Media type · application/json
application/json
application/json is the media type for JSON documents exchanged between clients and servers.
Key facts
| Type | application/json |
|---|---|
| Extensions | .json |
| Standard | RFC 8259; IANA registry |
| Text or binary | Text (UTF-8 required) |
| Charset parameter | Not defined by the standard |
What application/json is
It identifies a JSON text as defined by RFC 8259. JSON exchanged between systems must be encoded in UTF-8, so the standard does not define a charset parameter; adding one is unnecessary and some strict parsers reject it. The type is used for API requests and responses, configuration files and embedded data.
Why a JSON request returns 400
The most common causes are a body that is not valid JSON (trailing commas, single quotes, unquoted keys), a missing Content-Type: application/json header so the server parses it as form data, or a charset declaration the parser refuses. Validate the exact bytes with a JSON formatter before blaming the server. On the response side, check that the server is not returning HTML error pages with a 200 status — a parser expecting JSON will fail on the first <.
Frequently asked questions
Should application/json include charset=utf-8?
The JSON standard fixes the encoding to UTF-8, so the parameter is not needed. Some APIs send it anyway; a strict parser may ignore or reject it.
Is JSON always UTF-8?
For interchange, yes. RFC 8259 requires UTF-8 for JSON exchanged between systems, even though the grammar itself is Unicode-based.