MIME type checker online: identify any file's MIME type free

Upload a file or enter a file extension to identify its MIME type, ToolHQ's MIME type checker uses the IANA registry. Your file is checked locally in your browser, no content is sent anywhere.

A MIME type (Multipurpose Internet Mail Extensions type) is a standardized label that tells software what kind of data a file contains. Every file has a MIME type, and correct MIME types matter when serving files over the web, handling file uploads in applications, configuring email attachments, and setting API response headers.

When a web server sends a file to a browser, it includes a Content-Type header with the MIME type. If that header says text/html, the browser renders the response as a web page. If it says application/pdf, the browser opens the PDF viewer. If it is wrong, the user sees garbled content or an unexpected download prompt.

Key takeaways

• MIME types follow the format type/subtype (e.g., image/jpeg, text/html)
• ToolHQ identifies MIME types by file upload (reads actual content) or by file extension
• Your file is checked locally in your browser, no content is sent anywhere
• The IANA maintains the official registry of registered MIME types
• Correct MIME types are required for correct browser behavior and API responses

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What MIME types are and where they come from

MIME was originally defined for email to describe the type and encoding of message parts. RFC 2046 defines the MIME content type structure. The IANA (Internet Assigned Numbers Authority) maintains the official registry of registered MIME types, updated continuously as new formats are standardized.

A MIME type has two parts separated by a slash: type/subtype. The type is a broad category (text, image, video, audio, application) and the subtype is the specific format within that category (html, jpeg, mp4, mpeg, json).

Some examples:

• text/html, HTML web page
• image/jpeg, JPEG image
• application/json, JSON data
• video/mp4, MP4 video
• application/octet-stream, generic binary data (used when no specific type is known)

The x- prefix convention (like application/x-www-form-urlencoded) was used for unofficial types. The IANA now discourages new x- types, preferring vendor-specific types in the vnd. namespace or registration of new official subtypes.

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15 common MIME types reference

MIME type	File extension	Description
text/html	.html, .htm	HTML web pages
text/css	.css	CSS stylesheets
text/javascript	.js	JavaScript files
text/plain	.txt	Plain text
application/json	.json	JSON data
application/xml	.xml	XML data
application/pdf	.pdf	PDF documents
application/zip	.zip	ZIP archives
application/octet-stream	(any binary)	Unknown binary data
image/jpeg	.jpg, .jpeg	JPEG images
image/png	.png	PNG images
image/webp	.webp	WebP images
image/svg+xml	.svg	SVG vector graphics
video/mp4	.mp4	MP4 video
audio/mpeg	.mp3	MP3 audio

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Extension-based vs. content-based detection

MIME types can be identified two ways, and they can disagree.

Extension-based detection looks at the file extension (.jpg, .pdf, .json) and returns the MIME type associated with that extension in the system's MIME registry. This is fast but unreliable: anyone can rename a .exe file to .jpg and extension-based detection will report image/jpeg.

Content-based detection reads the actual file content and looks for "magic bytes", specific byte sequences at the start of a file that identify the format. A JPEG always starts with FF D8 FF. A PDF always starts with %PDF. A ZIP file starts with PK. Reading these bytes tells you what the file actually is, regardless of its extension.

ToolHQ's MIME checker uses content-based detection when you upload a file, and extension-based lookup when you enter an extension. The content-based result is more reliable and catches misnamed files.

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When knowing the MIME type matters

Web server configuration: If your server is sending files with incorrect Content-Type headers, browsers may display them wrong. A common issue: .woff2 font files served without font/woff2 trigger CORS errors in some browsers. An .svg file served as text/plain won't render as an image. Checking the MIME type helps diagnose these problems.

File upload validation: Web applications that accept user file uploads need to validate the actual file type, not just the extension. A malicious user can rename a .php file to .jpg and try to upload it. Content-based MIME detection catches this.

API development: REST APIs that serve files need to set the correct Content-Type response header. If you are building an endpoint that serves images, PDFs, or downloads, you need the exact MIME string for each file type.

Email attachments: Email clients use MIME types to determine how to display or handle attachments. Incorrect MIME types can cause attachments to display inline when they should download, or vice versa.

Build tools and bundlers: Web bundlers and CDN configurations often require explicit MIME type mappings for non-standard file types (like .wasm for WebAssembly, which needs application/wasm, or .avif for AVIF images).

Priya, a front-end developer, was deploying a web app that used WebP images. After deployment, some images were not rendering in Safari. She checked the server's MIME configuration using ToolHQ's MIME type checker, uploaded a .webp file, and confirmed it was returning image/webp. The issue turned out to be in the CDN configuration, it was stripping the Content-Type header and falling back to application/octet-stream. Once she fixed the CDN MIME mapping, the images rendered correctly in all browsers.

Check any file's MIME type now, free, browser-based, instant

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How to use ToolHQ's MIME type checker

Check by file upload:

1. Open https://www.toolhq.app/tools/mime-type-checker.
2. Upload the file by clicking the upload area or dragging it in.
3. The tool reads the file's content in your browser and identifies the MIME type from the actual binary data.
4. The result shows the detected MIME type, file size, and any relevant notes.

Check by file extension:

1. Type a file extension (e.g., .pdf, .mp4, .svg) into the extension field.
2. The tool returns the standard MIME type for that extension from the IANA registry.

Since file reading happens in your browser, no file content is sent to any server. For sensitive files (documents, code files, private data), the privacy guarantee is meaningful.

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MIME types for common web development scenarios

Serving fonts: Incorrect MIME types for web fonts cause browser security warnings and CORS failures.

• WOFF: font/woff
• WOFF2: font/woff2
• TTF: font/ttf

Serving modern image formats:

• WebP: image/webp
• AVIF: image/avif
• HEIC: image/heic

JavaScript modules and JSON:

• ES modules: text/javascript (not application/javascript, which is deprecated)
• JSON: application/json
• JSON-LD: application/ld+json

WebAssembly:

• WASM: application/wasm (required for browser execution)

For related tools, the archive converter works with ZIP, TAR, and other archive formats whose MIME types you might be checking. The hash generator computes file hashes for verification, and the URL encoder decoder handles encoding MIME type strings for use in URLs.

Daniel, a backend developer, was setting up file upload validation for a document management system. The spec required accepting only PDF and Word documents. He needed the exact MIME types to implement the check. He used ToolHQ to check sample files of each format: .pdf returned application/pdf, .docx returned application/vnd.openxmlformats-officedocument.wordprocessingml.document. He used those exact strings in the validation logic. When a user tried to upload a renamed .exe file as .pdf, the content-based detection caught it.

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Frequently asked questions

What is the MIME type for JSON?

application/json is the registered MIME type for JSON data. It is used in Content-Type headers for API responses (Content-Type: application/json) and in Accept headers when a client requests JSON.

What does application/octet-stream mean?

It is the default MIME type for unknown binary data, "this is bytes, type unknown." Browsers typically prompt a download when they receive this type. If a file you serve shows as application/octet-stream when it should be something specific, check your server's MIME type configuration.

Can two files have the same MIME type but different extensions?

Yes. .jpg and .jpeg both map to image/jpeg. .htm and .html both map to text/html. MIME types describe the format, not the naming convention.

Why is text/javascript preferred over application/javascript?

The IANA officially registered text/javascript as the correct MIME type for JavaScript, and application/javascript was deprecated (via RFC 9239 in 2022). Modern web servers and tools should use text/javascript.

How do I check what MIME type my web server is sending?

Open your browser's developer tools (F12), go to the Network tab, click the file in the request list, and look at the Content-Type response header. Alternatively, use a tool like the SSL checker or command-line curl -I to see response headers.

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The short version

MIME types tell software what a file contains. Web servers send them in Content-Type headers; browsers use them to decide how to render or handle a response; APIs require them in request and response definitions. Getting them wrong produces subtle bugs.

ToolHQ's MIME type checker identifies types from actual file content (magic bytes detection) or from a file extension, runs entirely in your browser, and sends no file content anywhere.

For related file operations, the archive converter handles ZIP and TAR files, and the hash generator verifies file integrity.

Check any MIME type free, browser-based, no upload to servers

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