Spot a file whose extension lies, such as an .exe renamed to .pdf or a .zip named .jpg
Processed in your browser. Nothing is uploaded. Updated on 24 Oct 2026.Renaming invoice.exe to invoice.pdf changes nothing inside it, and attachments that pretend to be documents are one of the oldest tricks for getting someone to run a program. Drop the file here: its first bytes are read on your device and matched against the signature of the format it claims to be. If a so-called PDF opens with the bytes of a Windows program or a zip archive, the page says so in one line at the top.
Press Select a file and pick the attachment or download you do not trust.
Its first bytes are matched against the signature of the format its extension claims.
If the name lies, a warning under the top line says what the file really is, such as a program named .pdf.
Do not open a file whose bytes disagree with its name; delete it or ask the sender.
The File Analyzer exists because a site with a hundred and forty tools and no way in is harder to use than one with ten. Rather than asking you to guess which tool you want, it asks for the file and works backwards from it.
What it establishes, and how. The name and the extension come from your device. The format comes from the file's own opening bytes, matched against the signature table every format on this site is described by, which is why a JPEG named photo.png is reported as a JPEG. The MIME type follows from that verdict, with your browser's own claim shown beside it whenever the two disagree. The size is given both as a human figure and as an exact byte count, because upload portals count bytes. The magic number is printed in hex and as characters, with the offset it sits at. Dimensions are read out of the header for PNG, JPEG, GIF, BMP, WebP, TIFF, ICO, SVG, HEIC and AVIF, without ever decoding the picture, so a forty-megapixel photo is measured instantly. Metadata means EXIF, XMP, IPTC and embedded text, including the GPS position a phone writes into a photo. The hashes are SHA-256 and MD5, computed over every byte.
Nothing is uploaded. The first 64 KB are read to recognise the file, the last few to see whether a PDF is locked, and the hash is taken in four-megabyte slices so a multi-gigabyte file never has to sit in memory at once.
The rest of the article, and all 8 questions about File Analyzer, are on the File Analyzer page.
Drop the file on this page. Almost every binary format writes a fixed run of bytes at its start, so a PNG, a PDF, a zip or an MP4 is recognised from its contents whatever the file happens to be called. The verdict, the signature bytes behind it and the offset they sit at are all shown.
Renaming a file changes its label and nothing else. A photo saved as JPEG and later renamed to .png is still a JPEG inside, and any portal that checks properly will reject it. The analyzer reads the bytes, says which format they really are, and offers the converter that would make the name true.
No. The first 64 KB are read in your own browser to recognise the format and measure the picture, the last 4 KB to see whether a PDF is locked, and the hash is computed slice by slice on your device. Nothing reaches a server, so there is nothing for anyone to delete afterwards.
Those bytes are how software recognises a format without trusting the filename. A PNG begins 89 50 4E 47, a PDF begins %PDF, a zip begins PK. Seeing them in hex proves what the file is, which matters when an upload keeps failing or when a download does not open in the program it should.
Still stuck? Ask about File Analyzer and anybody who knows can answer. No account needed.
Same job, other tools: HEIC to PDF – Convert iPhone HEIC photos straight into a PDF · JPG to PDF – Convert JPG photos into a single PDF, in the order you choose · Compress PDF to 500 KB – Fit a multi-page scan under 500 KB with its text still readable · Compress PDF to 50 KB – Get a one-page scan under 50 KB for strict document uploads.
On the related tools: HAR Sanitizer – Remove cookies, Authorization headers and tokens from a HAR before sending it to support.
In the collection File Converter.