Diff Checker

Compare two texts and see every difference in a Git-style diff view with inline word highlights

Word-level diff | 100% client-side
Original
Modified
diff --text a/original b/modified
--- a/original
+++ b/modified
Original
Modified
Paste text in both panels to compare
Auto-compare as you type | Your data never leaves your browser

What Is a Diff Checker?

Understanding text comparison and how diff tools help you track changes

A diff checker (short for "difference checker") is a tool that compares two blocks of text and identifies the differences between them line by line. It highlights which lines have been added, removed, or left unchanged, giving you a clear visual summary of how one version of a document differs from another.

Diff tools are essential in software development, content editing, and document management. The concept originated with the Unix diff command in the 1970s and is the foundation of modern version control systems like Git. Today, diff checking is used to review code changes, verify edits, audit configurations, and maintain an accurate history of modifications over time.

Word-Level Precision

Beyond line-by-line comparison, this tool highlights the exact words that changed within modified lines, making it easy to spot single-character edits in long lines of code or text.

Git-Style Output

The diff output uses a dark terminal theme with the familiar +/- prefix notation, color coding, and file headers that developers know from git diff.

100% Client-Side

Your text never leaves your browser. All comparison logic runs entirely in JavaScript on your device, so sensitive content like source code or contracts stays completely private.

How to Use the Diff Checker

Follow these simple steps to compare your texts in seconds

1

Paste or Import

Paste the original text on the left and the modified text on the right. Or use the upload buttons to import files directly.

2

Configure Options

Toggle "Ignore Whitespace" to skip formatting-only changes. Use "Swap" to switch original and modified texts.

3

Review the Diff

The diff renders automatically in a Git-style dark terminal view. Green = added, red = removed, with word-level highlights.

4

Copy or Navigate

Toggle Split/Unified views, navigate between changes with arrow buttons, or copy the entire diff output to your clipboard.

Common Use Cases

See how developers, writers, and teams use diff checking every day

Code Review

Compare two versions of a source file before committing or merging. Spot accidental deletions, logic changes, or formatting inconsistencies with word-level precision.

Document Editing

Track changes in contracts, articles, or reports. Compare drafts to see exactly what was added, removed, or reworded between revisions.

Configuration Auditing

Compare server configs, environment files, or infrastructure-as-code templates to catch unintended changes before deploying to production.

Data Comparison

Compare CSV exports, SQL dumps, JSON responses, or log files to identify record-level changes. Useful for debugging data pipelines or verifying migration results.

Debugging API Responses

Compare API responses across environments (staging vs production) or across time to identify exactly which fields changed, helping you pinpoint bugs faster.

Translation Verification

Compare translated text files or localization resource files (e.g. i18n JSON) to ensure no keys were accidentally removed or added during the translation process.

Frequently Asked Questions

Common questions about the diff checker and text comparison

A diff checker is a tool that takes two blocks of text and compares them line by line. It highlights added lines (present only in the modified text), removed lines (present only in the original text), and unchanged lines (identical in both). This makes it easy to review changes between two versions of any document or code file.
Yes. This diff checker runs entirely in your browser using JavaScript. Your text is never sent to a server. All comparison logic is executed client-side, so your data stays on your device and is never stored or transmitted. You can verify this by checking the Network tab in your browser's Developer Tools.
The tool uses a Longest Common Subsequence (LCS) algorithm, which is the same foundational approach used by Unix diff and Git. It finds the longest sequence of lines common to both inputs, then marks the remaining lines as additions or deletions to produce a minimal, accurate diff.
Yes. When a line is modified (not purely added or removed), the tool performs a word-level diff within that line. The exact words that changed are highlighted with a darker background color, making it easy to spot small edits within long lines of code or prose.
Side by Side view shows the original text on the left and the modified text on the right, making it easy to visually scan differences in parallel. Unified view combines both texts into a single column, prefixing removed lines with - and added lines with +, similar to the output of git diff.
When enabled, the Ignore Whitespace option trims leading and trailing whitespace from each line and collapses multiple consecutive spaces into a single space before comparing. This is useful for comparing code where indentation style may have changed (tabs vs. spaces, 2-space vs. 4-space) but the actual logic is identical.
Yes. Each input panel has an upload button (arrow icon) that lets you import any text-based file directly — including .txt, .json, .yaml, .py, .js, .php, .sql, .csv, and more. The file contents will be loaded into the corresponding text area.
This tool works well with moderately sized texts (up to several thousand lines). Because the diff is computed in the browser, very large files (tens of thousands of lines) may cause the browser to slow down. For extremely large files, a desktop tool like Beyond Compare, Meld, or the git diff command may be more appropriate.