What this site is
krun.ch is a plain-language reference about file compression. It explains what archives are, how the common formats differ, and how to open or create them on everyday devices – without the jargon that usually surrounds the topic.
The aim is narrow on purpose. Rather than cover every tool and edge case, the guides focus on the questions people actually ask: why a file did not shrink, which format to send, how to extract something on a phone. Each one is written to be read once and understood, then closed.
What you will find here
The site is built around a short set of guides and a few practical tools. The guides explain how compression works, compare the common formats, walk through opening an archive on any device, and weigh online tools against desktop ones. None of them assumes prior knowledge, and each can be read on its own. Alongside them sit a handful of in-browser tools – for zipping files, opening a .zip, measuring how much a file would shrink, and checking that a download arrived intact. Together they cover the everyday situations most people meet: receiving an archive, sending one, or wondering whether compressing something is even worth the effort.
Tools that stay on your device
The tools here were built on a single principle: your files should never have to leave your computer to be useful. Each one runs entirely inside the browser, using a compression feature built into modern browsers themselves, so nothing is uploaded and no account is needed. That makes them safe to use even with private documents, and it is why the site can offer them free, without the storage and bandwidth costs that force most online services to cap file sizes or hold your data on a server.
How the guides are written
Every guide sticks to behaviour that holds across tools and versions, so the advice stays accurate as software changes. Where a step depends on the operating system, the relevant platforms are spelled out. Format names such as ZIP, RAR and 7z refer to the formats themselves, not to any single product, and remain the trademarks of their respective owners.
Who writes this
Get in touch
Spotted something that has dated, or a question the guides do not answer? Suggestions are welcome and help keep the references clear and current.
Frequently asked questions
Does krun.ch recommend one particular program?
No. The guides deliberately focus on formats and methods that work across tools, rather than promoting any single product. Where a free tool is genuinely needed for a less common format, it is mentioned as an example, not an endorsement.
Can I quote or link to these guides?
Short quotations with a link back are welcome, and links to any page are always fine. The guides aim to be a stable reference worth pointing people to.
How do I report an error or suggest a topic?
Corrections and suggestions are genuinely useful. If a step has dated or a common question is missing, get in touch so the reference can be kept accurate.