Detect the real format of any image from its header bytes, not its file name.
File names lie. Headers do not.
Anyone can rename a file. A JPEG saved as photo.png still opens in most viewers, because viewers look at the content, not the name. But automated tools, upload validators, and archives often trust the extension, and that mismatch causes confusing errors: an upload rejected for the wrong reason, a converter that fails silently, or a collection full of mislabelled files.
This identifier reads the truth. It opens the first bytes of your file, the magic bytes that every image format writes at the start, and reports the real format. A PNG always starts with the same eight bytes. A JPEG always starts with FF D8 FF. A GIF announces itself with the letters GIF87a or GIF89a. No rename can fake that.
How to use it
Choose any image file and press identify. The tool shows the file name, the true format found in the header, what the extension claims, and a plain verdict: match, mismatch, or unknown. It also prints the first sixteen header bytes in hexadecimal, so you can see the evidence yourself.
The check happens entirely in your browser. Only the first 64 bytes are read, and nothing is uploaded anywhere. That makes the tool safe for sensitive files: a private photo or an unreleased design never leaves your device.
Formats it recognises
The tool recognises PNG, JPEG, GIF, WebP, BMP, TIFF, ICO, AVIF, HEIC, and SVG. That covers the formats you will meet in everyday work, from web images to camera files to icons. If the header matches none of them, the tool says so plainly instead of guessing. An honest unknown is more useful than a confident wrong answer.
Some formats need a second look. WebP hides its signature inside a RIFF container, so the tool checks both the RIFF marker and the WEBP marker eight bytes in. AVIF and HEIC announce themselves through their ftyp box. TIFF comes in two byte orders, little-endian and big-endian, and both are recognised. These details are why a magic-byte check beats an extension check.
Common situations
A download that will not upload to a website is often a misnamed file: a WebP saved with a .jpg extension, or a PNG saved as .jpeg by a sloppy export. Renaming the file to match its true format usually fixes the upload instantly. A folder of images from mixed sources is another case: run each file through the identifier before archiving, and your archive stays honest.
Forensic curiosity counts too. A file with no extension at all can still be identified from its header, which is handy when recovering files from old drives or chat exports. And if you ever receive a suspicious image, the header check tells you whether the file is really an image before you open it in a full editor.
What it cannot do
The identifier checks the header, not the whole file. A truncated image with a valid header will still report its format, and a corrupted middle will not be caught here. It also does not judge quality, dimensions beyond the header, or whether the image is appropriate. It answers one question, and answers it well: what format is this file, really?
Next time an upload fails or a file behaves strangely, check the header first. It takes seconds, it runs locally, and it often turns a mystery into a one-line fix.
It is also worth building the habit into any workflow that handles images from strangers. A design team receiving assets from many contributors can catch misnamed files at intake instead of discovering them during export, when deadlines are tight. A quick header check on arrival saves a frantic search later, and because this tool reads only a few bytes, checking a whole batch takes minutes rather than an afternoon.
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- Versión en español