Is this text diff tool free to use?

Yes, completely free. No account, no signup, and no payment required.

Is my text sent to a server?

No. The diff runs entirely in your browser. Your text never leaves your device.

What is the difference between line level and character level diff?

Line level marks entire lines as changed. Word and character level highlight the exact words or characters that changed within modified lines.

What does ignore case mean?

It treats uppercase and lowercase as equal so capitalization changes do not count as differences.

What does ignore extra whitespace do?

It collapses multiple spaces into one before comparing so spacing-only changes are ignored.

Can I compare code files with this tool?

Yes. Paste any plain text including code, JSON, YAML, SQL, or prose.

What algorithm does the diff use?

The Myers difference algorithm, the same one Git and GNU diff use. It finds the smallest set of added and removed lines.

📝 Text Tools ✔ Free Forever

Text Diff Tool Online Free

Paste two versions of any text and see every difference highlighted instantly. Line level and character level diff, side by side or unified view. Runs entirely in your browser.

✔ Line level diff ✔ Character level diff ✔ Side by side view ✔ Unified view ✔ 100% browser-based

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Ignore case Ignore extra whitespace

Original Text (A)

Modified Text (B)

About This Tool

How this text diff tool finds the smallest set of changes between two texts

Comparing two blocks of text for what changed is a matching problem: find the largest set of lines that both texts share, in the same order, and treat everything else as added or removed. This tool solves it with the Myers difference algorithm, the method Eugene Myers published in 1986 and the one Git and GNU diff use by default. It runs on lines first, and then, in word or character mode, again inside each changed line.

The comparison runs entirely in your browser. Neither text is uploaded or logged.

The Myers algorithm, step by step

Myers finds a shortest edit script, the fewest line insertions and deletions that turn text A into text B. Its running time grows with the size of the texts times the number of differences, not with the size of A times the size of B, so two long files that differ in a few places compare almost instantly.

Step 1 Turn lines into ids Every distinct line gets a number, after applying ignore case and ignore whitespace, so the algorithm compares small integers instead of long strings. Windows and Unix line endings are treated the same.

Step 2 Trim the shared start and end Lines that match at the top and bottom of both texts are set aside first, which is often most of a document.

Step 3 Find the middle snake The algorithm searches from both ends at once for the longest run of matching lines in the middle of the remaining block, splits the problem there and repeats on each half. This linear space version keeps memory small even for files with hundreds of thousands of lines.

Step 4 Go inside changed lines A removed line and the added line that replaces it are paired up. In word mode the same algorithm runs on their words, in char mode on their characters, where an emoji or an accented letter counts as one character. Only the parts that really changed are highlighted.

// the core loop: extend each diagonal k as far as lines match x = (k == -d || (k != d && v[k-1] < v[k+1])) ? v[k+1] : v[k-1] + 1; y = x - k; while (x < n && y < m && a[x] === b[y]) { x++; y++; } v[k] = x;

A worked diff

Text A: "The quick fox" / "jumps over the dog" Text B: "The quick fox" / "leaps over the dog"

The quick fox - jumps over the dog + leaps over the dog

The first line matches exactly and is marked equal. The second line differs by one word, so at the line level it is a full removal plus a full addition. Switch to word level and the tool compares the words inside that pair of lines, so only jumps and leaps are highlighted rather than the entire line.

Setting	Effect
Ignore case	Both texts are lowercased before comparison, though the original casing still displays in the output
Ignore whitespace	Runs of spaces and tabs collapse to one space and the line is trimmed before comparison
Unified view	One column, additions and removals shown inline in original document order
Side by side view	Two columns, with blank filler rows keeping both panes aligned

Built for big inputs. Two 50,000 line files with a few hundred edits compare in well under a second. When the result is very long, unchanged stretches are folded to three lines of context around each change, and you can unfold any of them. If two huge texts have almost nothing in common, the tool stops searching after a few seconds and shows the remaining region as replaced instead of freezing your browser.

What gets counted and shown

Stats row

Added, removed and unchanged line counts are shown above the result. The tool also tells you when the texts are identical, when they only differ in ignored case or spacing, and when their line endings differ.

Copy or download as a patch

Copy diff and Download .diff produce a standard unified diff, with @@ hunk headers and three lines of context, the same format as diff -u and Git. It pastes cleanly into a code review comment or ticket and can be applied with patch.

Line level Myers diff Word and character highlights Unified and side by side views Case and whitespace ignoring

Longest common subsequence problem for the matching problem every line diff solves.
Diff for the history of the Unix utility and its output conventions.
Eugene Myers, An O(ND) Difference Algorithm and Its Variations, 1986 for the algorithm this tool and most production diff tools use.
Wagner-Fischer algorithm for the closely related edit distance DP formulation.

Comparisons this makes easy

Comparing two drafts of a contract to spot exactly which clauses changed, reviewing an edited blog post against the original before publishing, checking two versions of a config file line by line, catching what an editor changed in a manuscript, and verifying that a translated document still matches the structure of its source. Word level is the one to reach for when a single word swap inside a long paragraph is what you need to see, and char level for typos and code.

Common Questions

FAQ: Text Diff Tool Online Free

Yes, completely free. No account, no signup, and no payment ever required.

No. The diff algorithm runs entirely in your browser using JavaScript. Your text never leaves your device. Safe to use with confidential documents, contracts, or code.

Line level diff treats each line as one unit and marks entire lines as added or removed. Word level and character level go further and highlight the exact words or characters that changed within each modified line. Use them when you need to spot small edits inside long lines.

When ignore case is on, the tool treats uppercase and lowercase letters as equal. A line that changed only in capitalization will show as unchanged. Useful when comparing text that may have been reformatted.

It collapses multiple spaces and tabs into a single space before comparing. Two lines that differ only in spacing will count as identical. Useful when comparing code that was auto-formatted or pasted from different editors.

Yes. Paste any plain text including code, JSON, YAML, SQL, HTML, or prose. The tool works on any text content.

The tool uses the Myers difference algorithm, the same one Git and GNU diff use by default. It finds the smallest number of line additions and removals that turn one text into the other, and it stays fast on large files.

From the blog