diff --git a/Gemfile.lock b/Gemfile.lock
new file mode 100644
index 0000000..e1d793e
--- /dev/null
+++ b/Gemfile.lock
@@ -0,0 +1,110 @@
+PATH
+  remote: .
+  specs:
+    xmon (0.1.0)
+      activesupport (~> 7.0.8)
+      colorize
+      dnsruby
+      httparty
+      ruby-nmap
+      slop
+      whois-parser
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    activesupport (7.0.8.1)
+      concurrent-ruby (~> 1.0, >= 1.0.2)
+      i18n (>= 1.6, < 2)
+      minitest (>= 5.1)
+      tzinfo (~> 2.0)
+    ast (2.4.2)
+    coderay (1.1.3)
+    colorize (1.1.0)
+    command_mapper (0.3.2)
+    concurrent-ruby (1.2.3)
+    dnsruby (1.70.0)
+      simpleidn (~> 0.2.1)
+    httparty (0.21.0)
+      mini_mime (>= 1.0.0)
+      multi_xml (>= 0.5.2)
+    i18n (1.14.4)
+      concurrent-ruby (~> 1.0)
+    json (2.7.1)
+    language_server-protocol (3.17.0.3)
+    lint_roller (1.1.0)
+    method_source (1.0.0)
+    mini_mime (1.1.5)
+    minitest (5.22.2)
+    multi_xml (0.6.0)
+    nokogiri (1.16.2-arm64-darwin)
+      racc (~> 1.4)
+    parallel (1.24.0)
+    parser (3.3.0.5)
+      ast (~> 2.4.1)
+      racc
+    pry (0.14.2)
+      coderay (~> 1.1)
+      method_source (~> 1.0)
+    racc (1.7.3)
+    rainbow (3.1.1)
+    rake (13.1.0)
+    regexp_parser (2.9.0)
+    rexml (3.2.6)
+    rubocop (1.62.0)
+      json (~> 2.3)
+      language_server-protocol (>= 3.17.0)
+      parallel (~> 1.10)
+      parser (>= 3.3.0.2)
+      rainbow (>= 2.2.2, < 4.0)
+      regexp_parser (>= 1.8, < 3.0)
+      rexml (>= 3.2.5, < 4.0)
+      rubocop-ast (>= 1.31.1, < 2.0)
+      ruby-progressbar (~> 1.7)
+      unicode-display_width (>= 2.4.0, < 3.0)
+    rubocop-ast (1.31.2)
+      parser (>= 3.3.0.4)
+    rubocop-performance (1.20.2)
+      rubocop (>= 1.48.1, < 2.0)
+      rubocop-ast (>= 1.30.0, < 2.0)
+    ruby-nmap (1.0.3)
+      command_mapper (~> 0.3)
+      nokogiri (~> 1.3)
+    ruby-progressbar (1.13.0)
+    simpleidn (0.2.1)
+      unf (~> 0.1.4)
+    slop (4.10.1)
+    standard (1.34.0)
+      language_server-protocol (~> 3.17.0.2)
+      lint_roller (~> 1.0)
+      rubocop (~> 1.60)
+      standard-custom (~> 1.0.0)
+      standard-performance (~> 1.3)
+    standard-custom (1.0.2)
+      lint_roller (~> 1.0)
+      rubocop (~> 1.50)
+    standard-performance (1.3.1)
+      lint_roller (~> 1.1)
+      rubocop-performance (~> 1.20.2)
+    tzinfo (2.0.6)
+      concurrent-ruby (~> 1.0)
+    unf (0.1.4)
+      unf_ext
+    unf_ext (0.0.9.1)
+    unicode-display_width (2.5.0)
+    whois (5.1.1)
+    whois-parser (2.0.0)
+      activesupport (>= 4)
+      whois (>= 4.1.0)
+
+PLATFORMS
+  arm64-darwin-22
+
+DEPENDENCIES
+  pry
+  rake (~> 13.0)
+  standard (~> 1.3)
+  xmon!
+
+BUNDLED WITH
+   2.4.22
diff --git a/README.md b/README.md
index 5fd90e2..a8178f8 100644
--- a/README.md
+++ b/README.md
@@ -1,8 +1,8 @@
 # Xmon
 
-TODO: Delete this and the text below, and describe your gem
+Yet another network monitoring tool
 
-Welcome to your new gem! In this directory, you'll find the files you need to be able to package up your Ruby library into a gem. Put your Ruby code in the file `lib/xmon`. To experiment with that code, run `bin/console` for an interactive prompt.
+Use DSL to describe your network and services, run periodic checks and get notified when something changes.
 
 ## Installation
 
@@ -18,7 +18,13 @@ If bundler is not being used to manage dependencies, install the gem by executin
 
 ## Usage
 
-TODO: Write usage instructions here
+Create definition file like <examples/nic.rb>
+
+Run monitor 
+
+```
+    bin/xmon -d examples/nic.rb
+```
 
 ## Development
 
diff --git a/bin/xmon b/bin/xmon
new file mode 100755
index 0000000..009053b
--- /dev/null
+++ b/bin/xmon
@@ -0,0 +1,30 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require "bundler/setup"
+require "xmon"
+require "slop"
+require "irb"
+
+begin
+opts = Slop.parse do |o|
+  o.banner = "Usage: xmon [options]"
+  o.array '-d', '--definition', 'Definition file to load', required: true
+  o.on '-v', '--version' do
+    puts "1.1.1"
+    exit
+  end
+
+  o.on '-h', '--help' do
+    puts o
+    exit
+  end
+end
+rescue Slop::Error => e
+  puts e
+  exit
+end
+
+opts[:definition].each do |file|
+  Xmon.load(file).check
+end
diff --git a/examples/nic.rb b/examples/nic.rb
new file mode 100644
index 0000000..928c0a6
--- /dev/null
+++ b/examples/nic.rb
@@ -0,0 +1,27 @@
+describe "nic.cz", type: :domain do
+  describe :rdap do
+    status :server_transfer_prohibited
+    registrar "REG-CZNIC"
+    registrant "CZ-NIC"
+    expires "2027-03-14"
+  end
+
+  describe :dns do
+    dnssec :valid
+    nameservers ["a.ns.nic.cz", "b.ns.nic.cz", "d.ns.nic.cz"]
+    record "www", :a, "217.31.205.50"
+    record "www", :aaaa, "2001:1488:0:3::2"
+  end
+end
+
+describe "217.31.205.50", type: :ipv4 do
+  port 80, type: :tcp do
+    status :open
+  end
+  port 443, type: :tcp, protocol: :https do
+    host "www.nic.cz"
+    server "nginx"
+    status_code 200
+    cert_sn "04E732C227971E1E92114CE4E26657CD6258"
+  end
+end
diff --git a/lib/xmon.rb b/lib/xmon.rb
index 79a7b7f..e1d0bbc 100644
--- a/lib/xmon.rb
+++ b/lib/xmon.rb
@@ -1,8 +1,46 @@
 # frozen_string_literal: true
 
+require "pry"
+require "colorize"
+# require 'net/protocol'
+
 require_relative "xmon/version"
+require_relative "xmon/descriptions"
+
+require_relative "xmon/tcp"
+require_relative "xmon/ssl"
+require_relative "xmon/dns"
+require_relative "xmon/rdap"
 
 module Xmon
   class Error < StandardError; end
-  # Your code goes here...
+
+  def self.compare(a, b)
+    if a == b
+      [:ok, a]
+    else
+      [:fail, a, b]
+    end
+  end
+
+  def self.print_results(results)
+    # puts "Results: #{results.inspect}".colorize(:blue)
+    results.each do |res|
+      res.each do |r|
+        if r.is_a?(Array)
+          if r[0] == :ok
+            puts "OK: #{r[1]}".colorize(:green)
+          else
+            puts "FAIL: #{r[1]} != #{r[2]}".colorize(:red)
+          end
+        end
+      end
+    end
+  end
+
+  def self.load(file)
+    d = Description.new
+    d.instance_eval(File.read(file))
+    d
+  end
 end
diff --git a/lib/xmon/descriptions.rb b/lib/xmon/descriptions.rb
new file mode 100644
index 0000000..1157d80
--- /dev/null
+++ b/lib/xmon/descriptions.rb
@@ -0,0 +1,94 @@
+module Xmon
+  class Description
+    def initialize
+      @descriptions = []
+    end
+
+    def define_attributes(attributes)
+      attributes.each do |m|
+        self.class.send(:define_method, m) do |*args|
+          if args[0]
+            instance_variable_set(:"@#{m}", args[0])
+          else
+            instance_variable_get(:"@#{m}")
+          end
+        end
+      end
+    end
+
+    def describe(*args, **kwargs, &)
+      unless @description
+        if kwargs[:type] == :domain
+          @description = DomainDescription.new(args[0])
+        elsif kwargs[:type] == :ipv4
+          @description = IPv4Description.new(args[0])
+        else
+          puts "unknown block given with args: #{args} and kwargs: #{kwargs}"
+          @description = Description.new
+        end
+      end
+
+      if block_given?
+        @description.instance_eval(&)
+      else
+        @description = @description.class.new(*args, **kwargs)
+      end
+      @descriptions ||= []
+      @descriptions << @description
+      @description = nil
+    end
+
+    def status(status) # standard:disable Style/TrivialAccessors
+      @status = status
+    end
+
+    def check
+      @results = []
+      (@descriptions || []).each { |d|
+        puts "#{d.class} #{@name}".colorize(:yellow)
+        res = d.check
+        @results << res
+
+        Xmon.print_results([res])
+      }
+    end
+  end
+
+  class DomainDescription < Description
+    def initialize(name, *)
+      @name = name
+    end
+
+    def describe(*args, **kwarg)
+      if args == [:rdap]
+        @description = Xmon::RDAP.new(@name)
+      elsif args == [:dns]
+        @description = Xmon::DNS.new(@name)
+      end
+      super
+    end
+  end
+
+  class IPv4Description < Description
+    def initialize(address, *)
+      @address = address
+    end
+
+    def describe(*, **kwargs)
+      if kwargs[:type] == :tcp
+        @description = if kwargs[:protocol] == :https
+          Xmon::SSL.new(@address, *, **kwargs)
+        else
+          Xmon::TCP.new(@address, *, **kwargs)
+        end
+      elsif kwargs[:type] == :udp
+        @description = Xmon::UDP.new(*, **kwargs)
+      end
+      super
+    end
+
+    def port(...)
+      describe(...)
+    end
+  end
+end
diff --git a/lib/xmon/dns.rb b/lib/xmon/dns.rb
new file mode 100644
index 0000000..085c6af
--- /dev/null
+++ b/lib/xmon/dns.rb
@@ -0,0 +1,28 @@
+require "dnsruby"
+
+module Xmon
+  class DNS < Description
+    def initialize(domain)
+      @domain = domain
+      define_attributes([:nameservers, :records, :dnssec])
+    end
+
+    def record(name, type, value)
+      @records ||= []
+      @records << {name: name, type: type, value: value}
+    end
+
+    def fetch(record, type = "A")
+      Dnsruby::Resolver.new.query(record, type).answer.map { |a| a.respond_to?(:address) ? a.address : a.rdata }.flatten.map(&:to_s).sort
+    end
+
+    def check
+      r = [Xmon.compare(@nameservers, fetch(@domain, "NS"))]
+
+      @records.each do |record|
+        r << Xmon.compare(record[:value], fetch(record[:name] + "." + @domain, record[:type].to_s.upcase).sort.join(","))
+      end
+      r
+    end
+  end
+end
diff --git a/lib/xmon/rdap.rb b/lib/xmon/rdap.rb
new file mode 100644
index 0000000..b0fa2b1
--- /dev/null
+++ b/lib/xmon/rdap.rb
@@ -0,0 +1,30 @@
+require "httparty"
+
+module Xmon
+  class RDAP < Description
+    def initialize(domain, **opts)
+      @domain = domain
+      define_attributes([:registrant, :registrar, :expires])
+    end
+
+    def fetch(record)
+      response = HTTParty.get("https://rdap.nic.cz/domain/#{record}")
+      response = JSON.parse(response.body, symbolize_names: true)
+      {
+        registrant: response[:entities].detect { |a| a[:roles] == ["registrant"] }[:handle],
+        registrar: response[:entities].detect { |a| a[:roles] == ["registrar"] }[:handle],
+        nameservers: response[:nameservers].map { |a| a[:ldhName] }.sort,
+        expiration: response[:events].detect { |a| a[:eventAction] == "expiration" }[:eventDate],
+        status: response[:status].map { |s| s.split(" ").join("_") }.sort.join("_").to_sym
+      }
+    end
+
+    def check
+      checker = fetch(@domain)
+      [Xmon.compare(@status, checker[:status]),
+        Xmon.compare(@registrant, checker[:registrant]),
+        Xmon.compare(@registrar, checker[:registrar]),
+        Xmon.compare(@expires, checker[:expiration][0, 10])]
+    end
+  end
+end
diff --git a/lib/xmon/ssl.rb b/lib/xmon/ssl.rb
new file mode 100644
index 0000000..1b5592a
--- /dev/null
+++ b/lib/xmon/ssl.rb
@@ -0,0 +1,48 @@
+module Xmon
+  class SSL < TCP
+    def initialize(address, *args, **kwargs)
+      @host = kwargs[:host]
+      @path = kwargs[:path] || "/"
+      define_attributes([:host, :status_code, :server, :cert_sn, :location])
+      super
+    end
+
+    def fetch(host, name = nil, port = 443, path = "/")
+      ctx = OpenSSL::SSL::SSLContext.new
+      sock = TCPSocket.new(host, port)
+      ssl = OpenSSL::SSL::SSLSocket.new(sock, ctx)
+      ssl.hostname = name if name
+      ssl.sync_close = true
+      ssl.connect
+      cert = ssl.peer_cert
+      request = "GET / HTTP/1.1\r\nHost: #{name}\r\nConnection: close\r\n\r\n"
+      ssl.write request
+      header = ssl.gets("\r\n\r\n")
+      begin
+        body = ssl.read
+      rescue OpenSSL::SSL::SSLError
+        body = ""
+      end
+
+      status, header = header.split("\r\n", 2)
+      _protocol, status_code, _status_text = status.split(" ", 3)
+      {
+        cert_sn: cert.serial.to_s(16),
+        status_code: status_code.to_i,
+        headers: header.split("\r\n").map { |a| a.split(": ") }.to_h,
+        body: body
+      }
+    end
+
+    def check
+      puts "checking SSL for #{@address} #{@host} #{@port} #{@path}"
+      current = fetch(@address, @host, @port, @path)
+      r = []
+      r << Xmon.compare(@status_code, current[:status_code]) if @status_code
+      r << Xmon.compare(@server, current.dig(:headers, "Server")) if @server
+      r << Xmon.compare(@cert_sn, current[:cert_sn]) if @cert_sn
+      r << Xmon.compare(@location, current.dig(:headers, "Location")) if @location
+      r
+    end
+  end
+end
diff --git a/lib/xmon/tcp.rb b/lib/xmon/tcp.rb
new file mode 100644
index 0000000..8fb41ec
--- /dev/null
+++ b/lib/xmon/tcp.rb
@@ -0,0 +1,49 @@
+require "nmap/command"
+require "nmap/xml"
+
+module Xmon
+  class TCP < Description
+    def initialize(address, *args, **kwargs)
+      @address = address
+      @port = args[0]
+      @protocol = kwargs[:protocol]
+    end
+
+    def key(type, value)
+      @keys ||= []
+      @keys << {type: type, value: value}
+    end
+
+    def fetch(host, ports, protocol = :tcp)
+      File.delete("nmap.xml") if File.exist?("nmap.xml")
+      Nmap::Command.new do |nmap|
+        nmap.skip_discovery = true
+        nmap.targets = host
+        nmap.udp_scan = true if protocol == :udp
+        nmap.ports = ports
+        nmap.syn_scan = false
+        nmap.service_scan = true
+        nmap.verbose = 0
+        nmap.output_xml = "nmap.xml"
+      end.run_command
+      Nmap::XML.open("nmap.xml") do |xml|
+        @out = xml.hosts.map do |host|
+          host.ports.map do |port|
+            {
+              host: host.ip,
+              port: port.number,
+              protocol: port.protocol,
+              state: port.state
+            }
+          end
+        end
+      end
+      @out.flatten
+    end
+
+    def check
+      checker = fetch(@address, @port, :tcp)
+      [Xmon.compare(@status, checker[0][:state])]
+    end
+  end
+end
diff --git a/lib/xmon/udp.rb b/lib/xmon/udp.rb
new file mode 100644
index 0000000..ae11cb7
--- /dev/null
+++ b/lib/xmon/udp.rb
@@ -0,0 +1,9 @@
+module Xmon
+  class UDP < Description
+    def initialize(address, *args, **kwargs)
+      @address = address
+      @port = args[0]
+      @protocol = kwargs[:protocol]
+    end
+  end
+end
diff --git a/lib/xmon/whois.rb b/lib/xmon/whois.rb
new file mode 100644
index 0000000..b66df79
--- /dev/null
+++ b/lib/xmon/whois.rb
@@ -0,0 +1,9 @@
+require "whois-parser"
+
+module Xmon
+  class Whois < Description
+    def fetch(record)
+      ::Whois.whois(record)
+    end
+  end
+end
diff --git a/xmon.gemspec b/xmon.gemspec
index a4f09c5..eb9e798 100644
--- a/xmon.gemspec
+++ b/xmon.gemspec
@@ -8,17 +8,17 @@ Gem::Specification.new do |spec|
   spec.authors = ["Jiří Kubíček"]
   spec.email = ["jiri.kubicek@kraxnet.cz"]
 
-  spec.summary = "TODO: Write a short summary, because RubyGems requires one."
-  spec.description = "TODO: Write a longer description or delete this line."
-  spec.homepage = "TODO: Put your gem's website or public repo URL here."
+  spec.summary = "Yet another network monitoring tool"
+  spec.description = "Use DSL to describe your network and services, run periodic checks and get notified when something changes."
+  spec.homepage = "https://github.com/kraxnet/xmon"
   spec.license = "MIT"
   spec.required_ruby_version = ">= 2.6.0"
 
-  spec.metadata["allowed_push_host"] = "TODO: Set to your gem server 'https://example.com'"
+  spec.metadata["allowed_push_host"] = "https://rubygems.org"
 
   spec.metadata["homepage_uri"] = spec.homepage
-  spec.metadata["source_code_uri"] = "TODO: Put your gem's public repo URL here."
-  spec.metadata["changelog_uri"] = "TODO: Put your gem's CHANGELOG.md URL here."
+  spec.metadata["source_code_uri"] = "https://github.com/kraxnet/xmon.git"
+  spec.metadata["changelog_uri"] = "https://github.com/kraxnet/xmon/commits"
 
   # Specify which files should be added to the gem when it is released.
   # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
@@ -32,8 +32,14 @@ Gem::Specification.new do |spec|
   spec.executables = spec.files.grep(%r{\Aexe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 
-  # Uncomment to register a new dependency of your gem
-  # spec.add_dependency "example-gem", "~> 1.0"
+  spec.add_dependency "slop"
+  spec.add_dependency "whois-parser"
+  spec.add_dependency "httparty"
+  spec.add_dependency "dnsruby"
+  spec.add_dependency "ruby-nmap"
+  spec.add_dependency "activesupport", "~> 7.0.8"
+  spec.add_dependency "colorize"
+  spec.add_development_dependency "pry"
 
   # For more information and examples about making a new gem, check out our
   # guide at: https://bundler.io/guides/creating_gem.html