Free Diff Checker - Compare Text Differences

Find differences between two texts, code snippets, or documents with character-level highlighting. Side-by-side, inline, and unified-style views.

Diff Checker: Paste the original text in the left panel and the modified text in the right panel. The tool instantly shows differences with color-coded highlighting — red for removed lines, green for added lines, with character-level highlighting inside changed lines. Switch between side-by-side, inline, and unified-style views. Toggle 'Ignore whitespace' or 'Ignore case' for cleaner comparison. Copy or download the diff text as a .diff file.

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Key Takeaways

Three view modes: side-by-side (classic diff), inline (sequential changes), and unified-style diff output
Character-level diff highlighting shows exact changes within modified lines — not just line-level red/green
Ignore whitespace and ignore case options for semantic comparison that ignores trivial formatting differences
LCS-based diff algorithm works with plain text, code, JSON, CSV, logs, and configs
Browser-side comparison keeps the pasted text in the page during diff generation
Copy the generated diff text or download it as a .diff file

What is Diff Checker?

Diff Checker — A diff checker is a tool that compares two pieces of text — code, documents, or any string content — and highlights the differences line by line and character by character, showing what was added, removed, or changed between the two versions.

This diff checker compares two pieces of text and highlights their differences in real time. Paste your original text on the left and the modified version on the right, and the tool computes a diff using an LCS (Longest Common Subsequence) algorithm. Changes are shown with color coding: red for removed lines, green for added lines, and plain for unchanged content. Character-level highlighting within modified lines shows exactly what changed — not just the entire line. Toggle between three views: side-by-side (classic diff view), inline (sequential changes), or unified-style diff output. Options to ignore whitespace and case help you focus on meaningful differences. The diff text can be copied to clipboard or downloaded as a .diff file.

How to Use Diff Checker

1
Paste or type the original text into the left 'Original Text' panel.
2
Paste or type the modified text into the right 'Modified Text' panel. The diff updates in real time below.
3
Toggle 'Ignore whitespace' or 'Ignore case' in the options if you want to focus on semantic changes only.
4
Switch between Side by Side, Inline, and Unified view modes depending on how you want to review the differences.
5
Click 'Copy Diff' to copy the unified-style output to your clipboard, or 'Download' to save it as a .diff file.

Key Features

Three View Modes: Side-by-side (original | modified), inline (sequential with +/- markers), and unified-style output with --- and +++ headers.

Character-Level Highlighting: When a line is modified, the exact characters that changed are highlighted inside the line — not just the whole line in red/green. This makes small changes instantly visible.

Ignore Whitespace: Toggle to ignore tabs, spaces, and line-break differences — useful for comparing code that's been reformatted or text that's been re-wrapped.

Ignore Case: Toggle case-insensitive comparison — useful for comparing text where casing shouldn't matter (like emails, keywords, or titles).

Real-Time Statistics: Live counters show added lines, removed lines, and unchanged lines as you type or paste.

Line Numbers: Both panels show original and modified line numbers for precise reference.

LCS Diff Algorithm: Uses Longest Common Subsequence to identify added, removed, and unchanged lines.

Unicode Support: Works with Unicode text including multi-byte characters and emojis.

Copy Diff: One-click copy of the unified-style diff text to clipboard.

Download Diff: Save the generated diff text as a .diff file for review or sharing.

Swap Texts: Quickly swap the original and modified panels with one click.

Browser-Side Comparison: The diff calculation runs in the page after your text is pasted.

Use Cases

Code Review: Compare before/after versions of code to see exactly what a change does — useful for pull request reviews outside of a Git GUI.

Document Versioning: Compare two versions of a document (contract, resume, manuscript) to see what was edited.

Log File Analysis: Diff two log files or config files to identify what changed between deploys.

Content Editing: Writers and editors use diff tools to review changes between draft versions.

Translation QA: Compare source and translated text to verify structure and find missing sections.

SEO Content Updates: Compare old and new versions of page content to track changes for SEO audits.

JSON / YAML / Config Diffs: Compare configuration files to spot differences between environments.

Email Drafts: Compare two versions of an email or proposal before sending.

Database Migrations: Compare SQL schema files to identify migration deltas.

About Diff Checker

How Diff Algorithms Work

This tool uses an LCS (Longest Common Subsequence) algorithm to compute diffs — the same mathematical foundation used by Git, Unix diff, and most code review tools. LCS finds the longest sequence of lines that appear in both texts in the same order, and classifies everything else as either added or removed. This produces minimal diffs — the smallest possible set of changes that transform the original into the modified text. Character-level highlighting applies the same algorithm to individual characters within changed lines, so you can see exactly what changed down to the letter.

Side-by-Side vs Inline vs Unified View

Side-by-side view (classic diff) shows original on the left and modified on the right in parallel columns — best for reviewing large changes where spatial context matters. Inline view shows all changes sequentially in one column with +/- markers — better for small screens and quick scanning. Unified view uses --- and +++ headers with added and removed line prefixes, which is useful for compact review, copying, and sharing. Choose the view that matches your workflow.

When to Use Ignore Whitespace & Ignore Case

Ignore whitespace treats all runs of whitespace (spaces, tabs, line endings) as equivalent — this is essential when comparing code that's been reformatted by Prettier, ESLint, or Black, or text that's been re-wrapped to a different line width. Without this option, you'd see every line as changed even though the content is identical. Ignore case makes the comparison case-insensitive — useful for comparing email addresses, keywords, URLs, or any text where casing is not semantically meaningful.

Privacy and Security

The comparison runs in your browser using JavaScript, so the tool does not need to send pasted text to a diff-processing API. That is useful for quick checks of code, contracts, drafts, and configuration files. For highly confidential or regulated material, follow your organization's policy before pasting content into any web page.

Diff Algorithm Notes

This tool uses a dynamic-programming LCS comparison for lines, and then applies a character-level comparison inside paired changed lines. Other developer tools may use different algorithms depending on the workflow:

LCS line diff: the method used here to mark lines as unchanged, added, or removed.
Myers diff: common in command-line diff tools and source-control workflows.
Patience and histogram diff: useful in some Git workflows when code blocks have moved.
Word-level diff: useful for prose changes where line breaks would otherwise mark whole paragraphs as different.
Character-level diff: what this tool uses within changed lines to show exact letter-level changes.

Diff Checker vs Git, GitHub PRs, VS Code, Beyond Compare

Tool	Best for	Limitations
This tool	Ad-hoc text comparison, sensitive content, quick paste-and-compare	No file upload, no Git integration
Git diff CLI	Within a Git repo, scriptable	Requires Git context; terminal only
GitHub PR view	Team code reviews with comments	Requires GitHub; tied to commits
VS Code Compare	Live editing during comparison	Needs files on disk; editor open
Beyond Compare (paid)	3-way merge, folder diffs, FTP/SCP	$60+ per license
Dedicated hosted diff services	Saved comparisons, file uploads, extra media formats	May be more than you need for a quick pasted-text comparison
Meld (Linux)	3-way merge, folder comparison	Desktop install required

Unified-Style Diff Output

The unified view gives a compact text representation with file-style headers and line prefixes:

--- Original
+++ Modified
 unchanged line above
-removed line
+added line
 unchanged line below

The header lines (--- / +++) identify the two sides. Lines prefixed with - were removed, + were added, and unprefixed lines are unchanged context. The downloaded .diff file is intended for review, sharing, or archiving; it is not a generated Git patch with hunk line ranges.

Common Use Cases Beyond Code Review

Contract / legal document comparison: compare versions of contracts, NDAs, terms of service to spot changed clauses. Use character-level highlighting to catch single-word changes.
Manuscript editing: compare draft 1 vs draft 2 of an article / book chapter / paper
Translation QA: compare source and translated text to verify structure preservation and find missing sections
Config file environments: compare dev / staging / prod configs to find drift
Log file analysis: compare last week's logs vs this week's to find new error patterns
SQL query comparison: compare two query versions during optimization to see exactly what changed
API response comparison: compare what an API returned today vs what it returned last month (use Ignore Whitespace + sort first for stable comparison)
Email draft review: compare a teammate's edits to your draft
Plagiarism detection: compare two essays to identify identical passages
Resume version tracking: see what you changed between job application versions

Frequently Asked Questions

What is a diff checker?: A diff checker is a tool that compares two pieces of text (code, documents, configs, or any strings) and highlights the differences — showing what was added, removed, or changed. It's the same type of tool built into Git, code review platforms, and text editors, but works standalone in your browser for any text you paste.
Is this diff checker free?: Yes. You can compare pasted text directly in the browser and use the side-by-side, inline, unified-style, copy, and download options without creating an account.
Is my text private?: Yes. This diff checker runs entirely in your browser using JavaScript. Your text is never uploaded to any server, never logged, and never stored. You can safely use it for proprietary code, legal contracts, medical records, or any sensitive content.
How do I compare two text files?: Paste the original text into the left panel and the modified text into the right panel. The diff updates automatically as you type. You can then switch between side-by-side, inline, or unified views, and toggle ignore whitespace or ignore case for cleaner results.
What's the difference between side-by-side, inline, and unified views?: Side-by-side shows original and modified in parallel columns — best for spatial comparison. Inline shows all changes sequentially with + and - markers — better for narrow screens. Unified shows a compact diff-style text view with --- and +++ headers.
Does it work with code, JSON, or CSV?: Yes. The diff checker works with any text content including source code (all languages), JSON, YAML, XML, CSV, SQL, logs, config files, and prose. It does line-level and character-level comparison on any text.
What is character-level highlighting?: When a line is modified, character-level highlighting shows exactly which characters changed inside that line — not just the entire line in red/green. For example, if you change 'console.log(a)' to 'console.log(b)', only the 'a' → 'b' change is highlighted, making small changes instantly visible. This is enabled by default.
What does 'Ignore whitespace' do?: Enabling 'Ignore whitespace' treats all runs of spaces, tabs, and line endings as equivalent. This is essential when comparing code that's been reformatted by Prettier, ESLint, or Black — otherwise you'd see every line flagged as changed even though the content is identical.
Can I download the diff output?: Yes. Click 'Download' to save the generated diff text as a .diff file. You can also click 'Copy Diff' to copy the same output to your clipboard.
Is there a file size limit?: There is no separate upload limit because you paste text into the page, but performance depends on browser memory, device speed, and text size. Very large files are better compared with Git, a desktop editor, or a command-line diff tool.
Can I use this to compare code in a pull request workflow?: Yes. Paste the before and after versions of your code to see a text diff with character-level highlighting. Use 'Ignore whitespace' to filter out reformatting noise, then copy or download the diff text for review.
Does it support Unicode and emojis?: Yes. The LCS diff algorithm works at the character level with full Unicode support, including multi-byte characters, emojis, Chinese, Arabic, Hindi, and other scripts. Mixed-direction text (LTR + RTL) also renders correctly.

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