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Developer tool
Check a file's real MIME type online by comparing the browser type, file extension, and magic-byte signature. Free and private — files never leave your browser
MIME Type Detector on ToolBesty is a free online MIME type checker that tells you what a file really is. Pick a file and it reports three results side by side: the MIME type your browser assigns, the type implied by the file extension, and the type detected from the file's magic bytes. Detection runs in your browser by reading the first bytes of the file, so nothing is uploaded.
File extensions are easy to rename, and browsers often guess a MIME type from the name alone. Real MIME type detection looks at the file signature, the fixed bytes at the start of many formats. Comparing all three results shows at once when a file named photo.png is actually a JPEG, or when an upload has no extension at all.
This MIME tool recognises the signatures for PDF, PNG, JPEG, GIF, RIFF containers (WebP images or WAV audio), ZIP archives (which also covers DOCX, XLSX, and EPUB), and MP3 files with an ID3 tag. The extension lookup covers common types including PDF, PNG, JPG, GIF, WebP, SVG, MP3, WAV, MP4, JSON, ZIP, TXT, CSV, HTML, CSS, and JS. Anything outside those lists is reported as unknown.
If you found this page while searching for mime-detective, the JavaScript library that identifies files by their signatures, this gives you a quick no-code check in the browser. It is handy for debugging upload validation, checking a suspicious download, or confirming the Content-Type you should send.
ToolBesty is operated by Vishvajeet Shukla. For privacy details on browser tools, accounts, and AI features, read our Privacy Policy.
Click the file picker and select any file from your device. The file name and size appear first.
Read the browser type, the type from the extension, and the type from the magic bytes.
If the extension and magic bytes disagree, rename the file, re-export it, or reject it in your upload flow.
See exactly what a browser reports as the file type versus what the bytes say when a server rejects a valid upload.
Catch images, PDFs, or archives whose extension was changed and no longer matches the real format.
Confirm the right MIME type before serving a file from storage or a CDN.
Tip: after you finish, check Related tools at the bottom of this page for the next step in your workflow.
Quick answers about tools, privacy, limits, and pricing.
Many formats start with a fixed signature, such as %PDF for PDF or the PNG header bytes. The tool reads the first 16 bytes of your file and matches them against known signatures.
PDF, PNG, JPEG, GIF, RIFF files (WebP or WAV), ZIP-based files (ZIP, DOCX, XLSX, EPUB), and MP3 files that begin with an ID3 tag. Other formats show as unknown.
Browsers infer the type from the extension. If the extension is missing or unfamiliar, the browser leaves the type blank, which is when the magic byte check helps most.
DOCX, XLSX, and EPUB are ZIP archives internally and share the same starting bytes, so the result is shown as ZIP with those formats noted as possibilities.
No. This online MIME type checker reads the file locally in your browser. Only the first bytes are inspected, and the file never leaves your device.
Yes. MIME Type Detector is free to use on ToolBesty. Guests and free accounts may have daily limits on some tools; premium tiers can raise or remove those limits. AI tools may also spend credits.
For browser-based tools, processing runs on your device when possible and files are not uploaded for conversion. Optional accounts, usage limits, and AI features are described in our Privacy Policy.
No for most tools — you can start as a guest. An account helps keep higher daily limits and saved work (for example AI resumes).
Close other heavy tabs, use a smaller input file, and try Chrome or Edge on desktop. Very large files can stress browser memory.
Yes, the page is responsive. Complex media or large PDFs still work better on desktop because of memory and CPU limits on phones.
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