What's the Correct JSON Content-Type Header? (application/json Explained)

Quick answer: use application/json. It's the official IANA-registered MIME type for JSON (RFC 4627 / RFC 8259), and every modern client and framework expects it.

Content-Type: application/json

Why you'll see other values floating around

Before application/json was standardized, people experimented with text/javascript, application/x-javascript, and text/x-json. None of these are correct today — they're legacy artifacts from before the JSON MIME type was ratified, and some browsers historically handled them inconsistently.

Setting it correctly in common stacks

// Node / Express
res.setHeader('Content-Type', 'application/json');
res.json(data); // sets the header for you

// PHP
header('Content-Type: application/json');

// fetch() request
fetch(url, {
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify(payload)
});

What about JSONP?

If you're serving runnable JavaScript that wraps JSON in a callback (JSONP — largely obsolete now that CORS exists), the correct type is application/javascript, not application/json, since the response is actual executable script, not pure data.

Does the content type include a charset?

JSON's default encoding is UTF-8, so you generally don't need to add ; charset=utf-8. Some frameworks add it anyway; it's harmless but redundant per RFC 8259.

FAQ

What happens if I send the wrong content type?

Many strict API clients and some frameworks (like Express with express.json()) will refuse to auto-parse the body if the header isn't application/json, leading to confusing "empty body" bugs.

Is text/json ever correct?

No, it was never standardized. Some very old servers emit it, but new code should always send application/json.

This article explains and expands on the community answers to the Stack Overflow question “Which JSON content type do I use?”, used under the CC BY-SA 4.0 license. Screenshot credit: Stack Exchange Inc.

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