload ever leaves your device.
Since processing happens locally in your browser and nothing is sent anywhere, it's as safe as any other action on your own device — but as a habit, avoid pasting real passwords or production secrets into any web tool.
