Text Diff

What is this tool?

This text diff tool compares two plain texts side by side or in a unified diff view. You paste or type content in Original (left) and Modified (right); the tool highlights line-by-line differences—additions in green, removals in red—so you can see exactly what changed. It works for logs, configs, code snippets, SQL, Markdown, or any two text blobs. You can swap sides, resize the panels, copy the diff, download it, or share a link that encodes both texts. All processing runs in your browser—your data is not sent to a server.

Why use a text diff tool?

Comparing two versions of a file, log, or snippet by eye is tedious and error-prone. A text comparison tool highlights added and removed lines at a glance, so you can review changes before committing, debug config differences between environments, or compare API responses and build outputs. Unlike a JSON diff (which compares by structure and keys), this tool treats input as plain text and diffs line by line, which is ideal for source code, log files, SQL scripts, Markdown, or any content where structure is not JSON.

Key features

• Side-by-side view — Original (left) and Modified (right) with removed lines highlighted in red, added lines in green. Aligned rows make it easy to match up changes.
• Unified view — Single pane with − for removals and + for additions, like classic unified diff format (diff -u).
• Live diff — Diff updates as you type in either panel; no need to click a button.
• Resizable panels — Drag the divider to give more space to the left or right editor.
• Swap sides — One-click button to swap Original and Modified without copy-pasting.
• Change counts — Shows +N added and −N removed in the diff header.
• Copy diff — Copy the unified diff output to the clipboard for pasting in tickets or code reviews.
• Download — Download the diff as a diff.txt file.
• Share — Generate a link that encodes both texts (base64 in the URL fragment). Opening the link restores left and right panels.
• Monaco Editor — Both input panels use Monaco (the VS Code engine) with syntax highlighting, line numbers, and word wrap.
• 100% client-side — Your text is not sent to any server. Processing runs entirely in the browser.

How this tool works (step-by-step)

1. Paste Original text — Put the first (e.g. old) version in the left panel. Use "Load sample" to try it with example data.
2. Paste Modified text — Put the second (e.g. new) version in the right panel.
3. View the diff — The tool computes a line diff instantly and highlights additions (green) and removals (red). Switch between Side-by-side and Unified using the toggle above the result.
4. Refine — Edit either panel and the diff updates live. Use Swap to flip sides. Drag the divider to resize panels.
5. Copy, download, or share — Use "Copy diff" to copy the unified diff to clipboard, "Download" to save as diff.txt, or "Share" to get a link.

Real-world examples with code snippets

Comparing two config files

Paste the old config in the left panel and the new config in the right. The diff highlights which lines were added, removed, or changed—useful for environment or feature-flag changes:

// Original (left)                  // Modified (right)
DATABASE_HOST=localhost             DATABASE_HOST=db.prod.internal
DATABASE_PORT=5432                  DATABASE_PORT=5432
DEBUG=true                          DEBUG=false
                                    LOG_LEVEL=warn

// Diff result:
- DATABASE_HOST=localhost           → removed
+ DATABASE_HOST=db.prod.internal    → added
- DEBUG=true                        → removed
+ DEBUG=false                       → added
+ LOG_LEVEL=warn                    → added

Comparing log outputs

Paste two log excerpts (e.g. before and after a deploy) to see which lines appeared or disappeared. This is faster than scanning hundreds of lines manually:

// Before deploy (left)              // After deploy (right)
[INFO] Starting app v2.1.0           [INFO] Starting app v2.2.0
[INFO] Connected to DB                [INFO] Connected to DB
[WARN] Cache miss rate high           [INFO] Cache warmed in 120ms
[INFO] Ready on :3000                 [INFO] Ready on :3000

// Diff shows:
- [INFO] Starting app v2.1.0
+ [INFO] Starting app v2.2.0
- [WARN] Cache miss rate high
+ [INFO] Cache warmed in 120ms

Comparing SQL queries

Paste two versions of a SQL query to see which clauses changed—useful when debugging slow queries or reviewing migrations.

Use cases

Best practices

• Normalize line endings — If one text uses CRLF (Windows) and the other LF (Unix), every line may appear changed. Normalize before comparing for a cleaner diff.
• Trim trailing whitespace — Extra spaces at the end of lines can cause false positives. Trim both texts if whitespace isn't significant.
• Use side-by-side for context — Side-by-side view is best when you need to see old and new simultaneously. Use unified view for a compact patch-style output.
• Share instead of screenshot — The Share link encodes both texts, so the recipient gets an interactive diff—not a static image.
• For structured data, use the right tool — JSON payloads are better compared with the JSON Diff tool (structure-aware). This text diff is line-based and best for plain text, code, and logs.

Common mistakes & how to avoid them

• Pasting in the wrong order — Original should go on the left and Modified on the right. If you get it backwards, click the ⇄ Swap button instead of re-pasting.
• Comparing JSON by text — Text diff shows line-level changes, so reordering keys will show as many removed/added lines even if nothing meaningful changed. Use the JSON Diff tool for JSON.
• Huge inputs slowing the browser — The diff runs client-side; very large texts (100k+ lines) may cause the tab to lag. For enormous files, use a local diff tool or split the input.
• Expecting word-level highlighting — This tool diffs at the line level. If a single character changed on a line, the entire line is marked. For character-level diffs within a line, pair with manual inspection.

FAQ

Related terms

This tool is commonly searched as text diff, compare text online, text comparison tool, side by side diff, unified diff, string diff, online diff checker, compare two files online, diff two strings, and line-by-line comparison. It helps you spot changes between any two text blobs without installing software or leaving the browser.

Similar tools

You might also find these developer tools useful:

• JSON Diff
• Text Editor
• Code Editor
• Regex Tester
• Code Minifier

Conclusion

A text diff tool makes it easy to compare two texts side by side or in unified view, with line-level add/remove highlighting, swap, resize, copy, download, and share—all in the browser with no sign-up. Use it for configs, logs, code snippets, SQL, Markdown, or any two text blobs when you need a quick, private comparison without installing software or sending data to a server.