Look up MIME types by extension, name or IANA type
A MIME type (Multipurpose Internet Mail Extensions), also called a media type, is the IANA-standardised identifier that indicates a content format, used in HTTP headers (Content-Type), emails, file uploads and APIs. The structure is always type/subtype, such as image/jpeg, application/json or text/html, and it can carry optional parameters like charset=utf-8. The top-level type describes the general category (text, image, audio, video, application, font, multipart) and the subtype pinpoints the specific format. It is the Content-Type, not the file extension, that determines how the browser interprets a response: the same .json served as text/plain will not be treated as JSON. This checker covers the most common types from the IANA registry and practical web use, letting you search by extension (pdf, webp, wasm) or by the full type (application/json), all locally in your browser.
A media type always follows the form type/subtype. The top-level type is a closed category defined by IANA, text, image, audio, video, application, font, model and multipart, and the subtype identifies the exact format within it. Some subtypes carry a structured suffix after a plus sign, such as +json or +xml (for example image/svg+xml), which tells you the base syntax the format is serialized in.
There are also prefix conventions worth knowing: subtypes with vnd. are vendor registrations (application/vnd.ms-excel), and the old x- prefix marked experimental types before standardisation. Optional parameters come after a semicolon, with charset=utf-8 being the most common for text types.
Example 1, serving a WebAssembly module. The correct MIME for a .wasm file is application/wasm. If the server delivers it as application/octet-stream or text/plain, the WebAssembly.instantiateStreaming() API can reject the module in some browsers, because it requires the exact Content-Type. Fixing the type on the server solves loading without touching the code.
Example 2, a JSON upload treated as a download. If a response with a JSON body goes out with Content-Type: application/octet-stream (the generic type for "bytes with no defined format"), the browser tends to offer the file for download instead of processing it. Switching to application/json makes the client interpret the content as expected, confirming that it is the Content-Type, not the extension, that rules.
The Content-Type is set on the server: in nginx via the types{} directive or the standard mime.types; in Node/Express with res.setHeader('Content-Type', ...); in S3 or a CDN via the ContentType metadata on upload. Omitting this header usually makes the browser guess the type (MIME sniffing), which can cause unexpected behavior.
The important limit is that a MIME type is only a declared label, it does not validate the actual file content. A server can announce image/png for a file that is not a PNG, which is exactly why the X-Content-Type-Options: nosniff header exists, preventing the browser from reinterpreting the type. This tool only searches an embedded local database and sends nothing to any server.
Paste the code into your HTML and the tool shows up on your page, without J-Kit's navigation and ads. It still runs in the browser of whoever visits your site.
<iframe
src="https://jkit.tools/embed/en-US/mime-type-checker"
width="100%"
height="600"
style="border:0"
loading="lazy"
title="MIME Type Checker"
></iframe>These references help contextualize formulas, standards, APIs and limitations used on this page. They do not replace professional validation when a result has legal, financial, medical or operational impact.
A MIME type (or media type) is a two-part identifier, type/subtype, that tells the receiver what format a piece of data is in. Originally created for email (Multipurpose Internet Mail Extensions, RFC 2045), it is now ubiquitous in HTTP, where the Content-Type header defines how the browser interprets content.
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