Text Diff Checker
Paste your original and modified texts into the two fields below, then click Compare to see a color-coded diff showing every added, removed, and unchanged line.
How the Text Diff Checker Works
This free online diff checker compares two blocks of text line by line using the Longest Common Subsequence (LCS) algorithm, a well-established technique used in professional tools like Git, diff utilities, and code review platforms. The algorithm identifies the longest sequence of lines that appear in both texts in the same order, then marks any lines not in this common subsequence as either added or removed. The result is a unified diff view with color-coded highlighting that makes changes immediately visible.
Comparison Algorithm
Both texts are split into arrays of lines. The LCS algorithm builds a dynamic-programming matrix to find the longest common subsequence of matching lines. Lines present only in the original are marked as removed (red). Lines present only in the modified text are marked as added (green). Lines that match are displayed as unchanged (muted). Statistics summarize the total lines added, removed, and unchanged.
Why Text Comparison Is Essential
Comparing text versions is a fundamental need across many professions and workflows. Software developers compare code changes before committing to version control systems like Git. Technical writers track revisions across document drafts to ensure accuracy. Legal professionals compare contract versions to identify modified clauses. Editors and proofreaders review text changes made by authors. Translators verify that source documents have not changed between translation rounds.
Without a diff tool, you would need to manually read both versions line by line, which is error-prone and time-consuming. Even small documents can contain subtle changes that are easy to miss with the naked eye, such as a single character change in a URL, a modified date, or a swapped word. This tool highlights every difference automatically, ensuring nothing slips through the review process.
Understanding the Color-Coded Output
The diff output uses three colors to indicate the status of each line. Green lines with a plus prefix represent additions, meaning they appear in the modified text but not in the original. Red lines with a minus prefix represent removals, meaning they were in the original but are absent from the modified version. Gray or muted lines are unchanged and appear identically in both texts. This color scheme follows the universal convention used by Git, GitHub, and virtually every code review platform.
Practical Applications
Content teams use diff checkers to review editorial changes before publishing. Configuration management requires comparing server configs to detect drift. Database administrators compare schema definitions across environments. Quality assurance teams compare API responses between staging and production. Students compare essay drafts to track their revision progress. Data analysts compare CSV exports to identify changed records.
Privacy and Security
All comparison processing happens entirely in your browser. Neither the original nor the modified text is transmitted to any server. This makes the tool safe for comparing sensitive documents, proprietary code, confidential contracts, and personal information. You can verify this by monitoring your browser network tab during usage.