Compare Lists — Differences, Overlap and Duplicates
Paste two lists, get five answers at once: only in A, only in B, in both, everything deduplicated, and everything they disagree about. The clean-up options run before any comparison happens, which is the part that decides whether the answer is useful — "Apple " and "apple" are the same row in every real export and different strings in every naive diff. Every panel copies, sorts and exports on its own.
Private by design. Both lists are split and compared in your browser — the data is never uploaded, and closing the tab is all it takes to erase it.
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How to compare two lists
- Paste both lists. One item per line in each panel. A .txt or .csv file can be loaded straight in instead, and comma-separated data can be split into lines with the CSV toggle.
- Set the clean-up rules. Trim spaces is on by default because trailing whitespace is the single most common cause of a false difference. Turn case sensitivity on only if the data genuinely distinguishes case — email addresses and SKUs usually do not.
- Strip the noise with find-and-replace. If one list carries a prefix the other does not — "SKU-" on one export, bare numbers on the other — replace it away before comparing rather than editing both lists by hand.
- Read the five panels. Only in A is what you lost, only in B is what appeared, in both is the overlap, and the counts at the top tell you how many duplicates each list had before deduplication.
Frequently Asked Questions
- How do I find what two lists have in common?
- Paste them into A and B and read the "In both" panel — it is the intersection, shown in A's order. The header strip also gives the overlap as a percentage of A, which is usually the number you actually wanted when the lists are different lengths.
- Why do identical-looking items show as different?
- Almost always invisible whitespace or case. Trailing spaces survive every copy out of a spreadsheet, and "Smith" and "smith" are different strings. Trim is on by default and case sensitivity is off by default for exactly that reason — if two items still differ, check for a non-breaking space or a smart quote.
- Does it remove duplicates?
- Every result panel is deduplicated, and the header shows how many duplicates each input had. First occurrence wins, so the surviving row keeps the position it had in your original list rather than being re-sorted.
- Can I compare columns from Excel?
- Copy the column and paste it — a copied spreadsheet column arrives as one item per line already. If your data is a comma-separated row instead, turn on "Split on commas" and each value becomes its own entry.
- Is my data uploaded anywhere?
- No. Both lists are split and compared by JavaScript running in this page. There is no request carrying your data, nothing is stored, and closing the tab is all it takes to erase it — which matters when the lists are customer emails or unreleased SKUs.
- What is the difference between "Differences" and "Only in A"?
- "Only in A" is one side. "Differences" is the symmetric difference — everything in exactly one of the two lists, both directions at once. Use the first when you are auditing a single list against a reference, the second when neither list is authoritative.
Use Cases
- Find which emails from an old export are missing from the new one
- Diff two SKU or inventory lists after a system migration
- Check a keyword list against the ones you already rank for
- Deduplicate a pasted column and count how many duplicates it had
- Reconcile two attendee or member lists from different sources
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