List Comparator
Compare two lists and instantly find items that are only in A, only in B, in both, or the combined union. Case-insensitive mode, deduplication, and per-section download included.
List Comparator lets you paste or upload two lists and instantly see what's unique to each, what they share, and their combined union. It works entirely in your browser — no data is ever uploaded to a server.
Tool interface
List A / List B — Paste items (one per line) or click Load File to import from a file. Supported formats: .txt, .csv, .tsv, .md, .log, .html, .json, .xml (max 5 MB each). When you load an Instagram export HTML file (followers_1.html or following.html), usernames are extracted automatically and an Instagram badge appears next to the counter.
Options bar
- Case insensitive — treats
Appleandappleas the same item - Sort A–Z — sorts each result set alphabetically
- Trim whitespace — strips leading/trailing spaces from each item
- Remove duplicates — deduplicates items within each list before comparing
Compare Lists — runs the comparison and shows four result panels:
| Panel | What it contains |
|---|---|
| Only in A (blue) | Items that exist in A but not in B |
| Only in B (green) | Items that exist in B but not in A |
| In both A ∩ B (amber) | Items present in both lists |
| Union A ∪ B (gray) | All unique items across A and B |
Each panel has Copy, Download .txt, and a list-view toggle (☰) button. Switching to list view renders items as individual rows with checkboxes, plus All, None, and Copy Selected controls.
Instagram usage
- Go to Instagram → Settings → Your activity → Download your information
- Request and download your data package
- Locate
followers_1.html(your followers) andfollowing.html(accounts you follow) - Click Load File → select
followers_1.html→ set as List A - Click Load File → select
following.html→ set as List B - Click Compare Lists
Result interpretation:
- Only in A = people who follow you but you don't follow back
- Only in B = people you follow who don't follow you back
- In both = mutual follows
Use the tick-select list view in "Only in B" to handpick accounts to unfollow.
Common use cases
- Instagram audience analysis — find non-reciprocal followers/followings
- Email list deduplication — merge two mailing lists without duplicates
- Keyword research — compare competitor keyword sets to find gaps
- Inventory reconciliation — spot items missing from one list vs another
- Team name matching — find overlapping or missing members across two rosters
FAQ
How large a file can I upload?
Up to 5 MB per file. A typical Instagram export with thousands of followers is well under 1 MB.
Is my data sent to a server?
No. All processing happens locally in your browser using the FileReader API. Nothing leaves your device.
What file types are accepted?
Plain text formats: .txt, .csv, .tsv, .md, .log, .json, .xml, and Instagram's .html export files.
What is "Case insensitive" mode?
When enabled, Alice and alice are treated as the same item. Useful for email addresses or usernames that may differ in capitalisation.
Can I compare more than two lists?
Currently two lists only. For multi-list comparisons, use the Union result as one of the inputs in a new comparison.
Why does the Instagram badge appear?
When the tool detects Instagram profile URLs (e.g. https://www.instagram.com/username) in the loaded HTML file it switches to Instagram mode and extracts only usernames — one per line.