📝 Text Diff Checker
Compare two texts and see exactly what changed. Line-by-line diff with color-coded additions and deletions. Free, no signup.
Compare two texts and see every difference highlighted instantly. Additions appear in green and deletions in red with clear line-by-line alignment. Each line is compared individually — paste any text to check revisions, code changes, or document edits. Useful for developers, writers, and editors reviewing changes.
📋 When to Use the Text Diff Checker
This tool is for anyone comparing two versions of text and needing to see exactly what changed — line by line. Real scenarios where a visual diff saves time and prevents errors:
- Code review preparation: Before submitting a pull request, compare your branch changes against the base to verify only intended modifications. Paste both versions and get an instant line-level diff.
- Configuration file comparison: Server configs (.env, docker-compose, nginx.conf) drift across environments. Paste the staging and production versions to spot discrepancies — changed ports, missing keys, or accidental typos.
- Document and contract revision tracking: Authors and editors track changes between document drafts. Paste the original and revised paragraphs to see which lines were rewritten, added, or removed — no need to read both documents manually.
- Translation verification: Compare source text against the translated version to confirm line count and structure match. Useful for UI strings, subtitles, or legal translations where every line must correspond.
- Log output comparison: After a deployment, compare today's error log against yesterday's to surface new exceptions without scanning hundreds of lines manually. Paste both logs and let the diff highlight what's new.
- Copy-paste integrity check: When moving code or text between tools (IDE → email, terminal → documentation), paste both versions to catch accidental omissions, extra blank lines, or formatting corruption.
No signup, no uploads — paste, click, and see the diff instantly in your browser.
⚙️ How the Text Diff Checker Works
This tool compares two texts line by line using the Longest Common Subsequence (LCS) algorithm — implemented in plain JavaScript with no external libraries or API calls. Here's the full process:
- Split into lines: Both texts are split at every newline character, creating two arrays: original lines and modified lines.
- Build the DP table: A 2D dynamic programming table
dp[i][j]is filled. Each cell records the length of the longest common subsequence between the firstioriginal lines and firstjmodified lines. Building the table takes O(m×n) time and space. - Backtrack for the diff: Starting from the bottom-right cell, the algorithm traces back: diagonal moves mean lines matched (unchanged), left moves mean a line was inserted (only in modified), and up moves mean a line was deleted (only in original).
- Render with color coding: The resulting diff sequence is converted to HTML. Inserted lines appear in green with a + sign, deleted lines in red with a − sign, and unchanged lines in gray.
The comparison uses exact line equality (=== in JavaScript). If any character differs — even a trailing space or different capitalization — the entire line is treated as changed. There is no character-level or word-level highlighting within a line. All computation runs in your browser; no text is sent to any server.
How to Use the Diff Checker
- Paste your original text in the left panel and the modified text in the right panel.
- Click 'Compare' or let the auto-diff run as you type.
- Differences are highlighted: green for additions, red for deletions.
- Review the unified diff — all lines from both texts in one column, color-coded. Copy the results for documentation, code reviews, or commit messages.
Frequently Asked Questions
How does the diff algorithm work?
The tool uses a Longest Common Subsequence (LCS) algorithm implemented in pure JavaScript. Both texts are split into lines, a 2D dynamic programming table finds the longest matching sequence, and backtracking classifies each line as added (green), removed (red), or unchanged (gray).
Is the diff line-by-line or character-by-character?
Line-by-line only. If two lines differ by even a single character — an extra space, different capitalization — the entire line is marked as changed. There is no inline character-level highlighting. For character-level diffs, use git diff --word-diff or a dedicated merge tool.
Does it ignore whitespace or case?
No. The comparison uses exact JavaScript equality (===). Leading/trailing spaces, tabs, and letter casing all count as differences. A line with an extra trailing space will show as changed. Normalize your text beforehand in an editor or using our Case Converter if needed.
Is there a text size limit?
Yes. Each side is capped at ~1 MB (2 MB combined) to keep the browser responsive; larger inputs are rejected with a message. Comparisons under ~2,000 lines are instant, and LCS uses O(m×n) memory so bigger inputs get slower. For files too large to paste, use diff / git diff in the terminal instead.
Can I see the diff side by side?
Not currently. The tool shows a unified diff — a single vertical list with all lines from both texts, color-coded by status. Deleted lines (red, −) and inserted lines (green, +) appear interleaved in one column, similar to git diff output.
Does this tool work offline?
Yes. The LCS diff algorithm is pure JavaScript with no CDN or API dependencies. Once the page loads, you can disconnect from the internet and the comparison still works. Ad scripts and analytics are non-essential — they don't affect the core diff functionality.