List Intersection — Find Common Items
Find items that appear in both of two lists — the set intersection.
How it works
- 1Paste or type your text in the input field
- 2Click "Process" — processing happens in your browser
- 3Copy the result or download as a text file
What to do next
About List Intersection
List Intersection is a free, in-browser text tool. Find items that appear in both of two lists — the set intersection. The page exposes a small surface — input, controls, output — so a first-time visitor can complete the job without reading documentation.
List Intersection runs on standard browser APIs — an open-source, well-audited engine that performs the text processing natively in the browser. It accepts the formats listed in the upload area and produces output that opens in any standard text viewer. Per-run input is capped at 0 MB.
Common audiences for List Intersection include students formatting essays and researchers normalising scraped text, but plenty of people land on the page through a one-off search and never come back — that is also fine. The tool is built to be useful even when you only ever need it once.
The execution model is straightforward: your file is bytes in the tab's memory, the engine reads those bytes, computes the result, and hands the result back to the browser. The transformation happens locally, which is why the tool keeps working when your network connection drops mid-job and why it produces the same result every run for the same input.
The right moment to reach for List Intersection is when you have a focused text processing job that fits inside a browser tab. Open the page, drop in the file or paste your input, choose the options that matter, and the tool returns the result.
When the job finishes, List Intersection hands you the result as a sensibly named file. Filenames are derived from your input where possible, so a quick batch of jobs leaves you with a tidy folder rather than a pile of generic "output (3)" files. Nothing is auto-saved on Favtoo's side because nothing was ever sent there.
On limits: 0 MB per file is the ceiling. Output formats and quality settings are listed in the controls panel above, and they apply to every run.
If your task needs more than one step, chain List Intersection with Compare Two Lists, Merge Two Lists, and List Deduplicator. Each tool produces output that is a clean input to the next, so multi-step workflows are just a matter of opening the next tool in a new tab and continuing.
List Intersection is built around steady iteration on a small set of options rather than feature creep. Every additional setting attracts a slightly different audience, but a long settings panel makes the common case slower for everyone. The current controls reflect what users of the tool actually use.
List Intersection is one example of a broader pattern: utility software increasingly works as single-page, client-side experiences. Every page in the catalog is shaped that way, which keeps each tool fast to load and easy to recommend in a single link.
List Intersection runs as a regular web page, so there is no install step or permission grant before the first run. The page can be audited by viewing the source or by watching the developer-tools Network tab while a job runs.
Useful patterns when working with List Intersection: keep the input file open in another tab so you can compare against the result; give the output file a descriptive name when saving so you can find it later (the default name is sensible but generic); and treat each run as independent — the tool has no concept of "history", which means you cannot accidentally pollute one job with leftovers from another.
When something goes wrong, the cause is usually one of three things: a malformed input, a browser that is out of memory, or a corporate proxy that is interfering with the page's static assets. The first two are easy to diagnose; the third typically requires asking your IT team to allow standard browser APIs to load.
That is the whole tool. Use List Intersection for as long as it stays useful to you, and if it does, the catalog has many more tools built the same way. Each applies the same single-purpose discipline, so the way you used this page transfers to the next one you try.
How it works
- 1Land on the List Intersection page. The tool is ready to use the moment the page renders.
- 2Select the text file you want to process — drag-and-drop and the file picker both work.
- 3Adjust the options to match what you need. Sensible defaults cover the most common case, so you can usually skip this step.
- 4Click to start the job. The engine (standard browser APIs) processes the input in the page; you can watch the progress indicator until it completes.
- 5Download the result. The file is generated in your browser and saved through your normal download flow.
- 6Re-run with different settings as often as you want. Each run produces a fresh output and the original file on disk is never modified.
Common use cases
- Encode user input safely before pasting it into HTML using List Intersection.
- Re-case a title from ALL CAPS to Title Case.
- Strip messy formatting out of copy pasted from a PDF.
- Generate a slug from a long article title.
- Sort a list of items alphabetically before publishing it.
- Convert a column of names into a comma-separated list for a script.
- Reformat a JSON blob copied from a log into something readable.
- Count the words in a draft to check it fits a brief.
- Translate plain text into Markdown for a static-site post.
FAQ
How does intersection work?
It returns only items that appear in both lists (case-insensitive matching).
Are results deduplicated?
Yes — each common item appears only once in the output.
How do I separate the lists?
Use a blank line or a line with --- between the two lists.
Does order matter?
Results follow the order items appear in the first list.
Can I get the difference instead?
Use the Compare Two Lists tool to see items unique to each list.
Is my data safe?
Yes — all processing happens locally in your browser. Your text never leaves your device.
Will List Intersection keep working in a year?
List Intersection is updated whenever the underlying engine releases an improvement or a bug fix. Because the tool is delivered as a static page, every visit fetches the latest version automatically — there is no "version" to manage on your end. If a particular release ever changes default behaviour, the change is documented on Favtoo's changelog so you can confirm what shifted.
Is the source for List Intersection available?
List Intersection is a static page running an open-source engine in your browser, so a typical corporate firewall does not get in the way as long as it allows JavaScript to load from Favtoo. For teams that need to host it themselves on an internal network, the underlying engine (standard browser APIs) is open-source and can be packaged into a private build with the same behaviour. Reach out via the Contact page if that is something you are exploring.
Where does my file actually go when I use List Intersection?
Your file is processed inside your browser by standard browser APIs. The engine reads the file's bytes from your tab's memory, computes the result, and writes the result back into the tab. You can confirm what the page does by opening developer tools and watching the Network tab during a run — the requests you see are for the tool's static assets only.
Why does List Intersection feel slow on large inputs?
Most jobs finish in seconds. Speed scales with input size and with how many CPU cycles your browser tab has available — the engine runs in your browser, so it shares resources with whatever else you have open. For inputs near the 0 MB ceiling, expect anywhere from a few seconds to roughly a minute on a typical laptop. Closing other heavy tabs noticeably speeds things up.
Is List Intersection lossless?
List Intersection is built to preserve quality wherever the underlying text format allows it. Operations that are mathematically lossless (e.g. structural transformations, lossless re-encoding) round-trip with no perceptible change. Operations that involve a lossy codec inevitably introduce small artefacts at the byte level, but the defaults aim at the sweet spot where output looks or sounds the same to a normal viewer or listener while still being meaningfully smaller or faster than the input.
Can I call List Intersection from a script?
List Intersection is a browser-only tool by design and does not expose a hosted API. The reason is the same as the privacy story: there is no Favtoo backend doing the work, so there is no service to call. If you need to script the same transformation, the underlying engine (standard browser APIs) is open-source and can be used directly from your own code.
Why did List Intersection reject my input?
Failures usually fall into one of three buckets: the input is in an unsupported format, the input is over the size cap, or the input is structurally malformed (a truncated download, a partial export, or a stream the engine does not recognise). The first two are easy to confirm — check that your file is in a supported format and that it is below 0 MB. For the third, opening the file in its native viewer first is the fastest way to confirm the source is intact.