Identify a File's Real Format From Its Binary Signature
Check what a file actually is, regardless of what its extension claims, and spot mislabelled images.
About the Image Format Detector
File extensions are a naming convention, not a fact. Renaming a photograph to end in .jpg does not make it a JPEG, and a great many upload failures come down to a file whose contents do not match its name. This tool ignores the name entirely and reads the opening bytes, where every image format leaves a distinctive signature, then reports what it genuinely found.
Twelve formats are recognised: PNG, JPEG, GIF, WebP, BMP, TIFF, ICO, AVIF, HEIC, SVG, PDF and PSD. Alongside the detected format the table shows a verdict comparing it against the extension on the filename, flagging clearly when the two disagree. Several files can be checked at once, which turns a folder of suspect uploads into a single readable list. Nothing is converted or downloaded — this reports and stops — and the inspection is done in the page.
Key Features
- Twelve formats recognised: Covers the common web and camera formats plus PDF and Photoshop documents.
- Extension cross-check: Each row states whether the filename agrees with the real contents, so mismatches stand out immediately.
- Several files at once: Check a whole batch and read the results as one table rather than testing files individually.
- Only the header is read: Just the first part of each file is examined, so even very large files are identified almost instantly.
- Purely diagnostic: Nothing is altered or produced; the tool answers the question and leaves the files alone.
How to Use the Image Format Detector
- Add the files you are unsure about — any file type is accepted.
- Run the detection.
- Read the table: the detected format sits beside a check on whether the extension agrees.
- Convert any mismatched file to the format you actually need.
How It Works
Only the first 512 bytes of each file are read, and that slice is tested against a list of known signatures — the byte pattern that opens a PNG, the marker that begins a JPEG, the container tags that identify AVIF and HEIC, and so on. SVG is detected differently, by looking for its opening tag in the leading text, since it is a text format rather than a binary one. The detected format is then compared with the filename's extension, treating the usual equivalents as matching so a .jpeg is not wrongly reported against a JPEG. Because only the header is inspected, the tool confirms what a file claims to be structurally; it does not verify that the remainder of the file is complete or undamaged.
When You Need It
A helpdesk technician is handed a ticket saying a form keeps rejecting a customer's photograph even though it is definitely a JPG. Running the file through the detector shows it is actually a HEIC straight from an iPhone that someone renamed, which explains the rejection instantly and turns a long back-and-forth into a one-line answer. The attachment is a customer's identity document, so diagnosing it through a public analysis site would be the wrong way to close a ticket quickly. Developers debugging upload validation and archivists auditing an inherited folder of files check formats the same way.