Free Online Text & Code Diff Checker
Compare two texts, files or snippets in milliseconds. 100% client-side privacy, side-by-side & unified views, character-level highlighting, word-level mode, syntax highlighting, and zero ads. No sign-up. No uploads. No limits.
Why teams switch
Built for people who compare things all day.
Legal editors, engineers, translators and auditors. One workspace, zero friction, no account required — ever.
Truly local privacy
Your text never leaves the tab. No server, no database, no logs — nothing to leak, nothing to subpoena.
Character-level accuracy
We don't just paint whole lines red. A second Myers pass isolates the exact characters that changed.
Side-by-side clarity
Aligned dual columns or a git-style unified patch. Toggle instantly with ⌘⇧S.
Distraction-free
No popups, no cookie walls, no paywalled "export" button. Just the diff, instantly.
How it works
Compare two texts in four steps.
Roughly eight seconds, start to finish — including the part where you read the differences.
Paste or upload
Drop the original text in the left pane. Paste raw text, upload a .txt / .json / .js / .md file, or fetch from a URL.
Add the modified version
Paste the revised document in the right pane. Comparison starts automatically as you type.
Fine-tune the comparison
Flip to Unified view, ignore whitespace/case, or switch to word-level mode to strip out noise you don't care about.
Review & export
Read the character-level highlights, then copy the summary or download an HTML report / unified patch.
Head to head
How we stack up against the top 3 diff tools.
Diffchecker, Beyond Compare and Meld are great — but each makes a trade-off. Here's the honest matrix.
| Capability | This Tool (Browser) | Diffchecker | Beyond Compare | Meld |
|---|---|---|---|---|
| Character-level highlighting | ✓ Built into every diff | ✓ Pro feature | ✓ Yes (desktop) | ✓ Yes (desktop) |
| Word-level diff mode | ✓ Toggleable | Pro only | Plugin/rule setup | Line-level default |
| Split + Unified views | ✓ 1-click toggle, both free | Split (free) · Unified (Pro) | ✓ Yes | ✓ Yes |
| Ignore whitespace / case | ✓ Instant, live filters | Limited free toggles | ✓ Advanced rules | ✓ Yes |
| Syntax highlighting | ✓ JS · JSON · YAML · HTML | Basic | ✓ Extensive | ✓ Via GtkSourceView |
| Sign-up / account required | Never | For saving/sharing | License purchase | No (open source) |
| Ads & popups | Zero | Aggressive on free | None | None |
| Privacy model | 100% in-browser | Text sent to servers | Local desktop | Local desktop |
| Free tier limits | None | 50 diffs / month (free API/account) | Trial only | Unlimited |
| Price | Free forever | $15/user/mo (Pro+) | ~$60 one-time | Free (OSS) |
| Works in browser, no install | ✓ | ✓ | ✕ Desktop only | ✕ Desktop only |
* Comparison based on publicly available pricing and feature pages as of 2026. Individual plans and capabilities may change.
Questions
Frequently asked questions
Everything about privacy, algorithms and file support.
Is my text uploaded to a server?
No — and that's not marketing. Every comparison runs inside your browser tab using JavaScript. There is no backend endpoint, no database and no analytics on your content. You can disconnect from the internet after the page loads and the tool keeps working.
What diff algorithm do you use?
We use the Myers shortest-edit-script algorithm (O(ND)) with common prefix and suffix trimming, which is the same family of algorithm used by git diff. After line alignment, a second character-level Myers pass runs on each changed line pair to isolate exactly which characters were inserted or deleted.
Which file formats can I compare?
Any plain-text format: .txt, .json, .js, .ts, .md, .csv, .xml, .html, .css, .sql, .py and more. Binary files (images, PDFs, archives) are not supported because they aren't text.
Is there a file size limit?
There is no artificial limit. Because the entire comparison happens locally, the only ceiling is your browser's available memory. Documents with tens of thousands of lines compare comfortably, and the prefix/suffix trimming pass keeps typical edits near-instant.
What's the difference between Split and Unified view?
Split view puts the original and modified text in two aligned columns so you can read them in parallel. Unified view merges both into a single column with - and + markers, exactly like a git patch — which is handy when you want to paste the result into a commit or a ticket.
Text and code diff checker for writers, developers and editors
A diff checker compares two blocks of text and shows exactly what changed between them. Instead of reading both versions line by line and hoping you notice the difference, you paste each version into a pane and the tool highlights every addition, deletion and edit in colour. It is the fastest way to answer the question every editor asks: what actually changed?
This free diff checker works for prose and for code. Switch between a side-by-side view and a unified view, choose character-level or word-level highlighting for fine-grained edits, and ignore whitespace or letter case when those differences are noise rather than signal. It is equally at home reviewing a rewritten paragraph, comparing two configuration files, or checking that a translation matches its source.
The comparison runs entirely in your browser. Drag in two files, paste two snippets, or fetch text from a URL you control, and the result appears instantly with no upload, no account and no server round-trip. Confidential contracts, unpublished copy and proprietary source code stay on your device.
A diff checker compares two versions of text or code and highlights every addition, deletion and change. ToolGuest offers side-by-side and unified views with character-level highlighting, running 100% in the browser with no upload, no account and no content tracking. It is free and private.
Why a visual diff beats reading twice
Human eyes are poor at spotting small changes across long passages. A missing comma, a flipped number or a deleted clause hides easily in a wall of text. A diff checker reduces the comparison to the differences themselves, so review time drops from minutes to seconds and nothing slips through.
Developers rely on diff output every day, but the same technique pays off far beyond code. Editors tracking a client's revisions, translators checking a revised source, lawyers comparing two contract drafts and students verifying a citation all benefit from seeing changes side by side rather than in their heads.
Options matter, because not every difference is meaningful. Indentation changes should not drown out a logic change. A switch from sentence case to title case should not hide a factual edit. Toggles for whitespace and case let you silence the noise and focus on the differences that affect meaning.
Side-by-side and unified
Pick the layout that suits the review, whether you are comparing prose or reviewing a patch.
Character and word granularity
Zoom in to single-character changes or step back to whole-word edits depending on what you need to catch.
Ignore whitespace and case
Silence formatting-only changes so genuine edits stand out instead of being buried.
Paste, drag or fetch
Drop in two files, paste two snippets, or pull text from a URL you supply, all from the same screen.
Instant, live comparison
The diff recalculates as you type, so you see the effect of an edit the moment you make it.
100% client-side privacy
Nothing is uploaded. Contracts, drafts and source code are compared locally and then discarded.
ToolGuest vs. legacy diff tools
A clean comparison without the ad clutter or the account wall.
| Capability | Legacy online tools | ToolGuest |
|---|---|---|
| Side-by-side view | Sometimes paywalled | Free |
| Unified view | Limited or missing | Included |
| Character-level highlighting | Rare | Built in |
| Ignore whitespace and case | Buried in settings | One toggle |
| File drag and drop | Upload to a server | Local read only |
| Advertising | Banners and interstitials | Zero, ever |
| Server data uploads | Text sent to servers | 100% local |
| Signup or cookies | Third-party trackers | None |
Used by teams in the USA, UK, Germany, Canada, Australia and Spain
One English page serves every Tier-1 market, so reviewers in New York, London and Berlin get the same fast, private comparison.
Legal and editorial teams compare contract drafts without sending confidential text to a third party.
Publishers check a revised article against the original to confirm only intended edits were made.
Engineering teams review configuration and code changes with whitespace noise suppressed.
Translators compare a revised source against its translation to catch drift.
Students verify that a cited quotation matches its source word for word.
Content teams compare two versions of a landing page before publishing.
Diff checker questions, answered
What does a diff checker do?
It compares two blocks of text or code and highlights every difference, marking additions, deletions and edits so you can review changes without reading both versions in full.
Does it work for code as well as prose?
Yes. The comparison is text-based, so it works for source code, configuration files, JSON, Markdown, CSV and ordinary prose equally well.
What is the difference between side-by-side and unified views?
Side-by-side shows the two versions in parallel columns, which suits prose and long lines. Unified stacks the changes in one column with insertions and deletions marked, which is the format developers see in version control.
Can it ignore whitespace and letter case?
Yes. Two toggles suppress whitespace-only and case-only differences, so a reindent or a change of capitalisation does not bury a real edit.
Is my text uploaded to a server?
No. The comparison runs entirely in your browser. Your text is never transmitted, stored or logged, and the tool works offline once loaded.
Can I compare files instead of pasting?
Yes. You can drag two files into the panes and they are read locally with the browser's FileReader API. Nothing is uploaded.
Is there a length limit?
There is no imposed limit. The practical ceiling is your browser's available memory, which comfortably handles documents far longer than most reviews.
Is the tool free?
Yes. It is completely free, needs no account and carries no ads or tracking.