Add support for multiple results and formats

Author: maxim

CHANGELOG.md

@@ -1,5 +1,7 @@
 ## [Unreleased]
 
+- Add support for multi-result responses of any formats
+
 ## [0.1.0] - 2025-05-26
 
 - Initial release

Gemfile.lock

@@ -0,0 +1,42 @@
+PATH
+  remote: .
+  specs:
+    tiny_mcp (0.2.0)
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    date (3.4.1)
+    erb (5.0.1)
+    io-console (0.8.0)
+    irb (1.15.2)
+      pp (>= 0.6.0)
+      rdoc (>= 4.0.0)
+      reline (>= 0.4.2)
+    minitest (5.25.5)
+    pp (0.6.2)
+      prettyprint
+    prettyprint (0.2.0)
+    psych (5.2.6)
+      date
+      stringio
+    rake (13.3.0)
+    rdoc (6.14.0)
+      erb
+      psych (>= 4.0.0)
+    reline (0.6.1)
+      io-console (~> 0.5)
+    stringio (3.1.7)
+
+PLATFORMS
+  arm64-darwin-24
+  ruby
+
+DEPENDENCIES
+  irb
+  minitest (~> 5.16)
+  rake (~> 13.0)
+  tiny_mcp!
+
+BUNDLED WITH
+   2.6.9

README.md

@@ -34,7 +34,7 @@ class TimeTool < TinyMCP::Tool
   opt :timezone, :string, 'Timezone name'
 
   def call(timezone: 'UTC')
-    Time.now.getlocal(timezone).to_s
+    Time.now.getlocal(timezone)
   end
 end
 
@@ -56,6 +56,40 @@ claude mcp add my-mcp bin/mcp
 
 The server reads JSON-RPC requests from stdin and writes responses to stdout.
 
+## Multiple results and different formats
+
+By default TinyMCP assumes you're returning `text` from your call function. If you want to return image, audio, or a bunch of different results, wrap your return value in an array, and TinyMCP will treat your return value as the whole `content` body.
+
+Don't forget that binary data such as images and audio needs to be Base64-encoded.
+
+```ruby
+require 'base64'
+
+class MultiModalTool < TinyMCP::Tool
+  name 'get_different_formats'
+  desc 'Get results in different formats'
+
+  def call
+    [
+      {
+        type: 'text',
+        data: 'This is a text response'
+      },
+      {
+        type: 'image',
+        mimeType: 'image/png',
+        data: Base64.strict_encode64(File.read('image.png', 'rb'))
+      },
+      {
+        type: 'audio',
+        mimeType: 'audio/mpeg',
+        data: Base64.strict_encode64(File.read('audio.mp3', 'rb'))
+      }
+    ]
+  end
+end
+```
+
 ## Development
 
 After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake test` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.

lib/tiny_mcp.rb

@@ -108,15 +108,17 @@ def handle_tool_call(request)
       tool = @tools.find { _1.class.mcp.name == name }
 
       if !tool
-        return error_for(request, :invalid_params, "Unknown_tool: #{name}")
+        return error_for(request, :invalid_params, "Unknown tool: #{name}")
       end
 
       args = request.dig('params', 'arguments')&.transform_keys(&:to_sym)
 
       begin
         result = tool.call(**args)
-        # TODO: Support other content types (ask claude code which ones).
-        response_for(request, content: [{ type: 'text', text: result.to_s }])
+
+        result.is_a?(Array) ?
+          response_for(request, content: result) :
+          response_for(request, content: [{ type: 'text', text: result.to_s }])
       rescue => e
         error_for(request, :internal, e.full_message(highlight: false))
       end

test/test_tiny_mcp.rb renamed to test/tiny_mcp_test.rb

@@ -3,7 +3,7 @@
 require 'test_helper'
 require 'stringio'
 
-class TestTinyMCP < Minitest::Test
+class TinyMCPTest < Minitest::Test
   def test_that_it_has_a_version_number
     refute_nil ::TinyMCP::VERSION
   end
@@ -274,7 +274,7 @@ def test_tools_call_nonexistent_tool
 
     assert response[:error]
     assert_equal(-32602, response[:error][:code])
-    assert_match(/Unknown_tool: nonexistent/, response[:error][:message])
+    assert_match(/Unknown tool: nonexistent/, response[:error][:message])
   end
 
   def test_tools_call_with_error
@@ -337,7 +337,8 @@ def test_error_types
 
   def test_error_with_custom_message
     server = TinyMCP::Server.new
-    error = server.send(:error_for, { 'id' => 1 }, :internal, 'Custom error message')
+    error =
+      server.send(:error_for, { 'id' => 1 }, :internal, 'Custom error message')
 
     assert_equal(-32603, error[:error][:code])
     assert_equal 'Custom error message', error[:error][:message]
@@ -501,4 +502,169 @@ def call(test_param:)
     response = server.send(:handle_request, request)
     assert_equal 'Received: value', response[:result][:content][0][:text]
   end
+
+  # Multi-modal Content Tests
+  def test_tool_returning_array_of_content_items
+    multi_content_tool_class = Class.new(TinyMCP::Tool) do
+      name 'multi_content'
+      desc 'Returns multiple content items'
+      arg :content_type, :string, 'Type of content to return'
+
+      def call(content_type:)
+        case content_type
+        when 'multiple_text'
+          [
+            { type: 'text', text: 'First text item' },
+            { type: 'text', text: 'Second text item' },
+            { type: 'text', text: 'Third text item' }
+          ]
+        when 'mixed'
+          [
+            { type: 'text', text: 'Some text content' },
+            { type: 'image',
+              data: 'base64-encoded-image-data',
+              mimeType: 'image/png' },
+            { type: 'text', text: 'More text after image' }
+          ]
+        end
+      end
+    end
+
+    server = TinyMCP::Server.new(multi_content_tool_class)
+    
+    # Test multiple text content
+    request = {
+      'jsonrpc' => '2.0',
+      'id' => 1,
+      'method' => 'tools/call',
+      'params' => {
+        'name' => 'multi_content',
+        'arguments' => { 'content_type' => 'multiple_text' }
+      }
+    }
+
+    response = server.send(:handle_request, request)
+    content = response[:result][:content]
+    
+    assert_equal 3, content.length
+    assert_equal 'First text item', content[0][:text]
+    assert_equal 'Second text item', content[1][:text]
+    assert_equal 'Third text item', content[2][:text]
+    content.each { |item| assert_equal 'text', item[:type] }
+  end
+
+  def test_tool_returning_mixed_content_types
+    mixed_tool_class = Class.new(TinyMCP::Tool) do
+      name 'mixed_content'
+      desc 'Returns mixed content types'
+
+      def call
+        [
+          { type: 'text', text: 'Here is some text' },
+          { type: 'image',
+            mimeType: 'image/png',
+            data: 'iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42' \
+            'mP8/5+hHgAHggJ/PchI7wAAAABJRU5ErkJggg==' },
+          { type: 'text', text: 'And more text after the image' },
+          { type: 'resource',
+            uri: 'file:///path/to/resource.txt',
+            text: 'Resource reference' }
+        ]
+      end
+    end
+
+    server = TinyMCP::Server.new(mixed_tool_class)
+    request = {
+      'jsonrpc' => '2.0',
+      'id' => 1,
+      'method' => 'tools/call',
+      'params' => {
+        'name' => 'mixed_content',
+        'arguments' => {}
+      }
+    }
+
+    response = server.send(:handle_request, request)
+    content = response[:result][:content]
+    
+    assert_equal 4, content.length
+    
+    # Check text content
+    assert_equal 'text', content[0][:type]
+    assert_equal 'Here is some text', content[0][:text]
+    
+    # Check image content
+    assert_equal 'image', content[1][:type]
+    assert_equal 'image/png', content[1][:mimeType]
+    assert_equal 'iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42' \
+                 'mP8/5+hHgAHggJ/PchI7wAAAABJRU5ErkJggg==',
+                 content[1][:data]
+    
+    # Check second text content
+    assert_equal 'text', content[2][:type]
+    assert_equal 'And more text after the image', content[2][:text]
+    
+    # Check resource content
+    assert_equal 'resource', content[3][:type]
+    assert_equal 'file:///path/to/resource.txt', content[3][:uri]
+    assert_equal 'Resource reference', content[3][:text]
+  end
+
+  def test_tool_returning_empty_array
+    empty_tool_class = Class.new(TinyMCP::Tool) do
+      name 'empty_content'
+      desc 'Returns empty content array'
+
+      def call
+        []
+      end
+    end
+
+    server = TinyMCP::Server.new(empty_tool_class)
+    request = {
+      'jsonrpc' => '2.0',
+      'id' => 1,
+      'method' => 'tools/call',
+      'params' => {
+        'name' => 'empty_content',
+        'arguments' => {}
+      }
+    }
+
+    response = server.send(:handle_request, request)
+    content = response[:result][:content]
+    
+    assert_equal [], content
+    assert_equal 0, content.length
+  end
+
+  def test_tool_returning_single_item_array
+    single_tool_class = Class.new(TinyMCP::Tool) do
+      name 'single_content'
+      desc 'Returns single content item in array'
+      arg :message, :string, 'Message to return'
+
+      def call(message:)
+        [{ type: 'text', text: message }]
+      end
+    end
+
+    server = TinyMCP::Server.new(single_tool_class)
+    request = {
+      'jsonrpc' => '2.0',
+      'id' => 1,
+      'method' => 'tools/call',
+      'params' => {
+        'name' => 'single_content',
+        'arguments' => { 'message' => 'Single item message' }
+      }
+    }
+
+    response = server.send(:handle_request, request)
+    content = response[:result][:content]
+    
+    assert_equal 1, content.length
+    assert_equal 'text', content[0][:type]
+    assert_equal 'Single item message', content[0][:text]
+  end
 end