Content Type

About

The Content-Type is an HTTP header used to indicate the media type (also called MIME type) of the data being sent in the body of an HTTP request or response. It tells the server or client how to interpret the content of the message body.

Why is Content-Type Important?

APIs often exchange data in formats like JSON, XML, HTML, plain text, etc. The Content-Type header helps ensure that:

• The server knows how to parse the incoming request body

• The client knows how to handle the response body

If the Content-Type is missing or incorrect, the receiver may fail to understand or parse the data correctly.

Usage

In a Request

When a client (like Postman, browser, or frontend app) sends data to the server, it must specify the format using the Content-Type header.

Example:

POST /api/users
Content-Type: application/json

{
  "name": "John",
  "email": "[email protected]"
}

The server will use this header to determine how to read the request body — in this case, as JSON.

In a Response

When the server responds, it can also set the Content-Type to tell the client what format the response body is in.

Example:

HTTP/1.1 200 OK
Content-Type: application/xml

<user>
  <name>John</name>
  <email>[email protected]</email>
</user>

Possible Content-Type Values

Content-Type	Description
application/json	JSON data. Most common format in REST APIs.
application/xml	XML data. Used in older APIs and some enterprise systems.
text/plain	Plain text data with no formatting.
text/html	HTML content, used in web pages.
application/x-www-form-urlencoded	Form data encoded in key-value pairs (like key=value&key2=value2). Default for HTML forms.
multipart/form-data	Used for form submissions that include files (e.g., image uploads).
application/octet-stream	Binary data; generic for any file (used in downloads or file streams).
application/pdf	PDF files.
application/zip	ZIP compressed files.
application/javascript	JavaScript files.
text/css	CSS stylesheets.
image/png	PNG image.
image/jpeg	JPEG image.
image/gif	GIF image.
image/svg+xml	SVG (Scalable Vector Graphics) in XML format.
audio/mpeg	MP3 audio format.
audio/wav	WAV audio format.
video/mp4	MP4 video format.
video/x-msvideo	AVI video format.
application/vnd.api+json	JSON:API specification format.
application/graphql	GraphQL query format.
application/ld+json	Linked Data using JSON (used in semantic web, schema.org).
application/soap+xml	SOAP XML format (used in SOAP-based APIs).
application/vnd.ms-excel	Microsoft Excel (XLS) file.
application/vnd.openxmlformats-officedocument.spreadsheetml.sheet	Microsoft Excel (XLSX) file.
application/msword	Microsoft Word (DOC) file.
application/vnd.openxmlformats-officedocument.wordprocessingml.document	Microsoft Word (DOCX) file.
application/x-yaml	YAML format (not standard but used in APIs and config services).
application/x-protobuf	Protocol Buffers (binary serialization format).
application/x-ndjson	Newline-delimited JSON (used in streaming APIs).

Relation to Accept Header

• Content-Type is used to indicate the format being sent.

• Accept is used to indicate the format expected in response.

Example:

POST /api/data
Content-Type: application/json
Accept: application/xml

This means:

• "I’m sending you JSON"

• "Please respond with XML"

Content-Type in API Frameworks (like Spring)

In Java Spring (or similar frameworks):

• To define what our API accepts, use consumes = MediaType.APPLICATION_JSON_VALUE

• To define what our API returns, use produces = MediaType.APPLICATION_XML_VALUE

Example:

@PostMapping(value = "/users", consumes = "application/json", produces = "application/xml")
public UserResponse createUser(@RequestBody UserRequest user) {
    ...
}

What Happens if Content-Type is Missing ?

• The server might reject the request (415 Unsupported Media Type)

• The server might default to another format and incorrectly parse the data

• The client might misinterpret the response content