Export your wordpress db (post comments, tags and categories) as JSON

wpdb_json_export.rb

require 'active_record'
require 'wpdb'
require 'json'

ActiveRecord::Base.establish_connection(
  :adapter  => 'mysql',
  :host     => 'localhost',
  :port     => 3306,
  :username => 'root',
  :password => '',
  :database => 'your_db_name'
)

post_data = [].tap do |post_data|
  Wpdb::WpPost.posts.published.each do |post|
    data                = {}
    data[:title]        = post.post_title
    data[:slug]         = post.post_name
    data[:body]         = post.post_content
    data[:tags]         = post.wp_tags
    data[:categories]   = post.wp_categories
    data[:published_at] = post.post_date
    post.wp_comments.each do |comment|
      (data[:comments]||=[]) << comment.attributes
    end
    post_data << data
  end
end

puts post_data.to_json
# or even XML
puts post_data.to_xml