Comparing two versions of a text — whether a document, configuration file, code snippet, or data export — is a task that comes up constantly in software development, writing, and data work. A text diff checker identifies what changed between two texts by highlighting additions, deletions, and unchanged sections.
How diff algorithms work
Most text diff tools use variants of the Longest Common Subsequence (LCS) algorithm, originally described by Myers in 1986 and used by Git to this day. The algorithm finds the longest sequence of lines that appear in both texts in the same order, then marks everything else as added or removed.
Given two texts A and B, lines that appear in the LCS are unchanged. Lines in B that are not in the LCS are additions (marked with +). Lines in A that are not in the LCS are deletions (marked with -). The minimal edit script — the smallest set of additions and deletions that transforms A into B — is what most diff tools display.
Line-based vs. character-based diff
Most general-purpose diff tools operate at the line level: a line either matches or it doesn't. This works well for source code, configuration files, and structured data where a change to one word usually represents a meaningful logical change to the entire line.
For prose documents and natural language text, character-level or word-level diff is more useful. It shows exactly which words changed within a line, which is harder to read in terminal output but more intuitive for document editing. Microsoft Word's Track Changes and Google Docs' version history use word-level comparison.
Practical use cases
Code review. Before merging a pull request, reviewing the diff tells you exactly what code changed, added, or was removed. Most code review platforms (GitHub, GitLab, Bitbucket) display Git diffs in a split-view or unified-view format.
Document editing. When collaborating on a contract, policy document, or article, comparing the original and revised version instantly shows what your collaborator changed without reading both versions in full.
Configuration file auditing. Comparing a production configuration against a known-good baseline or against a staging configuration reveals differences that could explain unexpected behavior or security gaps.
Data validation. Comparing two CSV exports or database dumps from different time periods shows exactly which records were added, modified, or removed.
How to compare two texts using TextUtils
- Go to the Text Diff Checker on TextUtils.
- Paste the original text in the left panel.
- Paste the modified text in the right panel.
- Click Compare to see the highlighted diff output: green lines were added, red lines were removed, grey lines are unchanged.
Command-line diff for developers
On Unix-like systems, the diff command compares two files: diff original.txt modified.txt. Use diff -u for unified diff format (the standard format used by Git patches) or diff -y for side-by-side comparison. git diff compares working tree changes against the last commit, and git diff HEAD~1 compares against the previous commit.