How to set the default format for a route in Rails?

Default format for requests:

You can set the default format of a given route to xml using the defaults hash.

Examples:

# single match defaulting to XML (/plots/1 is the same as /plots/1.xml)
match 'posts/:id' => 'posts#show', :defaults => { :format => 'xml' }

# using resources, defaulting to XML (all action use XML by default)
resources :posts, :defaults => { :format => 'xml' }

# using resources and mixing with other options
resources :posts,
          :only => [:new, :create, :destroy],
          :defaults => { :format => 'xml' }

It's always a good idea to search the official Ruby on Rails routing guide, it's fairly in-depth and a very good first-stop resource for any routing issues.

If you only want to support one format and treat all requests as that format, you could use a filter to change it:

before_filter :set_format

def set_format
  request.format = 'xml'
end