Text Compare Online

A text diff checker compares an original and a modified text line by line. It marks exact matches as unchanged and identifies lines treated as removed or added. The results can be viewed in a unified sequence or paired in a split layout with line numbers.

The comparison uses a longest common subsequence, or LCS, algorithm. It is exact and case-sensitive: spaces, capitalization, punctuation, and hidden carriage-return characters can make two lines different. It does not highlight changed words inside a line.

A line diff is useful when reviewing drafts, configuration, code snippets, lists, or generated output. It makes insertions and deletions visible without requiring a source-control repository.

• Compare an edited document with its earlier version.
• Check generated text or configuration for unexpected line changes.
• Review additions and removals with old and new line numbers.
• Copy a readable patch-like representation for discussion.

Each input is split at line-feed characters. The algorithm builds a dynamic-programming table to find a longest sequence of lines shared in the same order. Shared lines become unchanged entries. When alternatives tie, the implementation chooses a removal before an addition, so repeated identical lines can produce another valid alignment than a different diff program.

Split view groups consecutive removed lines and then consecutive added lines, pairing them by position. That pairing is visual convenience; it does not mean the tool proved that one specific removed line was edited into the line beside it.

Added and removed statistics count lines, not characters or editing operations. A one-character change causes the full old line to be removed and the full new line to be added. Empty input is represented internally by one empty split line, so edge-case statistics can differ from an intuitive “zero lines” model.

The copied output resembles a Git patch with file headers and line prefixes. Its hunk header is a custom summary, and it includes the full comparison rather than standard hunk ranges. Do not assume `git apply` or another patch parser will accept it.

Comparison reduces the risk of overlooking a small but meaningful revision. Exact line matching is especially helpful for structured material, but human review is still needed to understand whether a change is correct, equivalent, or safe.

For m original lines and n modified lines, the LCS table contains roughly (m + 1) × (n + 1) numeric cells. Time and memory therefore grow with the product of the line counts, which can become expensive for very large inputs.

LCS table work and memory ≈ O(m × n)

m

Number of lines in the original input.

n

Number of lines in the modified input.

Use Text Diff Checker for focused, private line comparisons. It provides exact LCS-based results and clear line totals, while deliberately remaining simpler than a word-aware diff or a full source-control patch system.