Text Diff Checker

The Text Diff Checker compares two blocks of text and shows you exactly what changed between them, line by line. Added lines, removed lines and unchanged lines are clearly marked so you can spot every edit at a glance, instead of reading both versions side by side and trying to find the differences with your eyes.

It is built for writers comparing draft revisions, developers reviewing changes to code or configuration, editors checking what a collaborator altered, and anyone who needs to confirm whether two documents are truly identical. The comparison uses a longest-common-subsequence algorithm, the same technique behind professional diff tools, so the result lines up matching content intelligently rather than naively comparing line numbers.

Everything runs locally in your web browser using JavaScript, with no upload and no server processing. Paste the original text on one side and the new version on the other, and the differences appear instantly. Because nothing is transmitted, even confidential contracts, private drafts and proprietary code can be compared with complete privacy on your own device.

Features

• Compares two texts line by line and marks each line as added, removed or unchanged using clear prefixes.
• Uses a longest-common-subsequence algorithm to align matching lines intelligently, the same approach as real diff tools.
• Counts added, removed and unchanged lines so you can immediately gauge the size and nature of the changes.
• Offers an ignore-case option so differences caused only by capitalisation are treated as matches when you choose.
• Includes a trim-lines option that ignores leading and trailing whitespace so indentation changes do not add noise.
• Clearly confirms when two texts are completely identical so you do not have to scan a long, empty result by hand.
• Lets you upload plain text files into either side so you can compare two saved versions without copying and pasting.
• Runs entirely offline in your browser with no sign-up, no upload and no size limit, keeping both documents private.

How to use Text Diff Checker

1. Paste your original or first version of the text into the left input box, labelled as the first text.
2. Paste the new or second version of the text into the right input box, labelled as the second text.
3. Optionally enable ignore case or trim lines if you want to overlook capitalisation or indentation-only differences.
4. Run the comparison and read the result, where lines starting with a minus were removed and lines with a plus were added.
5. Check the added, removed and unchanged counts to understand how extensive the differences between the versions are.
6. Copy the diff result or download it as a text file when you want to share or record exactly what changed.

Benefits

• Writers compare two drafts of an article or chapter to see precisely what an edit pass added, removed or kept.
• Developers review changes between two versions of a code snippet or configuration file before applying them.
• Editors confirm what a collaborator altered in a shared document without trusting a vague summary of the changes.
• Legal and compliance staff compare two versions of a contract or policy to spot every modified clause quickly.
• Support engineers diff a working configuration against a broken one to find the single line causing a problem.
• Anyone handling sensitive material benefits because both texts are compared locally and never uploaded anywhere.

Line-based diffing is ideal for text where each line is a meaningful unit, such as code, lists, configuration files and prose split into short lines. The tool aligns the longest run of matching lines first, then marks the surrounding lines as additions or deletions, which mirrors how version-control systems present changes and makes the output familiar to anyone who has reviewed a pull request.

The ignore-case and trim-lines options help you focus on substantive changes. If you only care about wording and not capitalisation, ignore case so a capitalised heading does not register as a difference. If indentation or trailing spaces are irrelevant, trim lines so reformatting does not flood the result with false changes, leaving only the edits that actually matter.

All comparison happens locally in your browser, so neither text is uploaded, logged or stored, making the tool safe for confidential documents and private code. The diff works at the line level rather than highlighting individual changed words within a line, so a small edit to a long line is shown as that whole line being removed and a new one added, which keeps the output clear and predictable.