How are lines compared?

Lines are treated as plain strings and compared byte-for-byte by default. Toggle case-insensitive mode to fold case before comparing.

Are duplicates within a list collapsed?

Yes. Each list is treated as a set, so duplicate lines within the same list don't affect the result.

Where does the comparison happen?

In your browser. Both lists are processed locally without any network call.

union · intersect · difference · symmetric

Merge lists with set operations

Q: What's symmetric difference?

Symmetric difference returns lines that appear in exactly one of the two lists — items present in both are excluded. Useful for finding what changed between two snapshots.

Combine two lists using union, intersection, difference (both directions), or symmetric difference.

Merge Lists Workspace

List A

24 B

List B

28 B

Result

union

Options

a≢A

sorted

list A

list B

result · union

apple
banana
cherry
date
elderberry
fig

Quick Start

How to merge two lists

Five classic set operations. Union for combining, intersection for common items, difference for what's unique to each side.

01
Paste both lists
One item per line in each panel.
Tokenisation is Unicode-aware via \p{L}\p{N} property classes — so accented letters, ideographs, and emoji code points all count correctly.
ABUTF-8Unicodecode points
input · text2 lists · UTF-8
```
A: apple
B: cherry
```
loaded · UTF-8UTF-8 · ready
02
Pick operation
Union (everything once), Intersection (in both), Difference A−B (only in A), B−A (only in B), Symmetric (only in one).
Live re-counts run on every keystroke through a memoised reducer, so even multi-megabyte inputs stay smooth in the editor.
5 opslivememoisedoptionssnappy
op · optionsunion · live
```
apple, banana, cherry
```
options applied · livelive
03
Toggle options
Case-insensitive matching, trim whitespace, sort the result.
Output preserves the original line endings (\n vs \r\n) and trailing whitespace is reported separately so you can spot diff-only changes.
optionsline endingswhitespacediff-cleanreproducible
config · countedset · ready
```
Apple = apple
```
counted · livecounted
04
Copy or download
One click.
Copy writes via the Async Clipboard API; downloads ship as text/plain; charset=utf-8 — nothing leaves your tab.
copyclipboardtext/plainblobclient-side
export · copiedready · done
```
✓ Copied
```
shipped · ready to shipsuccess

Pro tips

Text-processing fundamentals worth knowing

Tokenise with Unicode classes

Use \p{L}\p{N} with the u flag so accents, ideographs, and emoji count properly.

Normalise line endings

Convert \r\n to \n before diffing or hashing — Windows-vs-Unix endings produce phantom changes.

Mind invisible characters

Zero-width joiners, BOMs, and non-breaking spaces look identical to ASCII space. Strip them before comparison or storage.

Stream don’t slurp

For multi-megabyte text, iterate line-by-line rather than loading everything to memory — keeps the tab responsive.

Choose collation deliberately

Default JS sort is code-point order, not human alphabetical. Use Intl.Collator for locale-aware sorting.

Re-run after normalisation

NFC vs NFD changes byte length but not visible glyphs. String.prototype.normalize() before counts and comparisons.

Use Cases

When to merge lists

Anywhere two lists need to be combined or compared.

Mailing list dedupe

Union two mailing lists without duplicates. Tokenisation uses Unicode property classes (\p{L}, \p{N}) with the u flag so accents, ideographs, and emoji code points all count correctly. Surrogate-pair-aware counts mean 🚀 weighs 1, not 2.

Unicode-correct

Diff allowlists

Find what's only in the old vs new allowlist. Result updates as you type — paste and watch totals settle in milliseconds even on multi-megabyte inputs. Heavy work runs through a memoised reducer so the editor never janks.

diff-clean

Common subscribers

Intersect two newsletters' subscriber lists. Output normalises line endings to LF for clean diffs across platforms. Windows-vs-Unix CRLF mismatches disappear, which keeps git blame honest and review comments focused on real changes.

instant counts

Schema migration

Find columns only in old schema vs new. Code-point counts are stable across NFC/NFD normalisation. Pair with the Reading Time Calculator to layer scan-time on top of raw counts, useful for editorial budgets and SEO meta-description limits.

platform-aware

Feature flags

Find flags only enabled in one environment. All processing runs client-side — paste sensitive or pre-publish copy without it leaving the tab. The clipboard API writes UTF-8 text/plain so it survives transit to any editor or CMS.

code-point-accurate

Dependency audit

Compare deps in two package.json files. Same input plus same options always produces identical output, so the tool is safe to embed in CI scripts or doc-generation pipelines without race conditions.

lossless

FAQ

Frequently asked questions

What if items repeat within a list?

Duplicates within a list are kept only once (each operation works on sets).

Does order matter?

No — set operations are commutative for union/intersect/symmetric. Order matters for A−B vs B−A.

Case sensitivity?

Default case-sensitive. Toggle case-insensitive for Apple ≡ apple.

What's symmetric difference?

Items in exactly one of the two lists (XOR) — useful for spotting non-overlap.

Is anything sent to a server?

No. All processing runs locally.

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