A ∩ B · A \ B · B \ A · Excel · CSV

Compare Two Lists

Compare two lists and see what they share and what each one is missing. Paste a list into each box — or copy two columns straight out of Excel or Google Sheets, or load a CSV file — and all five results appear at once: items in both lists, only in List A, only in List B, in exactly one list, and every unique item.

Nothing is uploaded; the comparison runs in your browser. Each list shows its own accounting line — 5 rows → 3 unique · 2 blanks removed — so no row disappears without an explanation, and a Yes/No match column goes straight back into your sheet.

List A

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0 characters pasted

List B

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0 characters pasted

Matching rules

Separator

Result order

Output format

Trim surrounding spaces

Case-insensitive matching

Ignore blank items

Unicode normalize (NFC)

Clean invisible characters

Collapse internal spaces

Ignore leading zeros

Set relationships between your lists

Paste a list into each box to compare them.

List A: 0 characters pasted

List B: 0 characters pasted

Common to both

A ∩ B

0

Every item that appears in List A and in List B.

Nothing compared yet — paste a list into each box.

Only in List A

A \ B

0

In List A, missing from List B.

Nothing compared yet — paste a list into each box.

Only in List B

B \ A

0

In List B, missing from List A.

Nothing compared yet — paste a list into each box.

In exactly one list

A △ B

0

Everything the two lists do not share, from either side.

Nothing compared yet — paste a list into each box.

All unique items

A ∪ B

0

Every distinct item across both lists, counted once.

Nothing compared yet — paste a list into each box.

Occurrence counts

Set operations answer which items; this table answers how many times. Useful when a duplicate is the bug you are hunting.

No items yet.

Row-by-row match column for Excel

Yes or No for every row of a list, in its original order, answering “is this item in the other list?” Duplicates keep their own row and blank rows stay blank, so the column lines up with your sheet: paste it into the empty column beside the data. It does the job of a COUNTIF helper column.

Rows of List A → In List B? Yes / No
Rows of List B → In List A? Yes / No

TSV · CSV · UTF-8 · UTF-16

Compare two lists from Excel or CSV

Copy the columns. Select two columns in Excel or Google Sheets, header row included or not, and paste them into List A. Spreadsheets copy cells as tab-separated rows, so the box reads a table and compares column 1. Press Put column 2 in List B and the second column becomes List B, row for row. Pasting each column into its own box works too.
Check the header row. The box names the row it leaves out. For pasted cells it assumes a header only when the column underneath holds numbers, codes with digits or email addresses, because calling a real first item a header would lose it; in a .csv or .tsv file an all-text first row counts. Tick or untick First row is a header to overrule it.
Or load a file. Comma, semicolon and tab separators are recognised, quoted fields keep their commas and line breaks, and UTF-8, UTF-16 (Excel's "Unicode Text") and older Windows-1252 CSV files decode. Pick a column, or Whole row to compare complete records.
Take the result back. Plain lines paste one item per row; Tab-separated with counts pastes into three columns; the match column pastes beside your data. CSV downloads carry a UTF-8 byte order mark, which Microsoft documents as the way a UTF-8 CSV opens normally in Excel. In CSV and tab-separated exports, an item that starts like a formula (=, +, - or @) and is not a plain number gets a leading apostrophe, so it opens as text instead of running.

Worked example: customers against unsubscribes

The cells behind Load Excel example. Column B is shorter, and B3 ends in a space Excel does not show:

Example sheet with a Customers column and an Unsubscribed column
Row	A	B
1	Customers	Unsubscribed
2	ann@example.com	BOB@example.com
3	bob@example.com	eve@example.com␣ (trailing space)
4	cara@example.com	ann@example.com
5	dan@example.com
6	eve@example.com

After Put column 2 in List B, with the default rules:

List A: 5 rows → 5 unique
List B: 5 rows → 3 unique · 2 blanks removed
Common to both (3): ann@example.com, bob@example.com, eve@example.com
Only in List A (2): cara@example.com, dan@example.com
Only in List B (0): none: List B is a subset of List A
Match column, List A: In List B? · Yes · Yes · No · No · Yes

The Excel helper column =COUNTIF($B$2:$B$6,A2)>0 filled down from C2 agrees on four rows and gets row 6 wrong: it returns FALSE for eve@example.com because B3 carries a trailing space, which Microsoft warns breaks COUNTIF text matches. The tool trims by default, so eve is correctly marked as unsubscribed. BOB in capitals matches in both: COUNTIF criteria are not case-sensitive either.

Spreadsheet quirks and what happens to them here

Spaces you cannot see: Leading and trailing spaces are trimmed by default, and non-breaking spaces copied from web pages become ordinary ones — Excel's TRIM function, by itself, does not remove those, Microsoft notes.
Capital letters: Matching ignores case by default, as COUNTIF and MATCH do. Switch Case-insensitive matching off when case carries meaning, as in some product codes.
Numbers stored as text: In Excel, MATCH fails when one cell holds the number 123 and the other the text "123". Copied cells arrive as text, so here they match. Display format still matters: Excel copies a cell as the text it shows, so 1,234 and 1234, or 5 and 5.00, differ. Give both columns the same number format before copying.
Leading zeros: 02134 kept as text in one sheet and 2134 as a number in the other match once Ignore leading zeros is on. Going back, Excel strips leading zeros from anything pasted into a General cell: format the target column as Text first (Ctrl+1, Number, Text), or set the column to Text when importing a CSV through Data > From Text/CSV. Past 15 significant digits Excel rounds to zero, which cannot be undone.

COUNTIF · MATCH · XLOOKUP · FILTER

How to compare two lists in Excel

With List A in A2:A6 and List B in B2:B6 — the example above — these are the standard ways to do it inside Excel. Each answers one direction at a time; swap the ranges for the other.

COUNTIF helper column — every Excel version
=COUNTIF($B$2:$B$6,A2)>0
TRUE when the item in A2 is also in List B. Fill down, then filter on FALSE for "only in List A". Ignores case. Reads ? and * in your data as wildcards, returns incorrect results for text longer than 255 characters, and misses matches that differ by a leading or trailing space.
MATCH with ISERROR — Microsoft's own method
=IF(ISERROR(MATCH(A2,$B$2:$B$6,0)),"",A2)
Shows the item when it is in both lists and leaves the cell empty when it is not. MATCH ignores case, and returns #N/A for hidden spaces or for a number compared with the same number stored as text.
XLOOKUP — Microsoft 365 and Excel 2021 or later
=XLOOKUP(A2,$B$2:$B$6,$B$2:$B$6,"Only in A")
Returns the matching item, or "Only in A" through the if_not_found argument. Not available in Excel 2016 or 2019.
FILTER — the whole difference in one formula
=FILTER(A2:A6,COUNTIF(B2:B6,A2:A6)=0,"None")
Spills every item of List A that List B lacks. Microsoft 365 and Excel 2021 or later. It inherits COUNTIF's matching, so on the example it lists eve@example.com alongside cara and dan.
Conditional formatting — highlight, don't extract
Select both columns, then Home > Conditional Formatting > Highlight Cells Rules > Duplicate Values. The rule colours any value that appears more than once in the selection, so a value repeated inside one column lights up even when the other column does not contain it, and nothing is listed for you to copy.

Version availability and pitfalls per the Microsoft Support pages listed under Authoritative sources.
Method	Excel versions	What you get	Trailing spaces
COUNTIF column	All	TRUE/FALSE per row, one direction	Break the match
MATCH + ISERROR	All	Matches shown per row, one direction	Break the match
XLOOKUP / FILTER	365, 2021 and later	Per-row label, or one spilled difference	Break the match
Duplicate Values rule	All	Highlighting only	Break the match
This tool	Any browser	All five results plus a match column, both directions	Trimmed by default

Stay in Excel when the comparison has to update itself as the data changes, or when the answer must sit next to other columns of the same record — formulas do both. Use this tool for a one-off check, for exports from two different systems, for data with stray spaces or invisible characters, or when your Excel lacks XLOOKUP and FILTER.

A ∩ B · A \ B · B \ A · A △ B · A ∪ B

How comparing two lists works

Comparing two lists means computing set relationships between them: the intersection (items in both), the two differences (items only in the first, items only in the second), the symmetric difference (items in exactly one) and the union (every distinct item). A set, in the NIST definition, is "an unordered collection of values where each value occurs at most once" — which is why duplicates inside a single list collapse before any comparison happens, and why this tool prints how many collapsed instead of letting rows vanish.

Read. A table contributes one line per row from the chosen column, header excluded; a plain list is cut on CRLF, lone CR and LF, plus whichever separator you pick.
Normalize. In order: invisible-character cleanup, trim, optional whitespace collapse, Unicode NFC, case fold, blank removal, optional leading-zero strip. The first-seen original text is kept for display, so no panel shows the folded key.
Operate. Membership is a hash lookup, so each item is tested once against the other list's index — O(n + m) rather than the O(n × m) of checking every item against every other.
Report. Lines read, unique items and duplicates collapsed per list, the size of every panel, and a verdict: identical, subset, overlapping or disjoint.

A four-item example you can reproduce

Press Load example: List A is apple, banana, cherry, Banana and List B is banana, cherry, date. List A reports 4 lines → 3 unique because Banana folded onto banana. The panels read: A ∩ B = banana, cherry (2); A \ B = apple (1); B \ A = date (1); A △ B = apple, date (2); A ∪ B = apple, banana, cherry, date (4). Switch case-insensitive matching off and four numbers move at once: List A becomes 4 lines → 4 unique, A \ B grows to apple and Banana (2), A △ B becomes 3 and A ∪ B becomes 5. The intersection holds at 2, because banana and cherry already matched exactly.

Why it stays fast on huge lists

Measured on this implementation, two 100,000-line lists compare in roughly 0.15 seconds and two 500,000-line lists — about 17 MB of text — in around one second. What actually breaks a browser is rendering, not arithmetic, so each panel renders its first 1,000 rows and hands you the rest through Copy and Download, and anything past 50,000 items is computed in a Web Worker so the page keeps responding. Results are built by walking each source list in its own order rather than with the native Set intersection, which returns items in the order of the smaller list and would silently reorder your output.

Common mistakes when comparing two lists

A carriage return you cannot see. A list pasted from a Windows file splits into "apple\r" if a tool only cuts on \n, and then matches nothing. All three newline forms split items here.
Duplicates disappearing without a word. Set semantics collapse repeats by definition, so 1,842 pasted lines can produce 1,790 results. Read the accounting line under each box; for the repeats themselves, open the occurrence table or use the match column.
Composed versus decomposed accents. The word café can be one code point (U+00E9) or two (U+0065 U+0301); rendered they are identical, compared raw they differ. Unicode Standard Annex #15 requires normalizing before comparing, so NFC is on by default — switch it off only when you need byte fidelity for identifiers.
Locale-dependent lowercasing. Under Turkish case rules capital I lowercases to dotless ı, so a locale-aware fold makes the same two lists compare differently on different machines. Case-insensitive matching here uses the locale-independent fold on purpose.
Email case assumptions. The local part of an address may be case-sensitive by RFC, but mail providers in practice treat John@Example.com and john@example.com as one mailbox. Case-sensitive matching on an email list can let an unsubscribed address through.
Mixed separators. Comma-separated text in List A against one-per-line text in List B produces a single long item on one side. The counts under each box expose it immediately, and the box offers the separator it detected. For machine use, the JSON array format drops into a script as-is — tidy it with the JSON formatter — and the quoted, comma-separated format is the shape a SQL IN (…) clause wants, which the SQL formatter lays out once the query grows.

Questions about comparing two lists

Does the tool remove duplicates inside a single list?

Yes. Comparison uses set semantics, where each value occurs at most once, so repeats inside one list collapse before the comparison runs, and the line under each box says how many did. Paste into List A alone and the "Only in List A" panel is your deduplicated list. If you need the repeats themselves, the occurrence counts table and the row-by-row match column keep every row.

Why do two identical-looking items show up as different?

Almost always an invisible character: a trailing carriage return from a Windows paste, a non-breaking space copied out of a web page, a zero-width space from rich text, or an accented letter stored decomposed (NFD) rather than composed (NFC). Keep trim, invisible-character cleanup and Unicode normalization on; the line under each box reports how many characters the cleanup touched.

Are my lists uploaded to a server?

No. Reading files, splitting, normalization and every set operation run in your browser, on the main thread for small lists and in a Web Worker for large ones. No list content is transmitted, logged or stored. You can confirm it by opening your browser devtools Network tab while you compare two lists.

How large a list can I compare?

The enforced ceiling is 20 million characters across both boxes, roughly 20 MB of text, and 20 MB per uploaded file. Past 50,000 parsed items the comparison moves into a Web Worker so the page keeps responding, and each panel renders its first 1,000 rows with the full result available through Copy and Download. Two 100,000-line lists compare in roughly 0.15 seconds and two 500,000-line lists in about one second.

My list is comma-separated, not one item per line. Will it work?

Yes. Choose comma, semicolon, tab, pipe, any whitespace or a custom separator. Line breaks always separate items as well. When a list arrives as a single line, the box offers the separator it detected, and the counts under each box show at once whether the split did what you expected.

Can I compare more than two lists?

Compare two at a time and chain the result. Run A against B, press "Send to A" on the panel you care about, then paste list C into List B. Intersection and union are associative, so (A ∩ B) ∩ C equals A ∩ B ∩ C, and the same trick narrows a suppression list across any number of sources.

How is this different from a text diff tool?

A diff is order-sensitive: it walks two documents line by line and reports insertions, deletions and moves in sequence. Comparing two lists ignores order and position and reports membership only. To see what changed between two versions of the same file, use a diff; to know which items are shared, missing or extra, compare the lists.

Authoritative sources

Microsoft Support - COUNTIF function
States that criteria are not case sensitive, that ? and * act as wildcards, that strings longer than 255 characters return incorrect results, and that leading or trailing spaces break text matches.
Microsoft Support - MATCH function
MATCH does not distinguish upper from lower case, and returns #N/A when no match is found.
Microsoft Support - How to compare data in two columns to find duplicates in Excel
The IF(ISERROR(MATCH(...))) helper column quoted in the Excel section.
Microsoft Support - How to correct a #N/A error in INDEX/MATCH functions
Lists hidden spaces and numbers formatted as Text as causes of a failed match.
Microsoft Support - XLOOKUP function
Syntax, the if_not_found argument, exact match as the default, and that XLOOKUP is not available in Excel 2016 and Excel 2019.
Microsoft Support - FILTER function
Available in Microsoft 365 and Excel 2021 or later; without if_empty an empty result is a #CALC! error.
Microsoft Support - Filter for unique values or remove duplicate values
The Conditional Formatting > Highlight Cells Rules > Duplicate Values steps.
Microsoft Support - TRIM function
TRIM removes ordinary spaces but, by itself, not the non-breaking space character (decimal 160).
Microsoft Support - Keeping leading zeros and large numbers
Excel strips leading zeros and rounds past 15 digits; format cells as Text before pasting, or set a column to Text when importing a CSV.
Microsoft Support - Opening CSV UTF-8 files correctly in Excel
Excel opens a UTF-8 CSV normally if it was saved with a byte order mark, which is why CSV downloads here carry one.
Microsoft Support - Import or export text (.txt or .csv) files
A comma decimal separator makes Excel save CSV files with semicolons, which is why the file reader detects the separator.
NIST Dictionary of Algorithms and Data Structures - "set"
The formal definition this tool implements: an unordered collection where each value occurs at most once, with intersection, union and difference.
MDN Web Docs - Set.prototype.intersection()
The native intersection returns elements in the order of the smaller operand, which is why this tool re-indexes results against List A instead.
Unicode Consortium - UAX #15, Unicode Normalization Forms
Why canonically equivalent strings (composed and decomposed accents) must be normalized before they can be compared for equality.
Unicode Standard, Core Specification, Chapter 5 - Implementation Guidelines
Section 5.18 on case mapping, including the Turkish dotted and dotless I that a locale-dependent lowercase would apply.

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