`express.json()`

Built-in middleware that parses incoming JSON request bodies into req.body.

Since Express 4.16 Spec ↗

Syntax

express.json([options])

Parameters

Name	Type	Required	Description
`options`	`object`	No	`limit` (max body size), `strict`, `type`, `verify`, `reviver`.

Returns

function — A middleware function.

Examples

app.use(express.json({ limit: '100kb' }));

app.post('/echo', (req, res) => res.json(req.body));

Output

$ curl -X POST -d '{"a":1}' -H 'Content-Type: application/json' localhost:3000/echo
{"a":1}

app.use(express.json());

app.use((err, req, res, next) => {
  if (err.type === 'entity.parse.failed') {
    return res.status(400).json({ error: 'invalid JSON' });
  }
  next(err);
});

Output

(400) {"error":"invalid JSON"}

Notes

Only parses requests whose `Content-Type` is JSON, leaving others untouched. Always set a `limit` to prevent large-payload denial-of-service. Malformed JSON triggers a 400 via the error pipeline - handle it with error middleware.