Text Diff

About this tool

Text Diff compares two versions of a text line by line and highlights the lines that differ, side by side, right in your browser. Paste the original on the left and the revised version on the right, click Compare, and changed lines are marked in each column with line numbers, along with counts of compared, changed, and unchanged lines. Spotting a single changed word buried in three paragraphs by eye is error-prone and slow; a line-aligned view makes edits obvious. Lines are aligned with a longest-common-subsequence diff, so inserting or deleting one line marks only that line instead of shifting everything after it, while reworded lines show the old and new versions side by side. Useful for comparing contract revisions, editing drafts, auditing copy changes, or checking that a find-and-replace touched only the intended lines. Nothing is uploaded.

Why use it

• Side-by-Side Comparison: View original and modified text simultaneously so context is never lost while reviewing changes.

• Line-Level Changes Highlighted: Every changed line is pinpointed so you never miss an edit buried in a long document.

• Added & Removed Lines Color-Coded: Green for additions, red for deletions — the same visual convention as GitHub code review.

• No File Upload Required: Paste text directly — no need to save files or navigate upload dialogs.

• Instant In-Browser Processing: The diff runs client-side when you click Compare or Swap, with no upload or server round-trip.

• Privacy-First Design: Your document contents never leave your device — ideal for confidential contracts or drafts.

How to use

1. Paste the original version of your text into the left panel labeled 'Original'.
2. Paste the revised version into the right panel labeled 'Modified'.
3. Click Compare; the diff result appears below, color-coded by change type.
4. Green lines are additions present only in the revised version.
5. Red lines are deletions present only in the original version.
6. Unchanged lines appear without color to provide context around each edit.

When it helps

• When reviewing edits made to a contract, policy, or legal document.
• When comparing two drafts of a blog post to see what an editor changed.
• When verifying that a find-and-replace operation modified only the intended lines.
• When auditing copy changes between a content brief and the delivered article.
• When comparing two exported configuration files or environment variable lists.
• When proofreading translations by diffing the source against a back-translation.

Examples

Tips

• Normalize both texts to the same case using Case Converter before diffing if you only care about content changes, not capitalization.
• Use the diff tool after running Find & Replace to confirm only your intended substitutions were made.
• For long documents, copy just the changed section into both panels to get a focused, faster-to-read diff.
• Paste JSON into both panels after making edits — the line diff will immediately show which keys or values changed.
• When collaborating over email, paste the 'before' version into the left panel and the received 'after' version into the right to audit all changes.

Frequently Asked Questions

Glossary

Diff

Short for 'difference'. A diff is the computed set of changes between two versions of a text, listing added, removed, and unchanged lines.

Hunk

A contiguous block of changed lines in a diff output, typically surrounded by a few unchanged context lines.

Context Lines

Unchanged lines shown around a change in a diff to help the reader understand where in the document the change occurred.

LCS (Longest Common Subsequence)

The algorithm underlying most text diff tools. It finds the longest sequence of lines shared between both versions to determine what changed.

Insertion

A line present in the modified text but absent from the original — shown in green in a diff view.

Deletion

A line present in the original text but absent from the modified version — shown in red in a diff view.