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DevUtil

List Diff - Compare Two Lists Online

Compare Two Lists Instantly

Paste two lists into the side-by-side editors and the tool compares them in real time. Each list is split by line breaks, so every non-empty line is treated as one item. The results update as you type. There is no submit button to click and no waiting for a server response. Options for case sensitivity, whitespace trimming, and alphabetical sorting let you tailor the comparison to your exact needs.

Set Operations Explained

The tool exposes four classic set operations. Only in A (the relative complement of B in A) surfaces items exclusive to your first list. Only in B does the same for the second list. In Both returns the intersection: the items the two lists have in common. Combined produces the union: every unique item from both lists merged into one deduplicated result. Each result set shows an item count and a one-click copy button so you can drop the output straight into a spreadsheet, script, or config file.

Practical Use Cases

List comparison comes up more often than you might expect. Developers use it to spot missing environment variables when deploying to a new server, or to diff package dependency lists between branches. QA engineers compare test-case IDs from two test runs to find regressions. Marketing teams reconcile email subscriber lists after a migration. Sysadmins compare hostnames or IP addresses across firewall rules. Whenever you have two plain-text lists and need to know what changed, this tool gives you the answer in seconds.

Privacy and Performance

The entire comparison runs client-side in your browser. Your data is never uploaded, stored, or shared with any third party. The underlying algorithm uses JavaScript Set lookups, so even lists with tens of thousands of items are compared nearly instantly. Close the tab and everything is gone. There are no cookies, no local storage entries, and no analytics tied to your input.

Frequently Asked Questions

What operations does this list comparison tool perform?
The tool performs four set operations on your two lists. 'Only in A' shows items that appear in the first list but not the second. 'Only in B' shows items in the second list but not the first. 'In Both' shows the intersection, meaning items that appear in both lists. 'Combined' shows the union of both lists with duplicates removed.
How does the case-sensitivity option work?
When case-sensitive mode is on (the default), 'Apple' and 'apple' are treated as two different items. When you turn it off, those two entries are considered the same and will be deduplicated. The original casing of the first occurrence is preserved in the output.
Can I compare large lists with thousands of items?
Yes. The comparison runs entirely in your browser using JavaScript Set operations, which are very fast even for lists with tens of thousands of lines. There is no server round-trip and no upload limit.
What are common use cases for list comparison?
Developers compare environment variables, dependency lists, or database column names across environments. QA teams diff test case IDs between test runs. Marketers compare email subscriber lists or keyword lists. System administrators compare user lists, hostnames, or IP allow-lists across servers.
Is my data sent to a server?
No. All processing happens in your browser. Your lists are never transmitted over the network, stored on disk, or logged anywhere. You can verify this by opening your browser's network tab while using the tool.