Diff Checker
Compare two texts side by side and find the differences instantly.
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Paste text in both fields above or load a sample
Introduction
Spotting the difference between two versions of a contract, configuration file, or source code listing by eye is unreliable once the content exceeds a few dozen lines. A diff checker computes the exact lines that were added, removed, or modified between two text inputs using the same Longest Common Subsequence algorithm that powers git diff. The visual highlight makes it immediately obvious whether a collaborator changed a single number in a pricing clause or rewrote an entire paragraph — no more squinting at side-by-side printouts.
What Is Diff Checker?
A diff checker is a comparison utility that takes two text inputs — original and modified — and produces an annotated view showing exactly what changed. It uses the Myers diff algorithm to find the minimal set of insertions and deletions that transform the original text into the modified text, then renders the result with color-coded highlights: green for added lines, red for removed lines, and yellow for changed words within modified lines.
The tool supports three view modes. Unified diff shows all changes in a single scrollable panel with + and - prefixes, matching the format developers know from git diff output. Side-by-side diff places the original and modified texts in adjacent columns so you can visually scan both versions simultaneously. Inline diff overlays changes within a single text block, which is ideal for reviewing prose changes in legal documents or marketing copy where line-by-line alignment matters less than reading the full revised text.
Beyond line-level granularity, the word-level diff detects changes within a line. For example, if a line changes from "The project deadline is March 15" to "The project deadline is April 20," only the words "March 15" and "April 20" are highlighted, making the specific change immediately visible without reading the entire line. This is particularly useful for reviewing JSON or YAML configuration files where a single changed value in a long line can be easy to miss.
Diff Checker Examples
| Input | Output |
|---|---|
| v1: "port: 8080" vs v2: "port: 3000" | Word diff highlights "8080" (removed) and "3000" (added) |
| Contract v1 vs v2 (12 paragraphs, 3 changed) | 3 paragraphs highlighted with added/removed lines and changed words |
| config.yaml (50 lines) vs config_new.yaml | Unified diff: -2 lines, +2 lines, 3 unchanged sections collapsed |
Key Features of Diff Checker
- Myers diff algorithm producing the minimal edit sequence between original and modified texts
- Three view modes: unified diff, side-by-side comparison, and inline overlay
- Word-level change highlighting within modified lines for pinpointing exact value changes
- Ignore whitespace and ignore case options for comparing content regardless of formatting differences
- Line numbers displayed for both versions to cross-reference changes in longer documents
- File upload support for comparing two text files directly without copy-pasting contents
- Statistics panel showing total lines added, removed, and unchanged at a glance
How It Works
Paste Both Versions of Your Text
Enter the original text in the left panel and the modified version in the right panel. The diff checker works with any line-based content including source code, configuration files, legal documents, articles, and data exports where you need to identify exactly what changed.
Line-by-Line Comparison with Highlighting
The tool performs a structural diff algorithm that compares both texts line by line. Inserted lines are highlighted in green, deleted lines in red, and unchanged lines appear in neutral formatting. This visual coding makes it immediately clear what was added, removed, or modified between the two versions.
Review and Share the Comparison
Scroll through the diff output to review every change in context. The side-by-side view shows both versions with synchronized scrolling so you can see what each line looked like before and after the edit, making it easy to verify that changes are correct and intentional.
Who Uses This
Legal Professionals
comparing revised contract drafts to verify that only agreed-upon changes were made and no additional clauses were silently inserted between negotiation rounds
Editors and Publishers
tracking changes between manuscript revisions to see exactly what the author added or removed, ensuring editorial feedback was properly addressed without losing intended content
Configuration Managers
diffing server configuration files before and after changes to verify that only the intended settings were modified and no accidental edits were introduced during maintenance windows
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