What is a Content-Type header?

The HTTP Content-Type header tells the client what kind of data the response body contains, such as text/html; charset=utf-8. Browsers and APIs rely on it to parse, render, or download the payload correctly.

When do I add charset=utf-8?

Add charset=utf-8 to text-based types like text/html, text/plain, and text/css to declare the byte encoding. For application/json the charset is implicitly UTF-8 per spec, so it is usually omitted.

What is the difference between a type and a subtype?

A MIME type has the form type/subtype, for example image/png. The top-level type (image) groups the broad category, and the subtype (png) names the exact format. Vendor subtypes use a vnd. prefix.

Why use application/octet-stream?

application/octet-stream is the generic 'arbitrary binary data' type. Servers send it when no more specific type is known, which usually prompts the browser to download rather than display the file.

Does this run offline?

Yes. The media-type database ships with the page and all lookups happen in your browser, so nothing is sent to a server and it works without a connection.

Content-Type Lookup — Gera Tools

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Content-Type lookup

The HTTP Content-Type header carries a MIME (media) type that tells clients how to interpret a response body — render it, parse it, or download it. This tool is the reverse of an extension lookup: search by format name, file extension, or top-level type and get the exact type/subtype string, the extensions it covers, and the parameters (like charset) you should include.

How it works

Each record pairs a canonical MIME type with its top-level type (text, image, audio, video, application, font), its matching file extensions, and any standard parameters. The search normalizes your query and matches it against the type string, the format name, and the extensions, so json, .json, and application all surface the relevant entry. Text formats include the recommended charset=utf-8 parameter; binary formats omit it.

Tips and example

Set the header with the parameter where appropriate:

Content-Type: text/html; charset=utf-8
Content-Type: application/json
Content-Type: image/png
Content-Type: application/octet-stream

For downloads, pair application/octet-stream with a Content-Disposition: attachment header to force a save dialog.
application/json is defined as UTF-8, so adding charset is redundant though harmless.
When a precise type is unknown, application/octet-stream is the safe generic fallback.