File type identifier
Find out what a file really is, whatever its name says. Nothing is uploaded.
How to use it
- Add the file, several files, or a whole folder.
- Press the button. Only the start of each file is read, on your device.
- Read the list, or download it as a CSV. Files whose name does not fit their content are flagged.
Questions
How does it know what a file is?
By what is inside, not by the name. Most formats start with a fixed signature (a PNG always starts with the same eight bytes) and many have more markers further in. The tool reads the start of the file and a few other places, checks that the structure fits, and reads facts such as the size of a picture or the length of a recording.
Are my files uploaded?
No. Each file is read on your device, and only its start and a few places further in, so even a very large file is checked in a moment.
Can it tell me whether a file is safe or a virus?
No. It tells you what kind of file it is, and warns when a program has the name of a picture or a document. It does not scan for malware. Use your security software for that, and open files from people you do not know with care.
Why does it say the name does not fit?
Because the extension (the part after the last dot) is not one used for this kind of file. That happens when a file is renamed by mistake, saved in another format, or when a program is given a document’s name on purpose. Renaming a file does not convert it; to change the format, use a converter.
What does “not certain” mean?
Some kinds of file have no unmistakable signature, so the tool goes by their structure and says so. A signature that is long or specific is treated as certain, because a different kind of file is very unlikely to start the same way.
Which kinds of file does it know?
Pictures, audio, video, documents, archives, disk images, fonts, databases, programs and many more. For text it can tell text from other data and recognize things like JSON, HTML, CSV and scripts, but any text extension is accepted for text, because a text file can be named almost anything.
What about the files inside a ZIP?
A ZIP is named for what it is (a ZIP, a Word document, a Java archive and so on), but the files inside are not examined. Open it with Extract ZIP and add those files here.
Are my files uploaded anywhere?
No. This tool runs in your browser, so your files stay on your device and are never sent to a server.
Is it free?
Yes, you can use it for free. A subscription removes limits and unlocks premium tools.