Text Diff Checker

How to use the text diff checker

1. Paste the first version into Original text and the second version into Changed text. Two short lists are there as a sample.
2. Read the table: a plus sign marks a line that was added, a minus sign marks a line that was removed, and lines with no mark are the same in both. Line numbers for each side are in the first two columns.
3. Tick Ignore upper and lower case or the options for spaces if small differences should not count.
4. Tick Show only the changes to hide long stretches of unchanged lines, then press Copy the diff to copy it as text.

The method

The checker compares whole lines using the longest common subsequence, or LCS. That is the longest list of lines that appear in both texts in the same order, even if other lines sit between them. Every line in the original that is not part of that list is shown as removed, and every line in the changed text that is not part of it is shown as added.

Before the main step, lines that match at the start and at the end of both texts are paired off, which keeps the comparison fast for files with a few edits. The middle is solved with a table of size lines by lines, so very large differences are refused with a clear message instead of freezing your browser. Up to 20,000 lines per side are accepted.

Reading the result

A line you edited appears as a removed line followed by an added line, because the method compares whole lines. A moved paragraph shows as removed in one place and added in another. When two versions have several equally good matches, the removed line is listed before the added line.

The ignore options change only how lines are compared. With case ignored, Hello and hello match. With spaces ignored, extra spaces at the ends and runs of spaces inside a line are treated as one space. The text shown for matching lines is from the changed version. If you only need to see what two lists have in common, the compare two lists tool is faster, and the text cleanup tool can sort or deduplicate lines first.

Good uses and limits

Use it to review edits to a contract draft, check which settings changed between two configuration files, or see what changed between two exports. It works on lines, so it does not highlight which words changed inside a line. For JSON, you can first format both sides in the JSON viewer so every key sits on its own line. Everything runs in your browser and nothing is uploaded.

Assumptions and limits

• A line is any text between line breaks. All common line endings are understood.
• Lines are compared whole. Changes inside a line are not marked word by word.
• The two texts are limited to 20,000 lines each, and the comparison table is limited to 4,000,000 cells.
• Blank lines count as lines and are matched like any other line.

Formulas reviewed October 10, 2026. See the calculation methodology for how SumPanda rounds, tests and sources its formulas.

Frequently asked questions