Text Diff Checker
Paste two blocks of text and instantly see what changed, line by line.
Text diff checker compares two blocks of text and shows exactly what changed between them. Paste the original text on the left and the modified version on the right. The diff output highlights added lines in green and removed lines in red, with plus and minus markers. The header shows a count of added and removed lines. The algorithm uses LCS (longest common subsequence) to find the minimal set of changes. All comparison runs in your browser with no server involved.
Frequently Asked Questions
- How do I compare two texts online?
- Paste the original text in the left box labelled Original and the modified text in the right box labelled Modified. The diff result appears automatically below, showing added lines in green and removed lines in red. No button click is needed. The comparison updates as you type.
- What does a text diff checker do?
- A text diff checker finds the differences between two versions of a text. LCS (longest common subsequence) identifies which lines stayed the same and which changed. Lines not part of the common sequence are classified as added or removed. The output marks unchanged lines with a dot, new lines with a plus, and deleted lines with a minus.
- Can I use this to compare code?
- Yes. The diff checker works on any plain text, including source code. Paste two versions of a function, a configuration file, or an SQL query to see what changed. The comparison is line-by-line, not word-by-word, which matches how most code review tools work.
- What is LCS algorithm in text comparison?
- LCS stands for Longest Common Subsequence. It finds the longest sequence of lines that appear in both texts in the same order. Lines not part of this common sequence are classified as either added or removed. LCS produces a minimal diff: it shows the fewest possible changes needed to transform one text into the other.
- Is there a character limit for text comparison?
- The tool has no hard character limit. LCS has quadratic time complexity, so very large texts take slightly longer. Texts under 500 lines process instantly. Larger texts produce a result within 1-2 seconds.
What is Text Diff Checker?
Text diff checker compares two blocks of text and highlights what changed between them. Paste the original version on the left and the modified version on the right. The output shows added lines in green, removed lines in red, and unchanged lines in grey. The header displays a count of added and removed lines.
The algorithm is LCS, or Longest Common Subsequence. LCS finds the longest sequence of lines shared by both texts in order. Lines outside this common sequence are classified as insertions or deletions. The result is a minimal diff: the fewest changes needed to transform one text into the other.
How does it work?
The algorithm builds a table comparing every line of the original against every line of the modified text. Each cell records the length of the longest common subsequence up to that point. A traceback reconstructs the sequence of equal, added, and removed lines. Each output line is tagged with its type and rendered with colour coding.
The comparison is case-sensitive and whitespace-sensitive. A line with a trailing space differs from the same line without one. The behaviour matches git diff and most code review tools. Indentation changes count as modifications.
When should you use Text Diff Checker?
Use it to review changes before committing to version control. Paste the old and new versions of a configuration file to confirm only the intended lines changed. Use it to compare two versions of a document to identify edits made by a collaborator.
Use it to spot differences between two API responses that should be identical. Use it to check if a copied code snippet matches the original after formatting. Developers use diff tools daily. Having one in a browser tab without installing software is useful for quick checks on any device.
Tips to get the best results
- For code comparison, make sure both versions use the same indentation style. Mixed tabs and spaces will show many false differences that are not real logic changes.
- Clear both inputs before starting a new comparison. Leftover text from a previous comparison affects the output.
- If you see many changes on lines that look identical, check for invisible characters. Copy both texts through a plain text editor to strip hidden formatting before comparing.
- For comparing JSON, run both through the JSON Formatter first to normalise key order and indentation. Then paste the formatted versions here for a clean diff.