File Format Identifier & Magic Byte Checker Online
Downloaded files frequently lose their correct file extension, get renamed improperly, or fail to open due to unrecognized formats. Operating systems often guess file types solely by the extension (e.g. .jpg or .pdf), which can be misleading or corrupted. The SizeFix File Identifier reads the initial binary header bytes (known as 'Magic Bytes') of any uploaded file directly in your browser to identify its true MIME type, internal encoding, and correct extension without opening it in an external application.
Drop any unopenable, extensionless, or suspicious file into the inspection box.
View the extracted hex header, true MIME type, and detected file category.
Review the recommended extension (e.g. .pdf or .zip) and rename your file safely.
| File Format | Hex Signature (First Bytes) | ASCII Representation | MIME Type |
|---|---|---|---|
| PDF Document | 25 50 44 46 2D | %PDF- | application/pdf |
| JPEG Image | FF D8 FF E0 / E1 | ÿØÿà / ÿØÿá | image/jpeg |
| PNG Image | 89 50 4E 47 0D 0A 1A 0A | .PNG.... | image/png |
| ZIP / DOCX / XLSX | 50 4B 03 04 | PK.. | application/zip |
| WebP Image | 52 49 46 46 ... 57 45 42 50 | RIFF....WEBP | image/webp |