MIME Type Checker
Check MIME types by extension or inspect real files with binary magic bytes. Detect spoofed extensions, copy HTTP Content-Type headers. 100% private.
Instant MIME & Extension Lookup
Type any file extension or canonical MIME identifier for instant verification.
JavaScript Object Notation standard data interchange (RFC 8259)
Content-Type: application/json; charset=utf-8Binary Magic Byte Sniffer & True Format Validator
Drop any local file to inspect its first 32 binary bytes. Detects disguised or spoofed extensions.
Itemized Plaintext Audit Receipt
Ready-to-copy audit block documenting MIME verification and binary sniffer results.
================================================== OCTALONE MIME TYPE & BINARY AUDIT RECEIPT Generated: 2026-10-07T00:00:00.000Z (UTC) Privacy: 100% Client-Side In-Memory Execution ================================================== [SEARCH & LOOKUP DETAILS] Query: .json Resolved MIME: application/json Category: Web & Code Default Extension: .json All Extensions: .json, .map HTTP Header: Content-Type: application/json; charset=utf-8 [BINARY MAGIC BYTE SNIFFER DETAILS] No file dropped for binary sniffing. ================================================== OctalOne Developer Tools - 100% Free & Private https://octalone.com/tools/mime-type-checker ==================================================
Understanding MIME Types & Binary Magic Bytes
A MIME (Multipurpose Internet Mail Extensions) type, formally standardized by IANA as a Media Type, tells web browsers and HTTP clients how to interpret and render received byte streams. While operating systems historically relied on superficial file extensions (e.g. .jpg, .html), modern web infrastructure relies on HTTP Content-Type headers.
Why File Extensions Can Be Deceptive
A file extension is simply text appended to a file name. An attacker can rename an executable (payload.exe) or script (exploit.js) to document.pdf to bypass naive file extension upload filters on web applications.
The Power of Magic Byte Signatures
Magic numbers are constant byte sequences located at fixed offsets (usually byte 0) within a file header. For instance, authentic PNG files strictly begin with hexadecimal 89 50 4E 47 0D 0A 1A 0A. Inspecting these bytes reveals the true identity of a file.
Frequently Asked Questions
A MIME (Multipurpose Internet Mail Extensions) type, also known as a Media Type or Content-Type header, is a standardized two-part identifier (e.g. application/json, image/webp) used by web browsers, HTTP servers, and operating systems to determine how to transmit, interpret, and render a file.
File extensions (like .pdf or .png) are superficial naming conventions that can be easily renamed or spoofed. Magic bytes (or file signatures) are the actual leading binary bytes written into the file header (e.g. %PDF for PDFs or \x89PNG for PNGs). Our sniffer inspects these hardware-level magic numbers to determine the genuine format regardless of the filename.
No. All file slicing and binary header inspection execute 100% locally in your browser volatile memory using Blob.slice(0, 32) and the native HTML5 FileReader API. Zero files, binary bytes, filenames, or search queries are ever transmitted to any remote server or external telemetry service.
When you drop a file, the tool reads its first 32 binary bytes, matches the signature against our verified magic number database, and cross-references the detected type against the file's extension. If an uploaded .pdf contains PNG magic bytes (89 50 4E 47), the workstation immediately flags an amber/red spoofing security warning.
Yes! Because the engine uses native client-side zero-memory slicing (Blob.slice(0, 32)), it reads strictly the first 32 bytes of the file without loading the full file into memory. Even a 50 GB file will evaluate instantly within milliseconds without freezing your browser.