Free Tool
Diff Checker
Paste two text blocks and see exactly what changed — line-by-line with added and removed lines clearly highlighted. Uses LCS algorithm. Free, no sign-up, runs in your browser.
Diff Checker
What is a diff checker?
Diffing compares two text blocks line by line and highlights which lines were added, removed, or unchanged. This makes it easy to spot changes in config files, code reviews, or copy edits.
How the algorithm works
This tool uses LCS (Longest Common Subsequence) diffing — the same foundation as git diff. It finds the minimal set of changes between the two texts.
Limitations
This is a text-only line diff. It does not understand code syntax, whitespace-only changes will appear as changes, and it does not support three-way merges.
How to use
- Paste your original text into the left panel.
- Paste the modified text into the right panel.
- The diff view updates instantly, highlighting added lines in green and removed lines in red.
- Use the stats summary at the top to see total added, removed, and unchanged line counts.
Examples
- Simple: Paste two versions of a
config.json— one with"timeout": 30and the other with"timeout": 60. The changed line is highlighted in red (removed) and green (added). - Developer workflow: Compare an API response before and after a schema migration. Paste the old and new JSON payloads to spot added or removed fields instantly.
- Edge case: Whitespace-only changes (extra spaces, trailing newlines) still show as diffs. If your diff looks unexpectedly large, check for trailing whitespace differences.
Frequently Asked Questions
- What is a diff checker?
- A diff checker compares two text files or strings and shows the differences between them — which lines were added, removed, or unchanged. It is widely used by developers to review code changes, compare configuration files, and track document revisions.
- What algorithm does this diff checker use?
- This tool uses the Longest Common Subsequence (LCS) algorithm, the same underlying approach used by Git's diff. It finds the optimal set of changes — the minimum number of lines that need to be added or removed to transform text A into text B.
- How do I read the diff output?
- Lines marked with + (green) exist only in the changed version (B). Lines marked with − (red) exist only in the original version (A). Lines with no marker are unchanged and appear in both.
- Is my text kept private?
- Yes. All comparison happens in your browser — no text is sent to any server. Your data never leaves your device.