File type inspector
Identify what a file really is from its own bytes, and see the first 256 in hex.
Open this tool
Checking access…
About this tool
Drop in a file and find out what it actually is, read from the magic bytes at the start of the file rather than from its name. Around fifty formats are recognised — images, archives, PDFs, audio and video containers, fonts, databases and executables — and the tool says so plainly when a file called .jpg turns out to be something else. You also get the size, the browser’s reported media type, any byte-order mark, and a hex and ASCII dump of the opening bytes. Only the first few kilobytes are ever read, so any size of file is fine and none of it leaves your device.
Using this tool
Why does my .docx say it is a ZIP archive?
Because it is one. Word, Excel, PowerPoint, OpenDocument, EPUB and JAR files are all ZIP containers with a particular set of files inside, so they share the ZIP signature. The tool lists those extensions alongside the ZIP result rather than pretending to know which it is.
Is a mismatched extension a sign of malware?
Not on its own — renaming files is common and harmless. It is worth attention when the file came from someone you did not expect, particularly if it claims to be a document and is really an executable.
Is there a size limit?
No. Only the first four kilobytes are read, so inspecting a 20 GB disk image costs the same as inspecting a text file and uses no meaningful memory.
More files tools
Create a ZIP archive
Pack several files into one ZIP you can email or upload.
Open Create a ZIP archiveExtract a ZIP archive
Look inside a ZIP, then save just the files you actually want.
Open Extract a ZIP archiveFile checksum calculator
Compute SHA-256, SHA-1, SHA-384 and SHA-512 checksums and compare them to a published one.
Open File checksum calculatorNeed more than a quick tool?
These are free and always will be. If one of them is solving a problem you keep having, the underlying issue is usually worth a conversation.