How to Use a Text Diff Tool | Instantly Spot Differences Between Two Texts

"What exactly changed between the old version and the new one?" — Finding differences between two texts by eye is far more time-consuming than most people expect. This article covers everything from the basics of using a diff tool to practical use cases including contract review, code review, and proofreading.

How to Use a Text Diff Tool

Basic Usage

1. Paste the original text on the left side
2. Paste the modified text on the right side
3. Differences are automatically highlighted

Changes are color-coded for instant clarity:

• Red (deletion): Text present in the original but removed in the modified version
• Green (addition): Text newly added in the modified version

Switching Display Modes

sakutto's text diff tool offers two display modes:

Using the Merge Feature

The tool also includes a merge feature that lets you choose which side to keep for each detected difference.

1. Click the merge button at a diff location
2. Select which side to keep
3. Your selection is applied

The merge feature is especially useful when you want to cherry-pick the best parts from two versions — for example, combining edits from two proofreaders, or selectively adopting changes from a refactored codebase.

Character-Level Diff Detection

sakutto's diff tool detects differences at the character level. Instead of highlighting entire lines, it pinpoints exactly which characters changed within a line.

For example, if "123 Main Street" changes to "123 Oak Street", only "Main" and "Oak" are highlighted — the shared parts "123 " and " Street" remain unhighlighted.

Use Case Guide

Reviewing Contract and Terms Changes

Checking what changed in a contract draft from a business partner is a critical task. Here's how to do it:

Steps:

1. Paste the previous version of the contract on the left
2. Paste the new version on the right
3. Review each highlighted change one by one

This also works well for comparing old and new versions of terms of service to quickly identify changes, especially in privacy policies.

Checking Meeting Notes and Document Revisions

When you receive a revised version of meeting notes, you can quickly see what changed from the original draft. For manuals and procedure documents, recording diffs when making updates creates a useful change history.

Code Review and Config File Comparison

While GitHub and GitLab have built-in diff features, a browser-based diff tool is invaluable for these scenarios:

• Code outside Git: Spreadsheet macros, database stored procedures
• Config file comparison: Checking differences between .env or nginx.conf files across production and test environments
• SQL query comparison: Reviewing changes in WHERE clauses or JOIN conditions
• API response comparison: Comparing previous JSON responses with the latest version

sakutto's diff tool uses a monospace font, making code diffs easy to read and indentation changes easy to spot.

Review workflow for projects without Git:

1. The author shares before and after versions of the file
2. The reviewer compares them using sakutto's diff tool
3. The reviewer records comments for each change and provides feedback

Proofreading and Editing

When an editor returns a proofread manuscript, you can see at a glance what was changed. For documents going through multiple rounds of editing — first draft, second draft, third draft — comparing diffs at each stage lets you track the progression of changes.

Key things to check:

• Were any factual corrections made?
• Were there any changes in nuance?
• Were typo corrections applied as intended?

Translation and Localization

When source text is updated, comparing it with the previous version helps identify which sections need re-translation. It's also useful for comparing past and new translations to verify terminology consistency.

CSV Data and Config File Integrity Checks

Compare exported CSV data before and after updates to identify changed rows or values. Check differences between production and test environment configuration files to ensure consistency.

Tips for Effective Diff Comparison

Tip 1: Normalize Formatting Before Comparing

Standardize formatting (line breaks, spaces, etc.) between the two texts to avoid meaningless diffs. If a code refactoring only changed indentation, normalize indentation first to focus on substantive changes.

Tip 2: Compare Section by Section

Comparing an entire long document at once can produce overwhelming results. Breaking it into sections makes the review more manageable.

Tip 3: Use Navigation to Review Changes

Jump between changes using the arrow buttons and review each one systematically to avoid missing anything.

Tip 4: Use Merge for Gradual Integration

When combining large refactors or edits from multiple people, use the merge feature to select which version to keep for each change, building the final version incrementally.

FAQ

Is the text I enter sent to a server?

No, all processing happens entirely in your browser. The text you enter is never sent to any server. You can safely use it for confidential documents and contracts.

Does it support Japanese text?

Yes, it fully supports Japanese text. Hiragana, katakana, kanji, and full-width symbols are all accurately detected in the diff.

How long can the compared texts be?

The tool can handle tens of thousands of lines with fast diff detection. For typical documents and code, it works seamlessly, and the navigation feature lets you jump between changes efficiently.

Can I compare Word or PDF files directly?

The tool compares text content. For Word or PDF files, copy the content and paste it as text. Formatting information (bold, font size, etc.) is not included in the comparison.

Does it work on mobile?

Yes, it works in mobile browsers. On mobile devices, it automatically switches to unified (inline) view for comfortable diff reviewing.

Does it support syntax highlighting?

Syntax highlighting is not supported, but the monospace font makes code diffs easy to read. If you need language-specific highlighting, consider using VS Code's built-in diff feature alongside sakutto.

Summary

A text diff tool lets you instantly highlight differences between two texts. It's useful for a wide range of tasks — contract reviews, meeting note checks, code reviews, proofreading, translation verification, and data integrity checks. sakutto offers character-level diff detection and merge functionality, and since no data is sent to a server, it's safe for confidential documents.