How mime type lookup works
A MIME type (officially a media type) is the two-part label a web server sends with every file — image/png, application/pdf, text/html — so the browser knows how to handle it. The mapping runs in both directions, and this tool handles both: enter an extension like pdf or .pdf to get its content type, or enter a type like image/png to see which extensions use it. The category (text, image, audio, video, application, font) comes from the type’s first half and is shown on every row.
The mapping is genuinely many-to-many, and the table is honest about it. One extension can carry several types (.webm is video/webm for video and audio/webm for audio); one type can own several extensions (image/jpeg covers both .jpg and .jpeg); and some historic types were never registered but won anyway (image/x-icon for favicons). Where common practice disagrees with the IANA registry, the note column says so — for example JavaScript is officially text/javascript as of RFC 9239, even though plenty of older stacks still send application/javascript.
When a server sends no type, browsers fall back to application/octet-stream — "a stream of bytes" — and often download the file instead of displaying it, which is the single most common cause of files "downloading instead of opening". Knowing the right type fixes that: HTML needs text/html or your page renders as plain text, CSS needs text/css, and JSON APIs should send application/json. The common-types table below the search covers the two dozen types that account for nearly all day-to-day web traffic.