List Compare

Compare, dedupe & diff two lists — right in your browser.
Set operations (A ∩ B, A-only, B-only), duplicate detection, and Jaccard similarity.
Fast, private, zero-upload, and a single HTML file with no dependencies.

▶ Live demo · Features · Usage · Privacy

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Paste two lists and instantly see how they overlap: what's in both, what's only in A, what's only in B, the duplicates inside each, and an overall similarity score. Everything runs locally in your browser — your lists are never uploaded anywhere.

Features

• Set operations — intersection (A ∩ B), A-only, B-only, and union, computed live.
• Deduplicate — collapse repeats within a list, and surface the duplicate entries.
• Similarity — unique counts per list, items in common, and Jaccard similarity %.
• Normalization — ignore case and trim whitespace so " Apple" and "apple" match when you want.
• Sort / shuffle / swap — reorder either list, or swap A ↔ B in one click.
• Import & export — drag-and-drop a .txt file onto a list; download any result as .txt; one-click copy.
• Autosave — your lists are remembered locally (localStorage) between visits.
• Keyboard — Ctrl/⌘ + Enter to compare.
• Light & dark theme, responsive down to phone width.

Usage

1. Open the live demo (or index.html locally).
2. Paste your first list into A and your second into B (one item per line).
3. Toggle ignore case / trim if you want loose matching, then Compare.
4. Read the results — in both, only in A, only in B, duplicates, similarity — and copy or download any of them.

Privacy

Nothing leaves your device. There is no server, no backend, no analytics beacon, and no network request with your data. All comparison happens in JavaScript in your browser, and your lists are stored only in your own browser's localStorage. You can read every line of the code — it's one file.

Run it locally

It's a single, self-contained HTML file — no build step, no npm install, no dependencies:

git clone https://github.com/kktheglider/ListCompare.git
cd ListCompare
# then just open index.html in any browser (or serve the folder)
python -m http.server 8000    # optional: http://localhost:8000

Deploy

Because it's one static file, host it anywhere: GitHub Pages, Vercel, Netlify, Cloudflare Pages, S3, or your own server — just publish index.html. (The live demo runs on Vercel.)

Tech

Vanilla HTML + CSS + JavaScript, no framework and no dependencies (Inter / JetBrains Mono web fonts are the only external assets). ~34 KB, works offline once loaded.

License

MIT — see LICENSE.