Diff Checker

Q: Why does my whole file show as changed?

Almost always line endings or indentation. A file saved on Windows uses CRLF where one saved on macOS or Linux uses LF, and most tools treat that as every line differing even though the visible content is identical. Re-indentation — spaces to tabs, or a formatter run — does the same. This tool normalises line endings before comparing and then tells you when the two sides used different ones, so you can tell a real rewrite from a byte-level one.

Q: Is my text uploaded anywhere?

No. The comparison runs entirely in your browser and nothing is transmitted or stored. That matters more for a diff tool than most: people paste environment files, connection strings and production configs into these, and many online diff tools do send both sides to a server.

Q: What algorithm does this use?

Myers' shortest-edit-script algorithm, which is what git, GNU diff and most editors use. The practical difference from a naive comparison is that it finds the smallest set of changes: insert a line at the top of a file and Myers reports one insertion, where comparing line 1 to line 1, line 2 to line 2 and so on would report every line as changed because everything shifted.

Q: Can it detect moved blocks?

No, and no standard line diff does. A block moved from the top of a file to the bottom is reported as a deletion in one place and an insertion in the other, because that genuinely is the shortest edit script — recognising it as a move requires a different and much more expensive analysis. Some review tools layer move detection on top; this one reports the honest minimal diff.

Q: How do I compare two JSON files?

For a text-level view, format both with a JSON formatter first so key order and indentation match, then diff them here. But if you want to know whether the data differs rather than the text, use a structural JSON comparison instead — two JSON documents with the same content in a different key order are semantically identical and will produce a large, misleading line diff.

Q: What does 'ignore whitespace' actually ignore?

It collapses runs of spaces and tabs to a single space and trims each line before comparing, so re-indentation and trailing spaces stop registering as changes. The original text is still what gets displayed — only the comparison is loosened. It does not ignore blank lines, since adding or removing one is usually a real edit.

Compare two texts line by line, with character-level highlighting and the invisible differences explained.

Original

Changed

Ignore whitespace Ignore case

Paste text into both boxes to compare them.

#	Original	#	Changed
#		Line

What It Does

This tool compares two blocks of text and shows what changed, using the same shortest-edit-script algorithm git uses — so inserting a line at the top reports one insertion rather than marking every following line as changed. Within a modified line it narrows the highlight to the characters that actually differ. It also names the invisible causes: different line endings, a missing trailing newline, or a change that is nothing but whitespace, all of which produce diffs that look wrong until someone tells you why.

When to Use It

You have two versions of a config file and need to know precisely what differs.
A deploy behaved differently and you want to compare the environment file against the working one.
You are reviewing an edit someone sent back as a pasted block rather than a pull request.
A file shows as entirely changed in git and you suspect line endings rather than content.

Worked Examples

One line inserted at the top

Reported as a single insertion. A naive line-by-line comparison would call every line changed, because everything shifted down by one — this is exactly what the Myers algorithm exists to avoid.

A one-character change

The line is marked changed, and the character-level highlight narrows it to the single digit that differs. Finding that by eye in a long connection string is genuinely hard.

Whitespace-only reindentation

Spaces became a tab. The analysis flags the change as whitespace-only, so you know a wall of red and green is a re-indent rather than a rewrite. Tick 'ignore whitespace' to confirm nothing else moved.

Identical text, different trailing newline

Invisible in any editor, and the cause of countless one-line diffs nobody can see. The analysis names it explicitly rather than leaving you staring at two lines that look the same.

Common Mistakes

Assuming a big diff means a big change. Re-indentation, a line-ending conversion or a formatter run will mark every line as changed while altering nothing meaningful. Check the analysis before reading the diff line by line.
Ignoring line endings. A file saved on Windows uses CRLF and one saved on macOS or Linux uses LF; the content can be byte-for-byte equivalent and still show as entirely different in git or an editor. This tool normalises them and tells you when the two sides differ.
Missing a trailing newline difference. Whether a file ends with a newline is invisible on screen but is a real byte difference, and it makes the last line appear changed for no visible reason.
Diffing minified or single-line files. A line diff on a file that is one enormous line can only tell you the line changed. Format both sides first — then a line diff has something to work with.
Comparing structured data as plain text. Two JSON documents with the same content but different key order are semantically identical and textually very different. Use a structural comparison for those, not a line diff.

Features

Myers shortest-edit-script algorithm

the same approach git uses

Character-level highlighting within modified lines

Side-by-side and unified views

Ignore whitespace and ignore case

Line-ending mismatch detection

Trailing-newline detection

Whitespace-only change detection

Added

removed and modified counts

Swap sides in one click

Runs entirely in your browser

How to Use

1. Paste the original text on the left and the changed text on the right. 2. The comparison runs as you type; use the view selector for side-by-side or unified. 3. Read the analysis first — it explains line-ending and whitespace causes before you start reading lines. 4. Tick 'ignore whitespace' if the analysis says the changes are whitespace only, to see what else moved.

Frequently Asked Questions

Why does my whole file show as changed?

Is my text uploaded anywhere?

What algorithm does this use?

Can it detect moved blocks?

How do I compare two JSON files?

What does 'ignore whitespace' actually ignore?

Embed this Diff Checker

Paste this snippet into your site to embed the tool.

<iframe src="https://webtoolworld.com/embed/diff-checker" style="width:100%;min-height:560px;border:0" loading="lazy" title="Diff Checker"></iframe>
<p style="font-size:12px;margin-top:6px"><a href="https://webtoolworld.com/diff-checker">Diff Checker</a> by WebToolWorld</p>

Everything runs in your browser — neither text is uploaded, logged or stored. Line endings are normalised before comparison, so CRLF and LF versions of the same content compare as identical while the analysis still tells you they differ. Very large or almost entirely dissimilar inputs are reported as a wholesale replacement rather than a minimal diff, since computing the shortest edit script between unrelated texts costs time without telling you anything useful.