Diff Checker
Compare two texts, code files or documents side by side. See added, removed and changed lines instantly, with word level highlighting inside changed lines. Runs entirely in your browser, no upload, no sign-up.
- Side-by-side and unified views
- Word level highlighting
- Ignore case and whitespace
- Copy or download as plain text
Everything runs in your browser. Nothing is uploaded. Nothing is logged.
- 100% Free
- No Sign-Up
- No Upload
- Side-by-Side View
- Word-Level Highlight
- Works Offline
Reading the diff output
Every line in the result is marked with a symbol and a colour so you can scan changes at a glance.
| Symbol | Meaning | Colour |
|---|---|---|
| + | Line added in the changed version | Emerald |
| - | Line removed from the original | Rose |
| space | Unchanged line, present in both versions | Muted |
| word bg | Only the words that differ are highlighted inside a changed line | Mixed |
Options and when to use them
Five controls, each one there to remove a specific kind of noise from the comparison.
| Option | What it does | When to use it |
|---|---|---|
| Ignore case | Treats Hello and hello as the same line | Comparing prose or non-case-sensitive configs |
| Ignore whitespace | Collapses runs of spaces and tabs before comparing | Reformatted code with different indentation |
| Hide blank lines | Removes empty unchanged lines from the output | Double-spaced drafts vs single-spaced drafts |
| Split view | Two columns: original left, changed right | Visual review, side-by-side reading |
| Unified view | One column with line numbers for both sides | Pasting into a ticket, email or diff comment |
Split view vs unified view
Two ways to read the same diff. Pick the one that matches what you are about to do with it.
| View | Columns | Shows | Best for |
|---|---|---|---|
| Split | 2 | Added, removed and changed rows aligned | Visual review |
| Unified | 1 | Plus and minus prefixed lines in reading order | Copy and paste |
Why this is the best free diff checker
Most online diff tools push your text through a server. This one never does.
| Feature | TToolDeck | Typical online diff | Desktop diff apps |
|---|---|---|---|
| Runs entirely in your browser | Yes | Partial | Yes |
| No sign-up or email | Yes | Partial | Partial |
| No file size limit from a server | Yes | No | Yes |
| Side-by-side and unified views | Yes | Yes | Yes |
| Word-level highlighting in changed lines | Yes | Partial | Yes |
| Ignore case, whitespace and blank lines | Yes | Partial | Yes |
| Live diff (no Compare button) | Yes | Partial | Yes |
| Copy and download as plain text | Yes | Partial | Yes |
| No watermark on exports | Yes | Partial | Yes |
| Works offline after first load | Yes | No | Yes |
Comparison reflects publicly available information at the time of writing. Features may change. Representative examples of common patterns.
More free developer tools
Free browser-based tools. Nothing uploaded, ever.
Diff Checker
You are hereCompare two texts or code files side by side
JSON Formatter
Format, validate and minify JSON
Base64 & URL Encoder
Encode and decode Base64 and URL strings
Password Generator
Strong random passwords generated locally
CSV Formatter
Clean and prettify CSV data
Word & Character Counter
Words, characters and reading time
Case Converter
UPPERCASE, lowercase, Title Case, camelCase
QR Code Generator
QR codes for URLs, WiFi and WhatsApp
How it works
- 1
Paste both versions
Drop the original text into the left panel and the changed text into the right panel. The diff appears instantly, no button to press.
- 2
Tune the comparison
Toggle ignore case, ignore whitespace or hide blank lines to remove noise. Switch between split and unified views to match your workflow.
- 3
Read, copy or download
Scan the highlighted diff, then copy the unified output to your clipboard or download it as a plain text file with plus and minus prefixes.
Everything you get for free
Side-by-side and unified views
Switch between a two-column split view for visual comparison and a unified stream that reads like a classic git diff.
Line and word level highlighting
Changed lines get a rose or emerald background. Within changed lines, only the words that actually differ are highlighted.
Ignore case, whitespace and blank lines
Focus on real content changes. Turn off noise from trailing spaces, casing differences or empty lines.
Live diff as you type
No Compare button needed. Paste both versions and the diff updates instantly with counts of added, removed and unchanged lines.
Copy and download as plain text
Export a unified diff with + and minus prefixes for pasting into a ticket, an email or a review comment.
Handles large files
Built on an efficient longest common subsequence algorithm with a safety cap so the page never locks up on huge inputs.
Zero upload, zero tracking of contents
Your text never leaves your device. There is no server side diff, no logging of your content, no analytics on the text itself.
Works on mobile
Split view stacks cleanly on small screens so you can compare snippets from your phone or tablet without pinching.
What people use it for
Reviewing code changes
Compare a file before and after an edit to spot a missing brace, a renamed variable or a lost line before you commit.
Checking contract or policy edits
Paste an old and new version of a document to see exactly which sentences were added, removed or reworded.
Debugging config files
Compare two environment files, JSON configs or YAML blocks to find the one line that differs between working and broken.
Proofreading revisions
Authors and editors can diff two drafts to confirm every requested change landed and nothing was lost in the edit.
Comparing translations
Line up source and translated text to verify that no strings were dropped or duplicated between languages.
Verifying data exports
Diff two CSV exports or SQL dumps to confirm a migration produced the expected rows and no data was silently lost.
Questions people ask
Is the diff checker really free?
Yes. The tool is free to use with no sign-up, no watermark and no export limit. ToolDeck may show ads to pay for hosting.
Are my files or text uploaded to a server?
No. The comparison runs entirely in your browser using JavaScript. Your text never leaves your device. You can verify this by opening your browser network tab and watching that no request carries your content.
Is there a file size limit?
There is no server side limit because nothing is uploaded. The practical limit is your device memory. Very large inputs are handled with a safety cap so the page stays responsive.
Can I compare code files?
Yes. The tool is plain text, so any code, JSON, YAML, Markdown, SQL or config file works. Paste the contents of each file into the panels.
What does ignore whitespace do?
It collapses runs of spaces, tabs and newlines to a single space before comparing, so indentation changes are not flagged as differences. Useful when reformatting code with a different indent style.
What does ignore case do?
It lowercases both sides before comparison, so Hello and hello count as the same line. Useful for prose, config keys and user content where casing does not matter.
How does the word level highlighting work?
When a line is marked as changed, the tool runs a second diff on the words inside that line and highlights only the words that actually differ. This makes small edits easy to spot inside otherwise identical lines.
Can I download the diff?
Yes. The Download button saves a unified diff as a plain text file with plus and minus prefixes, ready to paste into a ticket, a code review or an email.
Which browsers are supported?
Current versions of Chrome, Edge, Firefox and Safari, on desktop and mobile. Everything uses standard web APIs and no browser specific features.
Does it work offline?
After the page first loads, the diff checker keeps working without an internet connection because everything runs locally. There is no server round trip on any comparison.
Is there a limit on the number of comparisons?
No. You can compare as many times as you like. There is no daily quota, no account and no rate limit.
Do you keep logs of my text?
No. There is no server side component and no logging of your content. The only thing that ever leaves your browser is an anonymous page view, if you have analytics consent enabled.
Your text never leaves your browser
The entire comparison runs in JavaScript on your device. There is no server side diff, no logging of your content and no analytics on the text itself. You can verify this by opening your browser network tab while comparing. Read how we keep it private.