Question: I have many of these "controllers": 

```
app.get('/',function(req,res){
    var stuff = { 'title': 'blah' };
    res.render('mytemplate',stuff);
});    

```

Notice res.render? I want to add this header to every response header I make:

`X-XSS-Protection: 0`

How can I add that response header automatically?

Answer: 
you could create your own middleware method like so:

```
addToHeader = function (req, res, next) {
  console.log("add to header called ... " + req.url);
  res.header('X-XSS-Protection', '0');
  next();
}

```

and then change your routes to sth like this:

```
app.get('/', addToHeader, function(req,res){
  var stuff = { 'title': 'blah' };
  res.render('mytemplate',stuff);
});

```

should work.
I'd like to point out that none of these answer actually answer the question; the question is specifically relating to render responses; e.g. for an app like:

```
const router = require('express').Router();
router.use('/test.json', (req, res) => res.json({ test: 'hi' });
router.use('/test.html', (req, res) => res.render('test'));

```

It's not clear how to add headers (e.g. CSP headers, which can be very verbose) *only* to your HTML responses. Express doesn't have a hook to specifically do that. The only option at the moment is to organize your code so you don't have to, e.g.

```
app.use(jsonRouter);
app.use(htmlRouter);

```

...which allows you to do as some of the other answers suggest, and add generic middleware for setting the headers.