Is this Git diff or Unix diff format?

Visual side-by-side by default — easier to read than unified diff output. Toggle 'unified mode' for the patch-style format Git uses, which you can save to a .diff file.

Can it ignore whitespace changes?

Yes — three modes: case-sensitive everything, ignore trailing whitespace, ignore all whitespace. The third is most aggressive — treats 'a b' and 'a b' as identical. Useful when comparing across editors with different formatters.

Does it handle very large files?

Lines up to a few hundred-K work smoothly. Multi-megabyte files may stall the diff algorithm. For repo-scale comparisons, fall back to Git or a desktop tool like Beyond Compare.

Is my data sent anywhere?

No — the diff runs entirely in your browser.

LCS · line-level · side-by-side · local

Compare two texts side by side

Spot every addition, deletion, and unchanged line. Built on the classic LCS algorithm — fast, deterministic, and entirely local.

Diff Checker

Rows

compared

Added

Removed

−

Equal

matched

input · sources (162 B)

OriginalChanged

output · diff (5)

  The quick brown fox

  The quick brown fox

− jumps over the lazy dog.

+ leaps over the sleepy dog.

  Line three is unchanged.

  Line three is unchanged.

+ And a brand new line.

Quick Start

How the diff works

We run the Longest Common Subsequence (LCS) algorithm over the lines of both texts, then walk the resulting DP table to emit equal, added, and removed rows.

01
Paste both versions
Original on the left, changed on the right.
Inputs are treated as UTF-8 throughout the pipeline and validated client-side as you type — nothing dispatches until the value is well-formed.
inpututf-8client-sidevalidated
input · texttwo sides · set
```
A vs B
```
loaded · parsedclient-side
02
Skim the colours
Green is new, red is removed, neutral is unchanged.
Each toggle re-computes through a memoised hook, so flipping options never resets your input and the UI stays snappy on large inputs.
legendoptionslivememoisedtoggles
legend · memoised+−= · live
```
+ added
− removed
```
options set · memoisedlive
03
Check the counts
Header tallies live as you edit.
Randomness — where used — comes from crypto.getRandomValues, never Math.random. Heavy work sits in useMemo.
statscomputeinstantlocaldeterministic
added · instant2 · computed
```
+2 / −1
```
computed · instantinstant
04
Refine the inputs
Tweak whitespace or wording and watch the diff update.
Copy writes through navigator.clipboard and downloads use a Blob — zero network traffic. Same input plus same options always yield the same bytes.
editcopydownloadzero-networkreproducible
ok · copiedready · copied
```
live
```
shipped · ready to shipsuccess

Pro tips

Pro tips for everyday utilities

Reach for crypto.getRandomValues

Cryptographically random for IDs, tokens, salts. Math.random is for animation and games, not security.

Sort IDs lexicographically

UUID v4 has no time ordering. Use ULID or UUID v7 if you need sorted IDs.

Mock data with seeds

Faker-style libraries can be seeded so tests are reproducible. Embed the seed in the fixture file.

Reference cards beat memory

Cheatsheets for Vim, Git, Docker, Linux signals are faster than man pages when you’re mid-flow.

Browser APIs vary

Touch events, gamepads, and clipboard differ across vendors. Feature-detect before use.

Persist in the right place

localStorage for user preferences, sessionStorage for transient state, IndexedDB for structured data.

Use Cases

When to compare text

Reviews, drafts, configs.

Code review

Spot edits in copy-pasted snippets faster than the eye. Random values come from crypto.getRandomValues — cryptographically secure for tokens, salts, and session IDs. Math.random is deterministic enough for animations but predictable enough to be a security bug.

CSPRNG-backed

Draft revisions

Compare two versions of a doc paragraph. Pair with hashids, ULID, or UUID v7 when you need both random and sortable — useful for primary keys, public-facing IDs, and event log ordering without a sequence column.

reproducible

Config audits

Diff two snippets of YAML or env files. Output is deterministic given the same seed, so fixtures and tests stay reproducible across CI runs and contributor machines. Embed the seed in the fixture file for full replay.

snappy

Log triage

Catch the one log line that changed between runs. Heavy work runs through useMemo so the UI stays snappy on large inputs. Same input + same options yields identical bytes — the kind of stability snapshot tests rely on.

feature-detected

Migration QA

Confirm what's different between API responses. Storage tools persist to the right backend: localStorage for user preferences, sessionStorage for transient state, IndexedDB for structured data. Pick the right shelf and quota worries disappear.

deterministic

Localisation diff

See how a translation drifted from the source. Browser feature detection: clipboard, fullscreen, gamepad, and Web Bluetooth APIs gracefully fall back when unavailable. No surprise white screens on Safari or older Firefox.

i18n

FAQ

Frequently asked questions

Is the diff at line, word, or character level?

Line level — the standard for text and source code. For finer granularity, paste smaller chunks.

What's the size limit?

Each side must be 2000 lines or fewer. Beyond that, paste smaller selections.

Does whitespace count?

Yes. Lines differing only in spaces show as add/remove pairs.

Can I export the diff?

Not directly — copy from the panel. Use File Diff for unified-diff output.

Is anything sent to a server?

No. The LCS runs locally in your browser.

Suggest a tool

Something missing?

Tell us what you need. We ship the top requests every two weeks.

47 in queue·8 shipped this month

Request queued. Thanks!