File MIME Detector
Drop any files to learn what they really contain. Instead of trusting the extension, the detector reads each file’s first bytes, the signature or “magic number” most formats start with, and identifies over 70 formats, including Word, Excel and PowerPoint files inside their ZIP containers. It shows the real MIME type, compares it with the name, and warns about mismatches and programs disguised as documents.
- Runs in your browser
- No sign-up
- Free to use
| File | Detected format | MIME type | Name says | Verdict |
|---|
How to use File MIME Detector
- Drop one or more files of any type.
- Read the detected format and MIME type.
- Check the verdict for mismatches and programs.
- Download the results as CSV if needed.
File MIME Detector features
Signature detection
Images, documents, archives, audio, video, fonts, databases and programs.
Inside containers
Tells DOCX, XLSX, PPTX, ODF, EPUB, JAR and APK apart from plain ZIP.
Text sniffing
Recognises HTML, SVG, XML, JSON, CSV, PEM keys and scripts.
Mismatch alerts
Compares content with the extension and the browser’s guess.
Executable warning
Flags Windows, Linux and macOS programs whatever their name.
Any size, private
Reads only the first 256 KB of each file on your device.
When to use File MIME Detector
- Identifying a file that arrived without an extension.
- Checking an attachment before opening it.
- Verifying uploads in a support ticket or data pipeline.
- Finding files with wrong extensions in a download folder.
File MIME Detector FAQ
How can the type be known without the extension?
Most formats begin with a fixed sequence of bytes, such as %PDF for PDF or 89 50 4E 47 for PNG. Reading those bytes identifies the format regardless of the name.
Why does the browser report a different type?
Browsers guess the MIME type from the extension, not the content. The detector shows both so you can see when they disagree.
Can it tell a DOCX from a ZIP?
Yes. Office and OpenDocument files are ZIP archives; the detector looks at the names inside to tell Word, Excel, PowerPoint, ODF, EPUB, JAR and APK files apart.
Is a “Program” verdict dangerous?
It means the file can run code, such as a Windows .exe. That is normal for installers you trust, but a program named like a document is a common malware trick.
What about plain text files?
Text has no signature, so it is identified by its content: HTML, SVG, XML, JSON, CSV, PEM keys and scripts are recognised, the rest is plain text.
Are my files uploaded?
No. Only the first bytes are read, in your browser.
Identifying files by their content
A file’s name is easy to change; its content is not. That is why systems that need to know what a file really is, from antivirus scanners to the Unix file command, look at the bytes at the start of the file. Most binary formats begin with a fixed signature, sometimes called a magic number, chosen precisely so that the format can be recognised.
The detector reads up to the first 256 kilobytes of each file and compares them with signatures for more than seventy formats: PDF, the common image formats including WebP, AVIF and HEIC, audio and video containers, archives such as ZIP, 7z, RAR, GZIP and TAR, fonts, SQLite databases, WebAssembly, and executable programs for Windows, Linux and macOS.
Some formats share a container. Word, Excel and PowerPoint files, OpenDocument files, EPUB books, Java archives and Android apps are all ZIP archives inside. The detector walks the archive’s first entries to see which characteristic files it contains and names the real format. ISO media files such as MP4, MOV, HEIC and AVIF are told apart by the brand in their header.
Text-based formats have no signature, so their content is examined instead: HTML and SVG markup, XML declarations, JSON that parses, delimited lines that look like CSV, PEM-encoded keys and certificates, and scripts that begin with an interpreter line. Anything else is reported as plain text or, for unrecognised binary data, as unknown.
The result is compared with the file’s extension and with the MIME type the browser derived from that extension. Matches are confirmed, mismatches explained, and programs flagged, especially when their names suggest documents. Upload handlers on websites should perform the same check on the server; this tool lets you do it by hand for any file without uploading it.