Lookup MIME types and file extension mappings. Part of the DevTools Surf developer suite. Browse more tools in the Info / Guides collection.
Use Cases
Look up the correct Content-Type header for a file extension before setting it in a server response.
Find the file extension for a MIME type received in an API response to determine how to handle it.
Verify which MIME types a browser can render natively vs. those that trigger a download.
Identify the correct multipart/* subtype for form submissions, file uploads, or email attachments.
Tips
Use 'application/octet-stream' as the fallback MIME type for unknown binary files — browsers will prompt a download rather than attempting to render.
Set Content-Type headers precisely — sending HTML as text/plain prevents the browser from parsing it; sending CSV as text/plain works but prevents auto-download behavior.
Check the IANA registry link for official MIME types before using non-standard types — unofficial types should use the x- prefix by convention (e.g., application/x-custom).
Fun Facts
MIME (Multipurpose Internet Mail Extensions) was defined in RFC 1341 in 1992 to allow email to carry non-ASCII content. The same mechanism was later adapted for HTTP Content-Type headers.
There are over 1,900 registered MIME types in the IANA registry as of 2024, covering media, application, text, model, font, and message categories. New types are registered via formal IANA review.
The 'application/json' MIME type was officially registered in RFC 4627 in 2006 — despite JSON being in widespread use for several years before the MIME type was formally standardized.
FAQ
What's the difference between text/html and application/xhtml+xml?
text/html is parsed in HTML mode (lenient). application/xhtml+xml is parsed as strict XML — a single malformed tag causes a parse error instead of recovery. Use text/html for all modern web pages.
What MIME type should I use for JSON?
application/json is the correct type for JSON API responses. text/json is non-standard. application/geo+json and application/ld+json are registered subtypes for specific JSON-based formats.
Does MIME type affect SEO?
Indirectly — search engines crawl content-type to determine how to parse responses. HTML served as text/plain may not be indexed correctly. Serving non-text content as text/* can cause indexing failures.
