diff --git a/app/services/aws_service.rb b/app/services/aws_service.rb
index 332b3ec..3fa5997 100644
--- a/app/services/aws_service.rb
+++ b/app/services/aws_service.rb
@@ -3,6 +3,8 @@
 require 'aws-sdk-s3'
 
 class AwsService
+  attr_reader :s3_client, :bucket
+
   class ConfigurationError < StandardError; end
 
   def initialize
diff --git a/sig/aws_service.rbs b/sig/aws_service.rbs
new file mode 100644
index 0000000..2deff53
--- /dev/null
+++ b/sig/aws_service.rbs
@@ -0,0 +1,19 @@
+class AwsService
+  class ConfigurationError < StandardError
+  end
+
+  attr_reader bucket: String
+  attr_reader s3_client: Aws::S3::Client
+
+  def initialize: () -> void
+
+  def upload_stream: (IO io, String key) -> Aws::S3::Types::PutObjectOutput
+
+  def file_exists?: (String key) -> bool
+
+  private
+
+  def credentials: () -> Hash[Symbol, String]
+
+  def validate_credentials!: () -> void
+end