How to use the Text Diff Checker
1. Paste the original text in the "Original Text" field on the left.
2. Paste the modified text in the "Modified Text" field on the right.
3. The diff result appears below in real-time, highlighting added lines in green and removed lines in red.
4. Lines without highlighting are unchanged (equal in both versions).
What is it?
A text diff (short for "difference") compares two versions of text and shows what changed. It uses the Longest Common Subsequence (LCS) algorithm — the same core algorithm used by Git's diff engine.
Diff tools are essential for code reviews, document tracking, configuration management, and debugging. When you run git diff in a terminal, it uses a similar algorithm to show what lines were added (+) or removed (-) between commits.
This tool performs line-by-line comparison. Lines shown in green were added in the modified text; red lines were in the original but removed. Unchanged lines appear without highlighting. This is a unified-style diff view, the most common format used in version control systems.
Example
Original: "The quick brown fox jumps over the lazy dog." Modified: "The quick brown fox leaps over the lazy cat."
- The quick brown fox jumps over the lazy dog. + The quick brown fox leaps over the lazy cat.
Lines in red were removed; lines in green were added. Unchanged lines appear without highlighting.
Benefits
See exactly what changed between two versions
Additions and deletions are highlighted line by line — changes are impossible to miss, even in long documents.
Compare API response snapshots before and after a code change
Confirm your refactor didn't silently change the response structure or any field values.
Review configuration changes before applying them
Diff your .env, nginx.conf, or Kubernetes YAML before deploying to confirm only the intended changes are present.
Verify copy edits match the original intent
Compare the original and revised text to confirm only intended changes were made — no accidental deletions or additions.
Frequently asked questions
What algorithm does this use?
It uses the Longest Common Subsequence (LCS) algorithm to find the minimum set of changes needed to transform the original text into the modified text. This is the basis of most diff tools including GNU diff and Git.
Can I compare files?
This tool works with pasted text. Paste the contents of both files to compare them. For large files, copy-paste relevant sections.
Why are some lines shown as both removed and added?
When a line is modified (not completely identical), it appears as removed (old version) and added (new version) side by side. Character-level diffing is not implemented in this tool.
Is there a size limit?
There's no hard limit, but very large texts (thousands of lines) may slow down the browser due to the O(n*m) complexity of the LCS algorithm. For large files, consider using a dedicated diff tool or git diff.