File extensions lie. An image saved as photo.jpg might really be a PNG, and a .png might secretly be a WebP — mismatches that cause upload errors, broken editors and security problems. The Image Format Detector reads a file’s magic bytes, the first few bytes that every image format uses as a fingerprint, and tells you the true format. Paste hex, or upload a small file and the tool reads the first bytes for you.
What Are Magic Bytes?
Every binary image format starts with a distinctive signature. A JPEG always begins with ffd8ff, a PNG with 89504e47, a GIF with the ASCII letters “GIF”, and a BMP with “BM”. These signatures are far more reliable than file extensions, which anyone can change. By checking the first few bytes, the detector identifies the actual encoding regardless of what the filename claims — and can also spot truncated or corrupted files whose signatures are missing or wrong.
How to Use the Detector
- Paste the file’s magic bytes as hex (the first 8-16 bytes work for almost every format).
- Or click Upload a Small File and the tool reads the first 16 bytes for you.
- Click Detect Format.
- Review the detected format, MIME type and common file extensions.
- Read the insights for guidance on the format and when to use it.
Key Features
- Seven formats: JPEG, PNG, GIF, WebP, AVIF, BMP and SVG.
- Magic-byte matching: detects by signature, not extension.
- Upload or paste: read bytes from a file or analyze hex directly.
- Confidence score: see how certain the detection is.
- MIME and extensions: complete technical details for developers.
Why Detecting the True Format Matters
Mislabeled image files cause real problems. Web servers rely on the correct Content-Type header to render images, and many upload validators reject files whose header does not match their extension. Security reviewers check magic bytes to make sure an “image” is not actually a script or an executable with a renamed extension. Developers debugging broken image displays use magic bytes to confirm what the server actually received. And when a batch of files arrives with no extensions at all, format detection identifies every one in seconds.
Tips for Working with Magic Bytes
- Read from the start. The signature is always in the first bytes — you rarely need more than 12.
- Hex may include spaces. The tool ignores spaces and 0x prefixes, so paste freely.
- SVG is text. It has no binary signature, so detection looks for the opening markup like <svg.
Frequently Asked Questions
What if the tool says “unknown signature”?
The bytes do not match any supported format. The file may be corrupted, truncated, a different format, or simply not an image.
Can it detect a file with the wrong extension?
Yes — that is exactly what magic-byte detection is for. If photo.jpg actually contains PNG bytes, the tool reports PNG.
Is my file uploaded anywhere?
No. Only the first few bytes are read, and everything is processed locally in your browser.
Conclusion
Knowing a file’s true format beats trusting its name. Use the Image Format Detector to verify uploads, fix mislabeled files and debug display errors — quick, private and accurate.