File MIME Type Checker
Drop any file to see its true MIME type — as declared and as sniffed from magic bytes — plus size and details.
About This Tool & Technical Logic
File extensions lie: rename malware.exe to invoice.pdf and the extension says PDF. The MIME type a browser actually trusts comes from magic bytes — the signature header at the start of the file (e.g., %PDF for PDFs, ‰PNG for PNG).
This checker reads the first bytes locally and identifies the real format, comparing it against the extension's declared type. A mismatch is exactly how disguised files are caught — and how misconfigured upload servers get abused.
FileReader → first 16 bytes → magic-byte signature table (PDF, PNG, JPG, GIF, ZIP, RAR, 7z, EXE, MP4, MP3, WEBP, SVG, WOFF…).
How to Use — Step by Step
- 1
Drop the file
The file never leaves your machine — bytes are read in-browser for signature matching.
- 2
Compare declared vs detected
Green = extension and content agree. A red mismatch means the file isn't what it claims — scan it before opening.
- 3
Use the details
Exact MIME string, signature hex, and size — handy for upload validators configuring their accept lists.
Frequently Asked Questions
Fixed byte sequences at a file's start that identify its true format — %PDF (25 50 44 46), ‰PNG (89 50 4E 47), MZ for Windows executables.