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Then those files were already compressed, and that is the expected result rather than a fault. DEFLATE, the compression a ZIP uses, works by finding repetition and replacing it with references — and a JPEG, an MP4, an MP3, a PDF full of images or another ZIP has already had its repetition taken out by its own format. There is nothing left to find, so the packed size matches the original and the container's headers add a little on top. The page reports the real figure either way, including a negative saving. If the batch is all media, choose Store: it copies the files in without spending the time.

Not from a browser, and this page says so rather than half-doing it. A web page is handed a flat list of files with no paths attached — the folder each one came from is simply not part of what the browser passes on. Worse, a folder dragged onto the drop zone arrives as an object that looks like a file and then refuses to be read. Anything this page cannot read back from disk is dropped from the list and named on screen, rather than becoming an empty entry in your archive. Open the folder and select the files inside it, and they will all go in at the top level.

Dates yes, permissions no. A ZIP stores an MS-DOS timestamp whose seconds field counts in twos, so a file saved at 14:35:23 reads back 14:35:22 — that is the format's resolution and no setting improves it. The timestamp carries no timezone either, so it is written as the clock reading on your machine, which is what Finder, Explorer and unzip all expect to find. The format can only express 1980 to 2107, so anything outside that window is clamped to whichever end it fell past — 1 January 1980 or 31 December 2107 — and counted on screen by direction, because the alternative is a silent wrap that turns a 1970 date into 2098. Permissions are a different matter: a browser hands a page a name, a size, a type and a date, and no mode bits at all, so an executable script comes out of this archive without its executable bit.

No, and that is deliberate rather than unfinished. The encryption built into the original ZIP format, usually called ZipCrypto, was broken in 1994 and is recoverable given a small piece of known plaintext from any one file inside the archive, so offering it would be offering something that looks like protection and is not. The stronger AES scheme that modern archivers use is a WinZip extension the library here neither writes nor reads. If you need a protected archive, make it with 7-Zip, Keka or the archiver built into your system and choose AES-256. For sending a file rather than storing one, an encrypted transfer usually beats an encrypted container.

Normal, almost always — it is level 6, which is what the zip command and every desktop archiver default to. Measured here over 5.8 MB of source code, Normal brought the data down to 26% of its original size and Maximum reached 25.8%: six tenths of one percent, for about two and a half times the work. Fast ran in roughly half Normal's time for a result about a quarter larger, which earns its place on a very large batch. Store skips compression altogether and copies the files in, which is the honest choice for photos or video, where none of the levels finds anything. Whichever you pick, the page reports what it actually achieved.

No. Transmute processes everything locally in your browser using JavaScript and WebAssembly. Your files never leave your device — there is no server, no upload, no cloud processing.