Text Diff / Compare

How to Use the Text Diff Tool

1. Paste the original version of your text into the left panel. This can be a paragraph, an email, a translation source, or any prose passage.
2. Paste the edited version into the right panel.
3. Click Compare. The diff view renders below, showing each line that changed with added content highlighted in green and removed content in red.
4. Scan for unchanged lines in gray between the change markers - that is your context, the prose both writers agreed on.
5. Use Swap to see the diff from the opposite direction, which reveals whether an edit was an addition or a reversion.
6. Use Clear to reset both panels before starting a fresh comparison.

What This Tool Does

The diff runs as a line-based comparison with an emphasis on short, human-readable passages: release notes, blog edits, translation reviews, and chat threads. Behind the scenes it uses a longest-common-subsequence computation to align matching lines between the two inputs, then marks everything else as insertions or deletions. Rendering is done by building DOM text nodes rather than innerHTML, which means angle brackets, ampersands, and other HTML-looking characters in your prose are rendered verbatim instead of being parsed as markup. Nothing about the comparison touches the network: there is no fetch, no telemetry beacon carrying the input, and the Compare button triggers a single synchronous function call within the existing page context.

When You Would Reach for It

• Checking what an editor actually changed in the draft of a blog post before you accept their version.
• Verifying that two translators produced linguistically equivalent output by diffing the English back-translations.
• Reviewing terms-of-service changes between vendor contract revisions and flagging inserted clauses to legal.
• Comparing two versions of an AI-generated response to see where a prompt tweak shifted the wording.
• Auditing Slack or Discord messages pasted from two timestamps to see what a message author edited after the fact.
• Confirming that a grammar or tone rewrite did not quietly drop a factual claim from the original paragraph.

Common Pitfalls and Edge Cases

• Line-break-sensitive comparison. The tool compares whole lines. If the editor reflowed paragraphs at a different column width, every line will appear changed even though the words are the same. Paste one paragraph per line, or run both inputs through a line-flattening step first.
• Smart quotes and em-dashes. Pasting from Word, Google Docs, or a CMS often introduces U+2018, U+2019, U+201C, U+201D, or U+2014 where ASCII characters used to be. These look identical on screen but are different bytes, so they appear as changes. An invisible-character detector (also on this site) reveals them.
• Non-breaking spaces. U+00A0 looks like a normal space but is different from U+0020 and will cause a line to diff against an otherwise-matching line.
• Trailing whitespace. Spaces or tabs at the end of a line count as differences. If they are uninteresting, trim them in a text editor or with the Whitespace Remover before diffing.
• Identical inputs with trailing-newline mismatch. Two pastes that differ only by whether they end with a newline will show a one-line change at the bottom.

What "Text Diff" Actually Means

Text diffing has a long lineage that starts with Hunt and McIlroy's 1976 paper describing the algorithm that became Unix diff, followed by Eugene Myers's 1986 paper that introduced the O(ND) edit-script algorithm modern tools use. The underlying math is dynamic programming over a sequence of tokens - lines, words, or characters - searching for the longest common subsequence (LCS) that maximizes the unchanged portion between two inputs. RFC 6902 (JSON Patch) and the unified-diff format used by GNU diff and Git both grew out of this tradition. Word-level and character-level diffs use the same math applied to a finer granularity, which is why editors such as VS Code can show inline red and green within a single changed line.

Comparison to Alternatives

diff -u on the command line remains the reference tool for file-based text comparison. wdiff produces word-level diffs that are friendlier to prose readers than the line-level default. Google Docs, Notion, and Microsoft Word have built-in track-changes views that are far more ergonomic when the author and reviewer are collaborating inside the same document. Diffchecker.com and several other online tools offer side-by-side layouts with inline word-level highlighting. Use this web tool when your inputs are short passages pasted from somewhere else (a chat, an email, a model response) and you want a quick, private, zero-install comparison. For long documents with rich formatting, a Word-class editor with track changes will serve you better; for version-controlled content, Git is the right answer.