List Diff
Compare Two Lists Online
ListDiff is a free online list diff tool to compare two lists, find differences, and run full set operations instantly. Paste one item per line on each side and get unique items in A, unique in B, the union, the intersection, and the symmetric difference, all calculated in a single pass - the fastest way to compare lists online without writing a formula or a script.
Your data stays on your device. Both lists are compared in-memory in the browser tab, and nothing — item values, counts, or even list sizes — is transmitted anywhere. Safe for email lists under GDPR, internal SKU rosters, or any line-based data you'd normally pass through a VLOOKUP. Free for personal and commercial use.
Five Set Operations, One Click
ListDiff computes every useful comparison between two lists at once. Each result is shown in its own pane, colour-coded so you can immediately identify what's unique, what's shared, and what's missing.
Set Operations Explained
Every list comparison question boils down to one of five set operations. ListDiff runs all five in parallel so you don't have to pick one upfront.
Only in A
Items that exist in List A but not in List B. The classic answer to 'what's in my old list that's missing from the new one?'
Only in B
Items that exist in List B but not in List A. The classic answer to 'what got added to the new list?'
Union
Every unique item from both lists combined, with duplicates removed. Useful for building a master list from two sources.
Intersection
Items that appear in both lists at the same time. The answer to 'which records appear on both sides?' - the core of any list reconciliation.
Symmetric Difference
Items that are in one list or the other, but not both. Symmetric difference is the opposite of intersection and reports every line that didn't match.
How To Compare Two Lists Online
Four steps to compare lists online and get every set operation at once. No formulas, no code, no sign-up.
Paste List A
Drop your first list into the List A editor, one item per line. Whitespace and blank lines are normalized automatically.
Paste List B
Paste the second list into List B. ListDiff compares the two sides and runs all five set operations in parallel as you type.
Pick Options
Toggle case sensitivity, whitespace trimming, leading-zero handling, and space normalization to match the shape of your data.
Export Or Copy
Each result pane has Copy and Download buttons. Sort alphabetically, add line numbers, or export directly as a plain text file.
Why Use ListDiff
A list comparison tool that does every set operation at once, runs entirely in the browser, and gives you export controls most spreadsheet formulas can't match.
Instant Set Operations
ListDiff computes all five set operations in parallel the moment both lists are present. No button to click, no mode to switch - every answer is always on screen.
100% Private And Secure
Your lists never leave the browser tab. Unlike list comparison tools that upload to a server, ListDiff runs entirely client-side - safe for customer emails, internal inventory, and any other sensitive data.
Every Result At Once
Only-in-A, only-in-B, union, intersection, and symmetric difference are shown side by side. No other online list diff tool gives you the full picture in a single screen.
Matching Options
Case sensitive or insensitive, trim whitespace, normalize spaces, ignore leading zeros. Tune the matching rules so 'Apple' and 'apple ' compare as equal when you need them to.
Export Controls
Copy any result to clipboard or download as a .txt file. Sort output A-Z or Z-A, prefix with line numbers, convert to upper or lower case - format the output to fit the next step in your workflow.
No Sign-Up Required
Open the page, paste two lists, get an answer. No registration, no quota, no premium tier. Free for personal and commercial use.
What You Can Compare
Any line-based dataset fits. These are the situations where ListDiff replaces a messy VLOOKUP, a one-off Python script, or an Excel add-in.
Spreadsheets And Exports
Excel, Google Sheets, and CSV exports. Copy a column, paste it into List A, paste the other column into List B, and read the five answers instantly. No formulas, no macros, no sheet gymnastics.
- Compare two Excel columns without VLOOKUP
- Reconcile CSV exports between systems
- Find rows missing from one sheet
- Cross-reference customer or SKU lists
- Audit data migrations between tools
Data And Marketing
Email lists, contact databases, and audience segments. Find overlaps, isolate new subscribers, or deduplicate a combined export before importing to a new platform.
- Deduplicate combined email lists
- Find unsubscribes between exports
- Isolate new contacts for a campaign
- Compare CRM and mailing list records
- Merge two audience segments cleanly
Development And DevOps
Package lists, feature flags, environment variables, and access control rosters. Faster than dropping into a REPL for set operations on text data.
- npm and pip package list diffs
- Feature flag audits across environments
- IAM user and group membership diffs
- Config key comparisons across deploys
- Allowed domain or IP list reviews
Compare Lists Using Python Sets
Developers often reach for Python's set operations when comparing two lists in code. The operators map directly to what ListDiff computes in the browser.
# Python: Compare two lists list_a = ['Apple', 'Banana', 'Cherry'] list_b = ['Banana', 'Cherry', 'Date'] only_a = set(list_a) - set(list_b) # Only in A only_b = set(list_b) - set(list_a) # Only in B union = set(list_a) | set(list_b) # Union intersection = set(list_a) & set(list_b) # Intersection symmetric = set(list_a) ^ set(list_b) # Symmetric diff
ListDiff gives you the same results without opening a REPL, writing a script, or installing anything. Useful when the data is in a spreadsheet or a browser tab rather than a file on disk.
Frequently Asked Questions
What is a list diff tool?
A list diff tool, also called a list comparator or list comparison tool, compares two lists and reports which items are unique to each side, which items appear in both, and various set combinations of the two. ListDiff computes five set operations at once - only in A, only in B, union, intersection, and symmetric difference.
How do I compare two lists online?
Paste one list into List A and the other into List B, with one item per line. ListDiff parses both sides, runs all five set operations in parallel, and displays each result in its own pane. Toggle case sensitivity and whitespace options in the controls above the editors.
Is ListDiff free?
Yes. ListDiff is 100% free for personal and commercial use. No sign-up, no quota, no paid tier, no watermark on any export. Every feature including sorting, copy, download, and matching options is available without restriction.
Is my data secure?
Yes. ListDiff stores both lists only in JavaScript memory for the current tab — there is no server-side database, no analytics pixel tracking the content, and no POST endpoint to collect it. When you close the tab the lists are gone. If you need proof, the Network panel in your browser's DevTools will show zero requests after the page has loaded.
How do I compare two Excel columns?
Select the column in Excel or Google Sheets, copy it, and paste directly into List A. Do the same for the second column into List B. ListDiff handles the line breaks automatically and shows the five comparisons instantly - much faster than writing a VLOOKUP or MATCH formula.
How do I find duplicates between two lists?
Use the Intersection result. It shows every item that appears in both lists at the same time - that's the set of duplicates across your two inputs. If you want to see items that appear multiple times within a single list, paste that list in both A and B.
Can I ignore case when comparing?
Yes. Uncheck Case Sensitive in the options panel to treat 'Apple', 'APPLE', and 'apple' as the same item. You can combine it with whitespace trimming, space normalization, and leading-zero stripping to handle messy real-world data.
What's the difference between Union and Symmetric Difference?
Union is every unique item from both lists combined - if something appears in either A or B or both, it's in the union. Symmetric Difference is only items that appear in one list but not the other - it excludes items that appear in both. Symmetric difference is the opposite of intersection.
How do I export the results?
Each result pane has Copy and Download buttons. Copy puts the result on your clipboard, Download saves it as a .txt file. Before exporting, you can sort A-Z or Z-A, prefix with line numbers, or convert to upper or lower case.
Can I compare lists with thousands of items?
Yes. ListDiff uses hash-based set operations, so comparison remains fast even for lists with tens of thousands of items. Practical limits come from browser memory rather than the algorithm itself.
Start Comparing Lists Online - Free
Scroll up and paste your lists. No sign-up, no downloads, no limits.