Free Text Diff Checker

How this tool computes its result

Compares two text blocks line-by-line using a dynamic-programming longest-common-subsequence (LCS) algorithm. The tool builds an n×m DP table where n and m are the line counts of the two inputs, filling it with suffix match lengths. It then backtracks through this table to classify each line as equal (present in both), added (in version B only), or removed (in version A only). The diff output renders in unified format (lines prefixed with "- ", "+ ", or two spaces for unchanged), and a summary panel tallies counts of added, removed, and unchanged lines across the entire comparison.

Worked example

Pasting "Line 1 Line 2 Line 3" into Version A and "Line 1 Line 2 Modified Line 3" into Version B produces a diff showing Line 1 unchanged, Line 2 marked as removed with original text, Line 2 marked as added with modified text, and Line 3 unchanged. The summary panel reports 1 added, 1 removed, and 2 unchanged lines. Copying the diff output yields a unified format string beginning with " Line 1 - Line 2 + Line 2 Modified Line 3".

When not to use this tool

This is a line-by-line diff only — it has no word-level or character-level granularity, so a line with a single comma difference is reported as fully removed and fully added rather than highlighting just the changed character. It also has no three-way merge capability and no whitespace-normalization options, so trailing space differences register as separate lines.

Common mistakes

• - Pasting code with mixed line endings (some CRLF, some LF) — the split on " " only strips the newline itself, leaving any trailing " " as part of the line, so two logically identical lines with different line-ending styles appear as different and register as a remove + add.
• - Assuming the diff output can be used directly as a patch file — the unified format it produces is human-readable but lacks the file headers and @@ offset markers required by patch tools, so you cannot feed its output to git apply or patch.
• - Expecting whitespace-only changes (adding or removing blank lines) to show up clearly — blank lines register as equal or added/removed, but a view of " " (unchanged spaces) is visually indistinguishable from " " in the unified output.

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