Text Diff Tool

About This Tool

Compare two text documents and highlight differences.

What Is a Text Diff?

A text diff is a side-by-side comparison of two blocks of text that highlights exactly what changed between them. Additions are shown in green, deletions in red, and unchanged sections stay neutral — so you can see at a glance what was added, removed, or modified without reading both versions line by line.

Diffing is one of the oldest and most useful tools in computing. It powers version control systems like Git, code review tools like GitHub and Bitbucket, document comparison features in Google Docs and Microsoft Word, and file sync utilities like rsync and Dropbox. Whenever two versions of something need to be reconciled, a diff algorithm is doing the work behind the scenes.

How Diff Algorithms Work

At its core, a diff algorithm solves the longest common subsequence (LCS) problem: given two sequences, what's the longest chain of items that appears in the same order in both? Anything outside that chain is either an addition or a deletion.

The most widely used diff algorithm — the one Git uses — is called Myers' diff algorithm, published by Eugene Myers in 1986. It runs in O(ND) time, where N is the total length of both inputs and D is the number of differences. When two versions are similar, D is small and the algorithm runs very fast.

Modern tools add refinements on top of Myers' algorithm, including:

• Line-level diffing — splitting text into lines first, then computing the diff between line sequences. This is what Git shows you in a pull request.
• Word-level diffing — comparing individual words rather than lines. Useful for prose where one word changed inside an otherwise identical sentence.
• Character-level diffing — the finest granularity. Great for spotting typos or subtle changes in short strings.
• Semantic diffing — used by some code editors to understand that reformatting, renaming variables, or moving a block of code isn't a "real" change.

When to Use a Text Diff Tool

• Code review — compare a file before and after editing to see exactly what changed.
• Contract and legal documents — spot edits between two versions of an agreement without reading the entire document.
• Writing and editing — compare drafts to see what your editor changed.
• Configuration comparison — check whether aconfig.json or .env file changed between environments.
• Data validation — verify that two exports or database dumps match (or find where they don't).
• Translation work — compare translated strings against the original source.
• Debugging — compare logs from two runs to isolate what changed.

Understanding the Diff Output

Most diff tools use a standard set of symbols and colors:

• Lines with + (green) — added in the new version. These exist only on the right side.
• Lines with - (red) — removed from the old version. These exist only on the left side.
• Lines with a space or nothing — unchanged. Present in both versions.
• Inline highlights — within a changed line, the exact characters or words that differ are highlighted to show the minimal edit.

Reading a diff is a skill worth developing. Once you get used to the format, you can scan hundreds of lines in seconds and spot the exact changes that matter.

Side-by-Side vs Inline Diff

There are two common layouts for displaying diffs:

• Side-by-side — original on the left, modified on the right, aligned so corresponding lines sit next to each other. Best for long documents and code, where you want to see context.
• Inline (unified) — both versions interleaved into a single column, with additions and deletions marked. More compact; standard in Git and code review tools.

Our tool supports both layouts — switch between them based on the task. Side-by-side is easier for prose and legal docs; inline is easier for code where you want to see the change in flow.

Character, Word, and Line Granularity

Choosing the right granularity changes what the diff highlights:

• Character — pinpoints single-character typos and whitespace differences. Best for short strings or critical precision.
• Word — highlights words that changed inside otherwise identical sentences. Ideal for prose editing.
• Line — treats each line as a unit. Best for code, configuration files, and structured data.

Why Privacy Matters for Diff Tools

The text you compare in a diff tool often contains sensitive information — legal contracts, code with API keys, private notes, customer data, or configuration secrets. Uploading it to a remote server for comparison is a real privacy risk. Our Text Diff Tool runs entirely in your browser using native JavaScript. Your text never leaves your device, never touches our servers, and is never logged. You can verify this by opening your browser's Developer Tools → Network tab — no requests are made when you paste or compare text.

Common Diff Options Explained

• Ignore case — treats "Hello" and "hello" as identical. Useful for email drafts and informal writing.
• Ignore whitespace — collapses runs of spaces, tabs, and newlines before comparing. Essential when comparing code that was reformatted by a different editor.
• Ignore blank lines — skips lines that contain only whitespace. Helpful when comparing documents with different spacing conventions.
• Highlight inline changes — shows the exact characters or words that changed inside a modified line, not just the whole line.