Text Diff Checker

About Text Diff

A diff (short for difference) highlights the exact changes between two versions of text. Lines present only in the original are shown in red, lines only in the modified version in green, and matching lines in gray. This is the same concept used by Git, code review tools, and version control systems.

Use Cases

Compare code changes, contract revisions, configuration files, translated texts, or any two pieces of text. The entire comparison runs locally in your browser — nothing is uploaded.

Understanding Diff Output

When you click Compare, the tool runs a line-by-line diff algorithm based on the Longest Common Subsequence (LCS) — the same core method used by Unix diff and Git diff. The algorithm works in two phases: first it builds a dynamic-programming table to find the longest sequence of lines common to both texts in the same order, then it backtracks through that table to determine which lines were added, removed, or left unchanged. This guarantees an optimal minimal edit script, meaning the tool always produces the most compact representation of your changes.

The output is color-coded for instant scanning:

• Green lines preceded by a plus sign (+) represent additions — text that exists in the modified version but not in the original.
• Red lines preceded by a minus sign (−) represent deletions — text that was present in the original but removed from the modified version.
• Gray lines with a blank marker represent unchanged text — lines common to both versions that provide surrounding context.

A summary bar below the output shows the total count of added, deleted, and unchanged lines so you can assess the scope of changes at a glance. You can also copy the unified diff output to share with your team or paste into a commit message.

When to Use a Text Diff Tool

A text diff is one of the most universally useful utilities for anyone working with written content. Common scenarios include:

• Code reviews — Quickly spot what changed between pull request iterations without re-reading entire files. Pair this with the Regex Tester to validate pattern changes side by side.
• Contract and document comparison — Verify that only intended changes were made between drafts, catching unwanted modifications before finalization.
• Configuration file auditing — Compare old and new .env, nginx.conf, docker-compose.yml, or .gitignore files to verify deployment changes.
• Plagiarism and similarity checks — Paste suspect text alongside the original to see exactly which passages match and which were reworded.
• Version control without Git — When you only have two files and no repository history, this tool acts as a standalone diff viewer. Use the JSON Formatter to prettify structured data before running a diff for cleaner comparisons.
• Translation review — Compare source and translated strings line by line to verify completeness across languages.

Because all processing happens client-side in your browser, your text never leaves your machine — making this tool safe for sensitive documents, proprietary source code, and confidential contracts.