Diff Checker
Compare text and find differences
Diff Checker
This tool helps you compare text and find the differences between two files.
Original Text
Modified Text
Difference Result
How to use the Diff Checker
- •Paste your original text into the left panel labeled "Original" or "Before." This serves as the baseline for comparison.
- •Paste the modified text into the right panel labeled "Modified" or "After." This is the version you want to compare against the original.
- •Review the highlighted differences. Added lines appear in green, removed lines appear in red, and changed lines show both the old and new versions with inline highlighting of the exact characters that differ.
- •Toggle between unified and side-by-side views to choose the comparison layout that best suits your needs. Unified view is more compact; side-by-side makes it easier to scan large changes.
What is a Diff?
A "diff" is the computed difference between two pieces of text. The concept originated in the Unix utility diff, written by Douglas McIlroy in 1974, which compares files line by line and outputs the minimum set of changes needed to transform one file into the other.
Modern diff algorithms, such as the Myers diff algorithm (used by Git), find the longest common subsequence between two texts and then identify the insertions and deletions needed to get from one to the other. This is the same algorithm that powers git diff, pull request reviews on GitHub, and code review tools everywhere.
Diffs are represented using a standard notation:
- •Lines starting with
+were added in the new version - •Lines starting with
-were removed from the old version - •Lines without a prefix are unchanged and provide context
Understanding diffs is fundamental to version control. Every Git commit stores a diff (technically a snapshot, but diffs are how changes are displayed). Code reviews on platforms like GitHub, GitLab, and Bitbucket are essentially structured diff viewers with the ability to leave comments on specific changed lines.
Beyond code, diffs are useful for comparing any text: legal contracts, configuration files, translated documents, or even prose. If you need to know exactly what changed between two versions of anything, a diff is the answer.
Common use cases
- •Code review preparation: Compare your local changes before committing to ensure you are only including the intended modifications.
- •Configuration auditing: Compare two versions of a config file (nginx.conf, docker-compose.yml, .env) to spot unintended changes before deploying.
- •Content editing: Compare draft versions of articles, documentation, or legal documents to see exactly what was added, removed, or reworded.
- •Debugging: When a previously working feature breaks, diff the current code against a known good version to quickly identify what changed.
- •Merge conflict resolution: Paste the conflicting sections side by side to understand both versions before deciding how to resolve the conflict.
FAQ
Q: Does the diff checker work with very large files? A: The tool handles files of several thousand lines comfortably. For extremely large files (tens of thousands of lines), performance depends on your browser's memory. Consider comparing only the relevant sections if you encounter slowdowns.
Q: Can I compare binary files or images? A: No. This tool is designed for plain text comparison. For binary or image diffs, use specialized tools like Git LFS diff drivers or dedicated image comparison software.
Q: What algorithm does this use? A: The tool uses a variant of the Myers diff algorithm, the same algorithm used by Git. It computes the shortest edit script to transform one text into the other, producing clean and minimal diffs.
Is my data safe?
Yes. This tool runs entirely in your browser. Your data is never sent to our servers.
How to use the Diff Checker
- Paste your original text into the left panel labeled "Original" or "Before." This serves as the baseline for comparison.
- Paste the modified text into the right panel labeled "Modified" or "After." This is the version you want to compare against the original.
- Review the highlighted differences. Added lines appear in green, removed lines appear in red, and changed lines show both the old and new versions with inline highlighting of the exact characters that differ.
- Toggle between unified and side-by-side views to choose the comparison layout that best suits your needs. Unified view is more compact; side-by-side makes it easier to scan large changes.
What is a Diff?
A "diff" is the computed difference between two pieces of text. The concept originated in the Unix utility diff, written by Douglas McIlroy in 1974, which compares files line by line and outputs the minimum set of changes needed to transform one file into the other.
Modern diff algorithms, such as the Myers diff algorithm (used by Git), find the longest common subsequence between two texts and then identify the insertions and deletions needed to get from one to the other. This is the same algorithm that powers git diff, pull request reviews on GitHub, and code review tools everywhere.
Diffs are represented using a standard notation:
- Lines starting with
+were added in the new version - Lines starting with
-were removed from the old version - Lines without a prefix are unchanged and provide context
Understanding diffs is fundamental to version control. Every Git commit stores a diff (technically a snapshot, but diffs are how changes are displayed). Code reviews on platforms like GitHub, GitLab, and Bitbucket are essentially structured diff viewers with the ability to leave comments on specific changed lines.
Beyond code, diffs are useful for comparing any text: legal contracts, configuration files, translated documents, or even prose. If you need to know exactly what changed between two versions of anything, a diff is the answer.
Common use cases
- Code review preparation: Compare your local changes before committing to ensure you are only including the intended modifications.
- Configuration auditing: Compare two versions of a config file (nginx.conf, docker-compose.yml, .env) to spot unintended changes before deploying.
- Content editing: Compare draft versions of articles, documentation, or legal documents to see exactly what was added, removed, or reworded.
- Debugging: When a previously working feature breaks, diff the current code against a known good version to quickly identify what changed.
- Merge conflict resolution: Paste the conflicting sections side by side to understand both versions before deciding how to resolve the conflict.
FAQ
Q: Does the diff checker work with very large files? A: The tool handles files of several thousand lines comfortably. For extremely large files (tens of thousands of lines), performance depends on your browser's memory. Consider comparing only the relevant sections if you encounter slowdowns.
Q: Can I compare binary files or images? A: No. This tool is designed for plain text comparison. For binary or image diffs, use specialized tools like Git LFS diff drivers or dedicated image comparison software.
Q: What algorithm does this use? A: The tool uses a variant of the Myers diff algorithm, the same algorithm used by Git. It computes the shortest edit script to transform one text into the other, producing clean and minimal diffs.
Is my data safe?
Yes. This tool runs entirely in your browser. Your data is never sent to our servers.