A file you cannot open is usually one made by a program you do not have: an Outlook mailbox, an Access database, an AutoCAD drawing, a Pages document from a Mac, a scan from a hospital. The tools on this site open many of those in the browser, without the program and without uploading the file. This page finds the right one, and it goes by what is inside the file rather than trusting its name, because an extension is only a label and the labels on files people send are often wrong.
Some kinds of file it shows right here, such as contacts in a .vcf. For any other file it names the tool that opens it, and if nothing here does, it still shows you the file's real type and its text or first bytes, which is often enough to tell what a mystery file is.
When nothing here opens a file, or a type you type in has no tool, the page tells this site that type's extension - only that, and for a file that is not text its first 8 bytes, the signature that says which format it is - so the types people need most can be added next. Never the file, its name or what is in it.
- Is my file uploaded when I drop it here?
- No. The file is opened by your browser, on your computer, and nothing in it is sent anywhere. To recognise it the page reads only its first 64 KB; it reads the rest only when it is showing you the file. The tool you go on to says above its title where it does its work, and nearly all of them work entirely in your browser.
- Why do I have to choose the file again in the tool?
- Each tool opens files itself, and a file you choose in one page cannot be handed to another without being chosen again. The page names the tool, and you pick the same file there.
- The page says my file is really something else. Why?
- Most file formats begin with a fixed signature, a few bytes that say what they are, so a PDF saved as attachment.dat still starts like a PDF. When the name and the contents disagree, this page believes the contents and sends you to the tool for what the file really is.
- How do I see a file's extension?
- Windows hides them by default: in File Explorer, open View, then Show, and tick File name extensions. On a Mac, open Finder, then Settings, then Advanced, and tick Show all filename extensions.
- What if nothing here opens my file?
- Use the link that appears to say what the file is and where it came from. File types people cannot open are exactly what new tools here are chosen from.
- Can I open these files with a double-click?
- Yes, in Chrome or Edge: choose Install as an app at the bottom of any page (or the install icon in the address bar). The site then appears in your computer's Open with menu for the file types nothing else opens - DWG, MPP, CorelDRAW, SketchUp, Visio, Publisher, PST, OneNote, EMF, DAV, SPSS and about forty more - and can be made their default app. The file still never leaves your computer: the installed app is this same website, reading the file in the window it opens. PDFs, photos, videos and Office documents are left to the programs you already have.