The Text Diff Checker is a free online text compare tool that highlights differences between two documents side by side, showing additions in green and deletions in red. Paste your original text on the left and modified text on the right, then hit the Compare button to see changes instantly. This is useful for comparing two versions of text documents, reviewing changes in a configuration file, checking that a translation preserved all the original content, or verifying that a text was copied correctly. You can also compare code — configuration files, scripts, or any plain-text source. The comparison runs at the word level by default (highlighting individual changed words within lines) or at the line level (marking entire changed lines). Switch between inline view (showing both versions in a single column with changes marked) and split view (showing the original on the left and modified on the right). The tool shows a summary of how many lines were added, removed, and unchanged. All processing runs in your browser with no data sent to any server. For related tasks, Find & Replace can find and replace text patterns, Regex Tester can test and debug regular expressions, and Word Counter can count words, characters, and reading time.
A text comparison tool is most useful when you need a reliable record of what changed between two versions, rather than doing a manual side-by-side review. The algorithm behind most free online comparison tools is the Longest Common Subsequence (LCS) algorithm, which finds the longest sequence of lines (or characters) that appear in both documents in the same order, then marks everything outside the LCS as either an addition or a deletion. This is the same approach used by git and most code review platforms. At the word level, word-by-word comparison produces more readable output than character-by-character analysis for prose: if a sentence changes from "The quick brown fox" to "The fast brown fox", word-level output shows "quick" deleted and "fast" added, while character-level output would show multiple granular changes that are harder to read. For legal text documents and contracts, seeing exactly what changed between a draft and a revised version makes contract review much more reliable. For configuration files, a line-level view is often more appropriate because each line is a distinct setting and adding or removing a single property is a meaningful change. For translated documents, comparing the original and translation side by side can help catch accidentally omitted paragraphs or duplicated sections. Writers use it to track edits between drafts before sending for review. Students use it to compare two versions of an essay and confirm all instructor feedback was addressed. Developers use it outside of version control to spot differences between two snippets of generated output or two API responses. Journalists and fact-checkers use it to compare an original source document against a published article. In each case, the goal is the same: make the difference between two versions immediately visible without requiring a manual read-through.