diff --git a/enterprise/app/models/captain/custom_tool.rb b/enterprise/app/models/captain/custom_tool.rb
index 6d39c4e1a..8ad02f401 100644
--- a/enterprise/app/models/captain/custom_tool.rb
+++ b/enterprise/app/models/captain/custom_tool.rb
@@ -25,6 +25,7 @@
 #
 class Captain::CustomTool < ApplicationRecord
   include Concerns::Toolable
+  include Concerns::SafeEndpointValidatable
 
   self.table_name = 'captain_custom_tools'
 
diff --git a/enterprise/app/models/concerns/safe_endpoint_validatable.rb b/enterprise/app/models/concerns/safe_endpoint_validatable.rb
new file mode 100644
index 000000000..53c2cfeb7
--- /dev/null
+++ b/enterprise/app/models/concerns/safe_endpoint_validatable.rb
@@ -0,0 +1,81 @@
+module Concerns::SafeEndpointValidatable
+  extend ActiveSupport::Concern
+
+  FRONTEND_HOST = URI.parse(ENV.fetch('FRONTEND_URL', 'http://localhost:3000')).host.freeze
+  DISALLOWED_HOSTS = ['localhost', /\.local\z/i].freeze
+
+  included do
+    validate :validate_safe_endpoint_url
+  end
+
+  private
+
+  def validate_safe_endpoint_url
+    return if endpoint_url.blank?
+
+    uri = parse_endpoint_uri
+    return errors.add(:endpoint_url, 'must be a valid URL') unless uri
+
+    validate_endpoint_scheme(uri)
+    validate_endpoint_host(uri)
+    validate_not_ip_address(uri)
+    validate_no_unicode_chars(uri)
+  end
+
+  def parse_endpoint_uri
+    URI.parse(endpoint_url)
+  rescue URI::InvalidURIError
+    nil
+  end
+
+  def validate_endpoint_scheme(uri)
+    return if uri.scheme == 'https'
+
+    errors.add(:endpoint_url, 'must use HTTPS protocol')
+  end
+
+  def validate_endpoint_host(uri)
+    if uri.host.blank?
+      errors.add(:endpoint_url, 'must have a valid hostname')
+      return
+    end
+
+    if uri.host == FRONTEND_HOST
+      errors.add(:endpoint_url, 'cannot point to the application itself')
+      return
+    end
+
+    DISALLOWED_HOSTS.each do |pattern|
+      matched = if pattern.is_a?(Regexp)
+                  uri.host =~ pattern
+                else
+                  uri.host.downcase == pattern
+                end
+
+      next unless matched
+
+      errors.add(:endpoint_url, 'cannot use disallowed hostname')
+      break
+    end
+  end
+
+  def validate_not_ip_address(uri)
+    # Check for IPv4
+    if /\A\d+\.\d+\.\d+\.\d+\z/.match?(uri.host)
+      errors.add(:endpoint_url, 'cannot be an IP address, must be a hostname')
+      return
+    end
+
+    # Check for IPv6
+    return unless uri.host.include?(':')
+
+    errors.add(:endpoint_url, 'cannot be an IP address, must be a hostname')
+  end
+
+  def validate_no_unicode_chars(uri)
+    return unless uri.host
+    return if /\A[\x00-\x7F]+\z/.match?(uri.host)
+
+    errors.add(:endpoint_url, 'hostname cannot contain non-ASCII characters')
+  end
+end