Create a ZIP in the Browser: What Ends Up Inside files.zip

I work on OnePassApps, the team behind the browser-local studios at app.onepassapps.com. One File Studio tab packs the files you drop on the stage into a ZIP archive, and the interesting part is what actually ends up inside that archive.

What you drop on the stage

Any files - the tab says "Any files · up to 500 and 256 MiB in total · stays on this device". Each file appears on the stage with its size and a status, so you can see what was picked up before anything is built. The options block shows the limits as you go: "Files 0 of 500" and "Total size 0 B of 256 MiB".

The options block also states the rule for two files that share a name: "Duplicate names - Numbered, e.g. “notes (2).txt”". That rule matters more than it sounds, and I tested it rather than assuming it.

What comes out

One archive, always called files.zip. The panel puts it plainly: "Create ZIP builds files.zip from the list on the stage. Your originals stay unchanged."

I ran it on five files: a 1.2 KiB text file, a 55 B CSV, an 82 B JSON file, and two files both called notes.txt coming from two different folders. The result panel answered "Created one ZIP with 5 files (816 B)" and "5 files · 816 B · 42% smaller", and offered "Download files.zip". The run took 0.4 s.

The 42% is real. The five source files add up to 1,396 bytes and the archive on disk is 816 bytes. It is an ordinary ZIP: the first four bytes are the PK signature, and unzip on the command line reads it without a complaint - "No errors detected in compressed data of files.zip." The listing inside the archive matches what the stage showed:

So the duplicate was renamed rather than overwritten: notes.txt kept the copy from the first folder and notes (2).txt holds the copy from the second, and unzip -p on each one prints its own text. The entries are deflated, and each one carries the timestamp of the file it came from.

The edge worth knowing

The percentage is about the archive as a whole, not about every file in it. In my test the 20-byte notes.txt actually grew slightly inside the ZIP, and the 55-byte CSV shrank to 46 bytes. What you get is the sum of those entries plus the ZIP headers - so if your files are already compressed, the archive can come out no smaller than the files you put in. Read the number on the result card rather than assuming a win.

Where it runs

Processing stays in this browser. The files are read in the tab, packed in the tab and exported from the tab, so nothing is uploaded to a server to do the work. The panel says it plainly: "Nothing leaves this tab."

You can try it here: app.onepassapps.com/studios/files. The other studios are listed on the guides page.

One membership covers all seven studios, and Standard is free right now: $0 a month, 100,000 credits every 30 days, no card required. The studios themselves need no account and use no credits.

I work on OnePassApps, so you know where this comes from. The guides page has the rest of the tools.