🧬 文件真实格式识别（文件头）File Type Detector (Magic Bytes)
根据文件开头的特征字节（Magic Number）识别文件的真实格式，不看扩展名，能发现改了后缀的文件；同时附有 80 多种常见文件头对照表。Identify a file’s real format from its leading signature bytes (magic number) instead of its extension, catching renamed files — with a reference table of 80+ common signatures.
常见文件头对照表Common file signatures
使用说明与常见问题How-to & FAQ
「文件真实格式识别（文件头）」是什么？What is the File Type Detector (Magic Bytes) tool?
根据文件开头的特征字节（Magic Number）识别文件的真实格式，不看扩展名，能发现改了后缀的文件；同时附有 80 多种常见文件头对照表。Identify a file’s real format from its leading signature bytes (magic number) instead of its extension, catching renamed files — with a reference table of 80+ common signatures.
如何使用「文件真实格式识别（文件头）」？How do I use the File Type Detector (Magic Bytes)?
选择或拖放一个或多个文件，工具只读取文件开头的少量字节，显示识别出的格式、对应扩展名和 MIME 类型，并提示扩展名是否与真实格式不符。下方表格可以搜索各种格式的文件头。Pick or drop one or more files; only the first bytes are read. You get the detected format, the matching extension and MIME type, and a warning when the extension does not match. Search the signature table below for any format.
为什么改了扩展名还能识别出来？How can it tell when the extension was changed?
扩展名只是文件名的一部分，可以随意修改；而大多数格式在文件开头都有固定的特征字节（例如 PDF 以 %PDF 开头，PNG 以 89 50 4E 47 开头），这些字节不会因为改名而变化。The extension is just part of the name and can be changed freely, but most formats start with fixed signature bytes (PDF starts with %PDF, PNG with 89 50 4E 47) that renaming does not touch.
docx、xlsx 为什么显示为 ZIP？Why do docx and xlsx show up as ZIP?
Office 2007 以后的文档、JAR、APK、EPUB 本质上都是 ZIP 压缩包。工具会进一步查看压缩包内的文件名（如 word/、xl/、AndroidManifest.xml）来区分具体类型。Modern Office files, JAR, APK and EPUB are all ZIP archives inside. The tool looks at the file names in the archive (word/, xl/, AndroidManifest.xml…) to tell them apart.
「文件真实格式识别（文件头）」免费吗？数据会上传吗？Is the File Type Detector (Magic Bytes) free? Is my data uploaded?
「文件真实格式识别（文件头）」完全免费，无需注册或安装，手机和电脑都能用；所有处理都在你的浏览器本地完成，输入的内容和文件不会上传到服务器。The File Type Detector (Magic Bytes) is completely free with no sign-up or install and works on phones and desktops; everything runs locally in your browser and nothing you enter is uploaded.