diff --git a/README.md b/README.md
index 4466705..ecdec56 100644
--- a/README.md
+++ b/README.md
@@ -89,14 +89,14 @@ end
 Render it somewhere. E.g. `app/views/layouts/application.html.erb`:
 
 ```erb
-<%= Omnibar.render %>
+<%= Omnibar.render(self) %>
 ```
 
 If you have a fully decoupled frontend, use `Omnibar.html_url` instead, fetch the omnibar HTML from there, and inject it.
 
 ### Authorization
 
-You can limit access to commands (e.g. search commands). This will not limit access to plain items.
+You can limit access to commands (e.g. search commands) and items.
 
 #### Option 1: globally limit engine access
 
@@ -119,19 +119,35 @@ MyOmnibar.auth = ->(controller, omnibar:) do
 end
 ```
 
+#### Option 3: Item-level conditionality
+
+Items and commands can have an `if` proc that is executed in the controller context. If it returns false, the item is not shown and the command is not executed.
+
+```ruby
+MyOmnibar.add_item(
+  title: 'Admin link',
+  url:   admin_url,
+  if:    ->{ current_user.admin? }
+)
+```
+
+For this to work, the controller context must be given to the omnibar when rendering (e.g. by passing `self` in a view):
+
+```erb
+<%= Omnibar.render(self) %>
+```
+
 ### Using multiple different omnibars
 
 ```ruby
-BaseOmnibar = Class.new(RailsOmnibar)
-BaseOmnibar.configure do |c|
+BaseOmnibar = Class.new(RailsOmnibar).configure do |c|
   c.add_item(
     title: 'Log in',
     url:    Rails.application.routes.url_helpers.log_in_url
   )
 end
 
-UserOmnibar = Class.new(RailsOmnibar)
-UserOmnibar.configure do |c|
+UserOmnibar = Class.new(RailsOmnibar).configure do |c|
   c.auth = ->{ user_signed_in? }
   c.add_item(
     title: 'Log out',
@@ -143,7 +159,15 @@ end
 Then, in some layout:
 
 ```erb
-<%= (user_signed_in? ? UserOmnibar : BaseOmnibar).render %>
+<%= (user_signed_in? ? UserOmnibar : BaseOmnibar).render(self) %>
+```
+
+Omnibars can also inherit commands, configuration, and items from existing omnibars:
+
+```ruby
+SuperuserOmnibar = Class.new(UserOmnibar).configure do |c|
+  # add more items that only superusers should get
+end
 ```
 
 ### Other options and usage patterns
@@ -172,7 +196,7 @@ end
 ```ruby
 module AddOmnibar
   def build_page(...)
-    within(super) { text_node(MyOmnibar.render) }
+    within(super) { text_node(MyOmnibar.render(self)) }
   end
 end
 ActiveAdmin::Views::Pages::Base.prepend(AddOmnibar)
@@ -180,7 +204,7 @@ ActiveAdmin::Views::Pages::Base.prepend(AddOmnibar)
 
 ##### To render in RailsAdmin
 
-Add `MyOmnibar.render` to `app/views/layouts/rails_admin/application.*`.
+Add `MyOmnibar.render(self)` to `app/views/layouts/rails_admin/application.*`.
 
 #### Adding all index routes as searchable items
 
diff --git a/app/controllers/rails_omnibar/html_controller.rb b/app/controllers/rails_omnibar/html_controller.rb
index 87e622c..46bf9d7 100644
--- a/app/controllers/rails_omnibar/html_controller.rb
+++ b/app/controllers/rails_omnibar/html_controller.rb
@@ -1,5 +1,5 @@
 class RailsOmnibar::HtmlController < RailsOmnibar::BaseController
   def show
-    render html: omnibar.render
+    render html: omnibar.render(self)
   end
 end
diff --git a/bin/console b/bin/console
index fe6187e..72848fd 100755
--- a/bin/console
+++ b/bin/console
@@ -2,6 +2,7 @@
 
 require 'bundler/setup'
 require 'rails_omnibar'
+require_relative '../spec/dummy/config/environment'
 
 require 'irb'
 IRB.start(__FILE__)
diff --git a/lib/rails_omnibar/command/base.rb b/lib/rails_omnibar/command/base.rb
index 7781452..8cb1bf6 100644
--- a/lib/rails_omnibar/command/base.rb
+++ b/lib/rails_omnibar/command/base.rb
@@ -1,13 +1,14 @@
 class RailsOmnibar
   module Command
     class Base
-      attr_reader :pattern, :resolver, :description, :example
+      attr_reader :pattern, :resolver, :description, :example, :if
 
-      def initialize(pattern:, resolver:, description: nil, example: nil)
+      def initialize(pattern:, resolver:, description: nil, example: nil, if: nil)
         @pattern = cast_to_pattern(pattern)
         @resolver = RailsOmnibar.cast_to_proc(resolver)
         @description = description
         @example = example
+        @if = RailsOmnibar.cast_to_condition(binding.local_variable_get(:if))
       end
 
       def call(input, controller:, omnibar:)
@@ -19,6 +20,12 @@ def call(input, controller:, omnibar:)
         results.map { |e| RailsOmnibar.cast_to_item(e) }
       end
 
+      def handle?(input, controller:, omnibar:)
+        return false unless pattern.match?(input)
+
+        RailsOmnibar.evaluate_condition(self.if, context: controller, omnibar: omnibar)
+      end
+
       private
 
       def cast_to_pattern(arg)
diff --git a/lib/rails_omnibar/command/search.rb b/lib/rails_omnibar/command/search.rb
index 48d160d..c90ad44 100644
--- a/lib/rails_omnibar/command/search.rb
+++ b/lib/rails_omnibar/command/search.rb
@@ -29,7 +29,7 @@ def initialize(finder:, itemizer:, **kwargs)
 
     # ActiveRecord-specific search.
     class RecordSearch < Search
-      def initialize(model:, columns: :id, pattern: nil, finder: nil, itemizer: nil, example: nil)
+      def initialize(model:, columns: :id, pattern: nil, finder: nil, itemizer: nil, example: nil, if: nil)
         # casting and validations
         model = model.to_s.classify.constantize unless model.is_a?(Class)
         model < ActiveRecord::Base || raise(ArgumentError, 'model: must be a model')
@@ -64,6 +64,7 @@ def initialize(model:, columns: :id, pattern: nil, finder: nil, itemizer: nil, e
           pattern:     pattern,
           finder:      finder,
           itemizer:    itemizer,
+          if:          binding.local_variable_get(:if),
         )
       end
     end
diff --git a/lib/rails_omnibar/commands.rb b/lib/rails_omnibar/commands.rb
index 0f3a658..1f014f0 100644
--- a/lib/rails_omnibar/commands.rb
+++ b/lib/rails_omnibar/commands.rb
@@ -1,17 +1,15 @@
 class RailsOmnibar
   def handle(input, controller)
-    handler = commands.find { |h| h.pattern.match?(input) }
+    handler = commands.find do |cmd|
+      cmd.handle?(input, controller: controller, omnibar: self)
+    end
     handler&.call(input, controller: controller, omnibar: self) || []
   end
 
-  def command_pattern
-    commands.any? ? Regexp.union(commands.map(&:pattern)) : /$NO_COMMANDS/
-  end
-
   def add_command(command)
-    check_const_and_clear_cache
     commands << RailsOmnibar.cast_to_command(command)
-    self
+    clear_command_pattern_cache
+    self.class
   end
 
   def self.cast_to_command(arg)
@@ -43,6 +41,17 @@ def self.cast_to_proc(arg)
 
   private
 
+  def command_pattern
+    @command_pattern ||= begin
+      re = commands.any? ? Regexp.union(commands.map(&:pattern)) : /$NO_COMMANDS/
+      JsRegex.new!(re, target: 'ES2018')
+    end
+  end
+
+  def clear_command_pattern_cache
+    @command_pattern = nil
+  end
+
   def commands
     @commands ||= []
   end
diff --git a/lib/rails_omnibar/conditions.rb b/lib/rails_omnibar/conditions.rb
new file mode 100644
index 0000000..c46abb1
--- /dev/null
+++ b/lib/rails_omnibar/conditions.rb
@@ -0,0 +1,27 @@
+class RailsOmnibar
+  def self.cast_to_condition(arg)
+    case arg
+    when nil, true, false then arg
+    else
+      arg.try(:arity) == 0 ? arg : RailsOmnibar.cast_to_proc(arg)
+    end
+  end
+
+  def self.evaluate_condition(condition, context:, omnibar:)
+    case condition
+    when nil, true then true
+    when false     then false
+    else
+      context || raise(<<~EOS)
+        Missing context for condition, please render the omnibar with `.render(self)`
+      EOS
+      if condition.try(:arity) == 0
+        context.instance_exec(&condition)
+      elsif condition.respond_to?(:call)
+        condition.call(context, controller: context, omnibar: omnibar)
+      else
+        raise("unsupported condition type: #{condition.class}")
+      end
+    end
+  end
+end
diff --git a/lib/rails_omnibar/config.rb b/lib/rails_omnibar/config.rb
index 805afd8..746585c 100644
--- a/lib/rails_omnibar/config.rb
+++ b/lib/rails_omnibar/config.rb
@@ -1,12 +1,14 @@
 class RailsOmnibar
   def configure(&block)
-    check_const_and_clear_cache
     tap(&block)
+    self.class
   end
 
-  attr_reader :auth
   def auth=(arg)
-    @auth = arg.try(:arity) == 0 ? arg : RailsOmnibar.cast_to_proc(arg)
+    config[:auth] = arg.try(:arity) == 0 ? arg : RailsOmnibar.cast_to_proc(arg)
+  end
+  def auth
+    config[:auth]
   end
   def authorize(controller)
     if auth.nil?
@@ -20,33 +22,39 @@ def authorize(controller)
 
   def max_results=(arg)
     arg.is_a?(Integer) && arg > 0 || raise(ArgumentError, 'max_results must be > 0')
-    @max_results = arg
+    config[:max_results] = arg
   end
   def max_results
-    @max_results || 10
+    config[:max_results] || 10
   end
 
-  attr_writer :modal
+  def modal=(arg)
+    config[:modal] = arg
+  end
   def modal?
-    instance_variable_defined?(:@modal) ? !!@modal : false
+    config.key?(:modal) ? !!config[:modal] : false
   end
 
-  attr_writer :calculator
+  def calculator=(arg)
+    config[:calculator] = arg
+  end
   def calculator?
-    instance_variable_defined?(:@calculator) ? !!@calculator : true
+    config.key?(:calculator) ? !!config[:calculator] : true
   end
 
-  def hotkey
-    @hotkey || 'k'
-  end
   def hotkey=(arg)
     arg.to_s.size == 1 || raise(ArgumentError, 'hotkey must have length 1')
-    @hotkey = arg.to_s.downcase
+    config[:hotkey] = arg.to_s.downcase
+  end
+  def hotkey
+    config[:hotkey] || 'k'
   end
 
-  attr_writer :placeholder
+  def placeholder=(arg)
+    config[:placeholder] = arg
+  end
   def placeholder
-    return @placeholder.presence unless @placeholder.nil?
+    return config[:placeholder].presence unless config[:placeholder].nil?
 
     help_item = items.find { |i| i.type == :help }
     help_item && "Hint: Type `#{help_item.title}` for help"
@@ -54,13 +62,15 @@ def placeholder
 
   private
 
+  def config
+    @config ||= {}
+  end
+
   def omnibar_class
     self.class.name || raise(<<~EOS)
-      RailsOmnibar subclasses must be assigned to constants
-      before configuring or rendering them. E.g.:
+      RailsOmnibar subclasses must be assigned to constants, e.g.:
 
-      Foo = Class.new(RailsOmnibar)
-      Foo.configure { ... }
+      Foo = Class.new(RailsOmnibar).configure { ... }
     EOS
   end
 end
diff --git a/lib/rails_omnibar/inheritance.rb b/lib/rails_omnibar/inheritance.rb
new file mode 100644
index 0000000..510f90d
--- /dev/null
+++ b/lib/rails_omnibar/inheritance.rb
@@ -0,0 +1,9 @@
+class RailsOmnibar
+  def self.inherited(subclass)
+    bar1 = singleton
+    bar2 = subclass.send(:singleton)
+    %i[@commands @config @items].each do |ivar|
+      bar2.instance_variable_set(ivar, bar1.instance_variable_get(ivar).dup)
+    end
+  end
+end
diff --git a/lib/rails_omnibar/item/base.rb b/lib/rails_omnibar/item/base.rb
index bab83e1..adf220e 100644
--- a/lib/rails_omnibar/item/base.rb
+++ b/lib/rails_omnibar/item/base.rb
@@ -1,9 +1,9 @@
 class RailsOmnibar
   module Item
     class Base
-      attr_reader :title, :url, :icon, :modal_html, :suggested, :type
+      attr_reader :title, :url, :icon, :modal_html, :suggested, :type, :if
 
-      def initialize(title:, url: nil, icon: nil, modal_html: nil, suggested: false, type: :default)
+      def initialize(title:, url: nil, icon: nil, modal_html: nil, suggested: false, type: :default, if: nil)
         url.present? && modal_html.present? && raise(ArgumentError, 'use EITHER url: OR modal_html:')
 
         @title      = validate_title(title)
@@ -12,10 +12,16 @@ def initialize(title:, url: nil, icon: nil, modal_html: nil, suggested: false, t
         @modal_html = modal_html
         @suggested  = !!suggested
         @type       = type
+        @if         = RailsOmnibar.cast_to_condition(binding.local_variable_get(:if))
       end
 
       def as_json(*)
-        { title: title, url: url, icon: icon, modalHTML: modal_html, suggested: suggested, type: type }
+        @as_json ||=
+          { title: title, url: url, icon: icon, modalHTML: modal_html, suggested: suggested, type: type }
+      end
+
+      def render?(context:, omnibar:)
+        RailsOmnibar.evaluate_condition(self.if, context: context, omnibar: omnibar)
       end
 
       private
diff --git a/lib/rails_omnibar/items.rb b/lib/rails_omnibar/items.rb
index f939a39..aac8b78 100644
--- a/lib/rails_omnibar/items.rb
+++ b/lib/rails_omnibar/items.rb
@@ -1,13 +1,12 @@
 class RailsOmnibar
   def add_item(item)
-    check_const_and_clear_cache
     items << RailsOmnibar.cast_to_item(item)
-    self
+    self.class
   end
 
   def add_items(*args)
     args.each { |arg| add_item(arg) }
-    self
+    self.class
   end
 
   def self.cast_to_item(arg)
diff --git a/lib/rails_omnibar/rendering.rb b/lib/rails_omnibar/rendering.rb
index f4054bd..74b1190 100644
--- a/lib/rails_omnibar/rendering.rb
+++ b/lib/rails_omnibar/rendering.rb
@@ -1,6 +1,7 @@
 class RailsOmnibar
-  def render
-    @cached_html ||= <<~HTML.html_safe
+  def render(context = nil)
+    @context = context
+    <<~HTML.html_safe
       <script src='#{urls.js_path}?v=#{RailsOmnibar::VERSION}' type='text/javascript'></script>
       <div id='mount-rails-omnibar'>
         <script type="application/json">#{to_json}</script>
@@ -17,9 +18,9 @@ def html_url
   def as_json(*)
     {
       calculator:     calculator?,
-      commandPattern: JsRegex.new!(command_pattern, target: 'ES2018'),
+      commandPattern: command_pattern,
       hotkey:         hotkey,
-      items:          items,
+      items:          items.select { |i| i.render?(context: @context, omnibar: self) },
       maxResults:     max_results,
       modal:          modal?,
       placeholder:    placeholder,
@@ -30,11 +31,4 @@ def as_json(*)
   def urls
     @urls ||= RailsOmnibar::Engine.routes.url_helpers
   end
-
-  private
-
-  def check_const_and_clear_cache
-    omnibar_class # trigger constant assignment check
-    @cached_html = nil
-  end
 end
diff --git a/spec/benchmarks/benchmark.rb b/spec/benchmarks/benchmark.rb
new file mode 100644
index 0000000..c8460f6
--- /dev/null
+++ b/spec/benchmarks/benchmark.rb
@@ -0,0 +1,16 @@
+require_relative '../rails_helper'
+require 'bundler/inline'
+
+gemfile do
+  source 'https://rubygems.org'
+  gem 'benchmark-ips', require: 'benchmark/ips'
+end
+
+BenchmarkBar = Class.new(RailsOmnibar).configure do |c|
+  100.times { c.add_item(title: rand.to_s, url: rand.to_s) }
+  10.times { c.add_command(description: rand.to_s, pattern: /#{rand}/, example: rand.to_s, resolver: ->(_){}) }
+end
+
+Benchmark.ips do |x|
+  x.report('render') { BenchmarkBar.render } # ~3k ips
+end
diff --git a/spec/lib/rails_omnibar/config_spec.rb b/spec/lib/rails_omnibar/config_spec.rb
index bd13b7f..d1f06b8 100644
--- a/spec/lib/rails_omnibar/config_spec.rb
+++ b/spec/lib/rails_omnibar/config_spec.rb
@@ -53,10 +53,8 @@
     expect(subject.placeholder).to eq nil
   end
 
-  it 'raises when trying to configure or render from an anonymous class' do
+  it 'raises when trying to render from an anonymous class' do
     klass = Class.new(RailsOmnibar)
-    expect { klass.configure {} }.to raise_error(/constant/)
-    expect { klass.add_item(title: 'a', url: 'b') }.to raise_error(/constant/)
     expect { klass.render }.to raise_error(/constant/)
   end
 end
diff --git a/spec/lib/rails_omnibar/inheritance_spec.rb b/spec/lib/rails_omnibar/inheritance_spec.rb
new file mode 100644
index 0000000..c30feeb
--- /dev/null
+++ b/spec/lib/rails_omnibar/inheritance_spec.rb
@@ -0,0 +1,79 @@
+require 'rails_helper'
+
+describe RailsOmnibar do
+  it 'inherits commands from a parent class' do
+    bar1 = Class.new(RailsOmnibar).configure do |c|
+      c.add_command(pattern: /foo1/, resolver: ->(_){})
+    end
+    bar2 = Class.new(bar1).configure do |c|
+      c.add_command(pattern: /foo2/, resolver: ->(_){})
+    end
+    bar3 = Class.new(bar2).configure do |c|
+      c.add_command(pattern: /foo3/, resolver: ->(_){})
+    end
+
+    commands = ->(bar) do
+      bar.send(:singleton).send(:commands).map { |c| c.pattern.source }
+    end
+
+    expect(commands.call(bar1)).to eq ['foo1']
+    expect(commands.call(bar2)).to eq ['foo1', 'foo2']
+    expect(commands.call(bar3)).to eq ['foo1', 'foo2', 'foo3']
+
+    # later changes to commands should not affect child classes
+    bar1.add_command(pattern: /foo1B/, resolver: ->(_){})
+    expect(commands.call(bar1)).to eq ['foo1', 'foo1B']
+    expect(commands.call(bar2)).to eq ['foo1', 'foo2']
+    expect(commands.call(bar3)).to eq ['foo1', 'foo2', 'foo3']
+  end
+
+  it 'inherits configuration from a parent class' do
+    bar1 = Class.new(RailsOmnibar).configure do |c|
+      c.max_results = 7
+      c.placeholder = 'hi'
+      c.hotkey = 'j'
+    end
+    bar2 = Class.new(bar1).configure do |c|
+      c.max_results = 8
+    end
+    bar3 = Class.new(bar2).configure do |c|
+      c.hotkey = 'k'
+    end
+
+    config = ->(bar) { bar.send(:singleton).send(:config) }
+
+    expect(config.call(bar1)).to eq(max_results: 7, placeholder: 'hi', hotkey: 'j')
+    expect(config.call(bar2)).to eq(max_results: 8, placeholder: 'hi', hotkey: 'j')
+    expect(config.call(bar3)).to eq(max_results: 8, placeholder: 'hi', hotkey: 'k')
+
+    # later changes to config should not affect child classes
+    bar1.placeholder = 'bye'
+    expect(bar1.placeholder).to eq 'bye'
+    expect(bar2.placeholder).to eq 'hi'
+    expect(bar3.placeholder).to eq 'hi'
+  end
+
+  it 'inherits items from a parent class' do
+    bar1 = Class.new(RailsOmnibar).configure do |c|
+      c.add_item(title: 'foo1', url: 'bar1')
+    end
+    bar2 = Class.new(bar1).configure do |c|
+      c.add_item(title: 'foo2', url: 'bar2')
+    end
+    bar3 = Class.new(bar2).configure do |c|
+      c.add_item(title: 'foo3', url: 'bar3')
+    end
+
+    items = ->(bar) { bar.send(:singleton).send(:items).map(&:title) }
+
+    expect(items.call(bar1)).to eq ['foo1']
+    expect(items.call(bar2)).to eq ['foo1', 'foo2']
+    expect(items.call(bar3)).to eq ['foo1', 'foo2', 'foo3']
+
+    # later changes to items should not affect child classes
+    bar1.add_item(title: 'foo1B', url: 'bar1B')
+    expect(items.call(bar1)).to eq ['foo1', 'foo1B']
+    expect(items.call(bar2)).to eq ['foo1', 'foo2']
+    expect(items.call(bar3)).to eq ['foo1', 'foo2', 'foo3']
+  end
+end
diff --git a/spec/system/rails_omnibar_spec.rb b/spec/system/rails_omnibar_spec.rb
index 1387061..dfac2fe 100644
--- a/spec/system/rails_omnibar_spec.rb
+++ b/spec/system/rails_omnibar_spec.rb
@@ -119,6 +119,33 @@
     expect(page).not_to have_content 'fake_result_1'
   end
 
+  it 'can have conditional items and commands' do
+    visit main_app.root_path
+    send_keys([:control, 'm']) # custom hotkey, c.f. my_omnibar_template.rb
+    expect(page).to have_selector 'input'
+
+    type('condi')
+    expect(page).not_to have_content 'conditional item'
+
+    FactoryBot.create(:user)
+    expect { type('DELETE users'); sleep 0.3 }.not_to change { User.count }
+
+    # now again with truthy condition
+    ENV['FAKE_OMNIBAR_IF'] = '1'
+    refresh # reload page
+
+    send_keys([:control, 'm']) # custom hotkey, c.f. my_omnibar_template.rb
+    expect(page).to have_selector 'input'
+
+    type('condi')
+    expect(page).to have_content 'conditional item'
+
+    FactoryBot.create(:user)
+    expect { type('DELETE users'); sleep 0.3 }.to change { User.count }.to(0)
+  ensure
+    ENV['FAKE_OMNIBAR_IF'] = nil
+  end
+
   def type(str)
     find('input').set(str)
   end
diff --git a/spec/templates/app_template.rb b/spec/templates/app_template.rb
index 0d0641b..b66074d 100644
--- a/spec/templates/app_template.rb
+++ b/spec/templates/app_template.rb
@@ -29,7 +29,7 @@
 
 inject_into_class 'app/controllers/application_controller.rb', 'ApplicationController', <<-RUBY
   def index
-    render html: (MyOmnibar.render + OtherOmnibar.render)
+    render html: (MyOmnibar.render(self) + OtherOmnibar.render(self))
   end
 RUBY
 
diff --git a/spec/templates/my_omnibar_template.rb b/spec/templates/my_omnibar_template.rb
index e9dcdb5..b8772e6 100644
--- a/spec/templates/my_omnibar_template.rb
+++ b/spec/templates/my_omnibar_template.rb
@@ -3,6 +3,7 @@
 
   c.add_item(title: 'important URL', url: 'https://www.disney.com', suggested: true)
   c.add_item(title: 'boring URL', url: 'https://www.github.com')
+  c.add_item(title: 'conditional item', url: '#', if: -> { ENV['FAKE_OMNIBAR_IF'] })
 
   c.add_webadmin_items(prefix: 'Admin:')
 
@@ -43,6 +44,13 @@
     end,
   )
 
+  c.add_command(
+    description: 'Delete users',
+    pattern:     /DELETE (.+)/i,
+    resolver:    ->(value){ { title: value.classify.constantize.delete_all.to_s } },
+    if:          ->{ ENV['FAKE_OMNIBAR_IF'] },
+  )
+
   c.add_help
 
   # Use a hotkey that is the same in most keyboard layouts to work around