What is Text Diff?
Text Diff is a free, browser-based tool in the Text Tools suite. Compare old and new text using a line-level LCS diff algorithm. Added lines are highlighted green, removed lines red, with line numbers for context.
The headline benefit: compare two texts line-by-line — added/removed highlighted.
Unlike most online tools that upload your file to a server, process it, and send it back, Text Diff runs entirely in your browser. Open DevTools → Network while using it and you'll see zero file-upload requests — only static assets (JavaScript, CSS, fonts) load. Your data never leaves your device.
Why use this text diff?
Three reasons EasyFileKit's Text Diff stands out from the crowd:
- **Private by design** — all processing happens locally via JavaScript and WebAssembly. No server ever sees your input.
- **Instant** — no upload wait, no queue, no server round-trip. Results appear the moment you act.
- **Free & unlimited** — no accounts, no watermarks, no daily caps. Use it as many times as you like.
How to use Text Diff — step by step
Here's the complete walkthrough. Everything happens instantly in your browser:
- **Step 1.** Paste your original text in the “Old text” box.
- **Step 2.** Paste the changed text in the “New text” box.
- **Step 3.** Read the colored table: green rows are additions, red rows are deletions.
- **Step 4.** Use the summary badges to see how many lines were added, removed or unchanged.
That's it. No sign-up, no upload bar, no waiting. If something doesn't work as expected, check the FAQ below.
Common use cases for Text Diff
People reach for Text Diff in a few recurring situations:
- When you need the result **now** and can't wait for a server-based tool to upload, queue, and process your file.
- When your file is **private or sensitive** — financial documents, personal photos, medical PDFs — and you don't want it travelling across the internet.
- When you're on a **slow or metered connection** — uploading a 50 MB file just to compress it makes no sense when the same work can happen locally.
- When you've hit the **daily limit or paywall** on another "free" tool site.
Privacy: what actually happens to your data
This is the single most important point about Text Diff, so it deserves its own section.
When you use this tool, your input is processed by JavaScript running in your browser tab. The code is downloaded once (cached afterwards) and executes locally on your CPU. At no point is your file, your text, or your input data transmitted to any server.
You can verify this yourself in under 30 seconds:
- Open Text Diff in your browser.
- Press F12 to open DevTools.
- Switch to the Network tab and tick "Disable cache".
- Use the tool — drop a file, type text, whatever the tool needs.
- Watch the Network log. You'll see only static assets (JS, CSS, fonts, icons). No request contains your data.
This isn't a setting you toggle or a promise in a privacy policy — it's how the tool is architecturally built. There is no upload endpoint to call.
Frequently asked questions about Text Diff
Q: What algorithm does this use?
A: A classic dynamic-programming Longest Common Subsequence (LCS) line diff. It produces a minimal set of additions and deletions between the two inputs.
Q: Does it compare word-by-word or character-by-character?
A: By default, line-by-line. For finer detail, run the comparison on text where each word is on its own line.
Q: What do the line numbers mean?
A: The left column is the original line number, the right column is the new line number. Equal rows show both; added rows show only the new number; removed rows show only the old.
Q: Is there a file size limit?
A: No hard limit, but very large inputs (millions of lines) can be slow because LCS is O(n·m). Most documents work instantly.
Q: Is my text sent to a server?
A: No. The diff is computed entirely in your browser — your content never leaves your device.
Text Diff: EasyFileKit vs server-based tools
Most "free" online tools that do what Text Diff does follow the same model: you upload your file to their server, they process it with a backend script, then they send the result back. Here's the honest comparison:
| | EasyFileKit | Server-based tools |
|---|---|---|
| **Your file leaves your device?** | Never | Yes, uploaded to a server |
| **Speed** | Instant (no upload) | Slower (upload + queue + download) |
| **Privacy** | Complete | Your file is on someone else's computer |
| **Cost** | Free, unlimited | Often capped or "premium" gated |
| **Works offline** | Yes (PWA) | No |
Server-based tools aren't evil — they exist because some tasks genuinely need heavy backend compute. But for everything Text Diff does, client-side processing is strictly better for you.
Under the hood: how Text Diff works
Text Diff is built with modern browser APIs. Depending on what it does, it may use:
- **Canvas API** — for image manipulation (pixel-level access, filters, resizing).
- **Web Crypto API** — native, hardware-accelerated cryptography (AES-GCM, SHA-256, PBKDF2) for any encryption or hashing.
- **pdf-lib / pdf.js** — fully client-side PDF creation and rendering.
- **MediaRecorder API** — for capturing screen, audio, and video.
- **WebAssembly** — for heavy codecs (image compression, media processing).
All of these run inside your browser's sandbox. They cannot access your filesystem (beyond files you explicitly choose), cannot make network requests with your data, and cannot run persistently in the background.
Pro tips for getting the most out of Text Diff
- **Bookmark the tool** — it works offline once cached, so you can use it even without a connection.
- **Install EasyFileKit as a PWA** — open the browser menu and choose "Install app" for a standalone window and offline access.
- **Use it on mobile** — every tool is fully responsive and works on phones and tablets, not just desktops.
- **No file size anxiety** — because nothing uploads, you can process large files that server-based tools would reject or charge for.
Try Text Diff now
The tool is right above this article — scroll up and start using it. No sign-up, no upload, no limits.
If you found Text Diff useful, explore the rest of the Text Tools suite — there are more tools that work the same private, instant, free way. And if you have a question that isn't covered in the FAQ above, the About page has our contact email.