Support Ruby 2.7 - Ruby 3.1

koic · koic · commit aa8bbad491ce · 2026-01-06T10:38:56.000+09:00
## Summary

Unlike applications, libraries provide value by remaining usable for a broad range of users,
even when that means supporting older Ruby versions beyond Ruby's own EOL timeline.

I maintain RuboCop, a Ruby linter. Because linters need to work across the ecosystem,
they often need to keep compatibility with older Ruby versions to some extent.

The trade-off is that the MCP Ruby SDK must remain compatible with Ruby 2.7.
However, given the ecosystem impact, supporting Ruby 2.7 is still worthwhile.

For example, bundled gems such as `csv` (Ruby &gt;= 2.5), `bigdecimal` (Ruby &gt;= 2.5), `json` (Ruby &gt;= 2.7),
and `language_server-protocol` (Ruby &gt;= 2.5) tend to keep compatibility with older Ruby versions.

Unlike dropping support, which imposes restrictions on users,
this change broadens compatibility and does not introduce breaking changes.

## Development Note

`rubocop-shopify` (2.18) supports Ruby 3.1+, and this PR does not change that.
Since RuboCop can configure the runtime Ruby version and the target Ruby version for analysis independently,
CI continues to run RuboCop on Ruby 4.0, while analyzing code with `TargetRubyVersion: 2.7`.

When setting `TargetRubyVersion: 2.7`, several RuboCop offenses were resolved.

Additionally, Sorbet-related libraries support Ruby 3.0+. Since these are not dependencies of the MCP Ruby SDK itself,
they are versioned and tested in the development Gemfile.
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
@@ -7,6 +7,9 @@ jobs:
     strategy:
       matrix:
         entry:
+          - { ruby: '2.7', allowed-failure: false }
+          - { ruby: '3.0', allowed-failure: false }
+          - { ruby: '3.1', allowed-failure: false }
           - { ruby: '3.2', allowed-failure: false }
           - { ruby: '3.3', allowed-failure: false }
           - { ruby: '3.4', allowed-failure: false }
@@ -29,7 +32,7 @@ jobs:
       - uses: actions/checkout@v6
       - uses: ruby/setup-ruby@v1
         with:
-          ruby-version: 3.2 # Specify the oldest supported Ruby version.
+          ruby-version: 4.0 # Specify the latest supported Ruby version.
           bundler-cache: true
       - run: bundle exec rake rubocop
 
@@ -40,6 +43,6 @@ jobs:
       - uses: actions/checkout@v6
       - uses: ruby/setup-ruby@v1
         with:
-          ruby-version: 3.2 # Specify the oldest supported Ruby version.
+          ruby-version: 4.0 # Specify the latest supported Ruby version.
           bundler-cache: true
       - run: bundle exec yard --no-output
diff --git a/.rubocop.yml b/.rubocop.yml
@@ -5,6 +5,9 @@ plugins:
   - rubocop-minitest
   - rubocop-rake
 
+AllCops:
+  TargetRubyVersion: 2.7
+
 Gemspec/DevelopmentDependencies:
   Enabled: true
 
diff --git a/AGENTS.md b/AGENTS.md
@@ -6,7 +6,7 @@ This is the official Ruby SDK for the Model Context Protocol (MCP), implementing
 
 ## Dev environment setup
 
-- Ruby 3.2.0+ required
+- Ruby 3.2.0+ required to run the full test suite, including all Sorbet-related features
 - Run `bundle install` to install dependencies
 - Dependencies: `json-schema` >= 4.1 - Schema validation
 
diff --git a/Gemfile b/Gemfile
@@ -8,17 +8,18 @@ gemspec
 # Specify development dependencies below
 gem "rubocop-minitest", require: false
 gem "rubocop-rake", require: false
-gem "rubocop-shopify", require: false
+gem "rubocop-shopify", ">= 2.18", require: false if RUBY_VERSION >= "3.1"
 
 gem "puma", ">= 5.0.0"
 gem "rackup", ">= 2.1.0"
 
 gem "activesupport"
-gem "debug"
+# Fix io-console install error when Ruby 3.0.
+gem "debug" if RUBY_VERSION >= "3.1"
 gem "rake", "~> 13.0"
-gem "sorbet-static-and-runtime"
+gem "sorbet-static-and-runtime" if RUBY_VERSION >= "3.0"
 gem "yard", "~> 0.9"
-gem "yard-sorbet", "~> 0.9"
+gem "yard-sorbet", "~> 0.9" if RUBY_VERSION >= "3.1"
 
 group :test do
   gem "faraday", ">= 2.0"
diff --git a/lib/json_rpc_handler.rb b/lib/json_rpc_handler.rb
@@ -22,14 +22,14 @@ class ErrorCode
 
   def handle(request, id_validation_pattern: DEFAULT_ALLOWED_ID_CHARACTERS, &method_finder)
     if request.is_a?(Array)
-      return error_response(id: :unknown_id, id_validation_pattern:, error: {
+      return error_response(id: :unknown_id, id_validation_pattern: id_validation_pattern, error: {
         code: ErrorCode::INVALID_REQUEST,
         message: "Invalid Request",
         data: "Request is an empty array",
       }) if request.empty?
 
       # Handle batch requests
-      responses = request.map { |req| process_request(req, id_validation_pattern:, &method_finder) }.compact
+      responses = request.map { |req| process_request(req, id_validation_pattern: id_validation_pattern, &method_finder) }.compact
 
       # A single item is hoisted out of the array
       return responses.first if responses.one?
@@ -38,9 +38,9 @@ def handle(request, id_validation_pattern: DEFAULT_ALLOWED_ID_CHARACTERS, &metho
       responses if responses.any?
     elsif request.is_a?(Hash)
       # Handle single request
-      process_request(request, id_validation_pattern:, &method_finder)
+      process_request(request, id_validation_pattern: id_validation_pattern, &method_finder)
     else
-      error_response(id: :unknown_id, id_validation_pattern:, error: {
+      error_response(id: :unknown_id, id_validation_pattern: id_validation_pattern, error: {
         code: ErrorCode::INVALID_REQUEST,
         message: "Invalid Request",
         data: "Request must be an array or a hash",
@@ -51,9 +51,9 @@ def handle(request, id_validation_pattern: DEFAULT_ALLOWED_ID_CHARACTERS, &metho
   def handle_json(request_json, id_validation_pattern: DEFAULT_ALLOWED_ID_CHARACTERS, &method_finder)
     begin
       request = JSON.parse(request_json, symbolize_names: true)
-      response = handle(request, id_validation_pattern:, &method_finder)
+      response = handle(request, id_validation_pattern: id_validation_pattern, &method_finder)
     rescue JSON::ParserError
-      response = error_response(id: :unknown_id, id_validation_pattern:, error: {
+      response = error_response(id: :unknown_id, id_validation_pattern: id_validation_pattern, error: {
         code: ErrorCode::PARSE_ERROR,
         message: "Parse error",
         data: "Invalid JSON",
@@ -74,7 +74,7 @@ def process_request(request, id_validation_pattern:, &method_finder)
       'Method name must be a string and not start with "rpc."'
     end
 
-    return error_response(id: :unknown_id, id_validation_pattern:, error: {
+    return error_response(id: :unknown_id, id_validation_pattern: id_validation_pattern, error: {
       code: ErrorCode::INVALID_REQUEST,
       message: "Invalid Request",
       data: error,
@@ -84,7 +84,7 @@ def process_request(request, id_validation_pattern:, &method_finder)
     params = request[:params]
 
     unless valid_params?(params)
-      return error_response(id:, id_validation_pattern:, error: {
+      return error_response(id: id, id_validation_pattern: id_validation_pattern, error: {
         code: ErrorCode::INVALID_PARAMS,
         message: "Invalid params",
         data: "Method parameters must be an array or an object or null",
@@ -95,7 +95,7 @@ def process_request(request, id_validation_pattern:, &method_finder)
       method = method_finder.call(method_name)
 
       if method.nil?
-        return error_response(id:, id_validation_pattern:, error: {
+        return error_response(id: id, id_validation_pattern: id_validation_pattern, error: {
           code: ErrorCode::METHOD_NOT_FOUND,
           message: "Method not found",
           data: method_name,
@@ -104,9 +104,9 @@ def process_request(request, id_validation_pattern:, &method_finder)
 
       result = method.call(params)
 
-      success_response(id:, result:)
+      success_response(id: id, result: result)
     rescue StandardError => e
-      error_response(id:, id_validation_pattern:, error: {
+      error_response(id: id, id_validation_pattern: id_validation_pattern, error: {
         code: ErrorCode::INTERNAL_ERROR,
         message: "Internal error",
         data: e.message,
@@ -136,8 +136,8 @@ def valid_params?(params)
   def success_response(id:, result:)
     {
       jsonrpc: Version::V2_0,
-      id:,
-      result:,
+      id: id,
+      result: result,
     } unless id.nil?
   end
 
diff --git a/lib/mcp/client/http.rb b/lib/mcp/client/http.rb
@@ -18,42 +18,42 @@ def send_request(request:)
       rescue Faraday::BadRequestError => e
         raise RequestHandlerError.new(
           "The #{method} request is invalid",
-          { method:, params: },
+          { method: method, params: params },
           error_type: :bad_request,
           original_error: e,
         )
       rescue Faraday::UnauthorizedError => e
         raise RequestHandlerError.new(
           "You are unauthorized to make #{method} requests",
-          { method:, params: },
+          { method: method, params: params },
           error_type: :unauthorized,
           original_error: e,
         )
       rescue Faraday::ForbiddenError => e
         raise RequestHandlerError.new(
           "You are forbidden to make #{method} requests",
-          { method:, params: },
+          { method: method, params: params },
           error_type: :forbidden,
           original_error: e,
         )
       rescue Faraday::ResourceNotFound => e
         raise RequestHandlerError.new(
           "The #{method} request is not found",
-          { method:, params: },
+          { method: method, params: params },
           error_type: :not_found,
           original_error: e,
         )
       rescue Faraday::UnprocessableEntityError => e
         raise RequestHandlerError.new(
           "The #{method} request is unprocessable",
-          { method:, params: },
+          { method: method, params: params },
           error_type: :unprocessable_entity,
           original_error: e,
         )
       rescue Faraday::Error => e # Catch-all
         raise RequestHandlerError.new(
           "Internal error handling #{method} request",
-          { method:, params: },
+          { method: method, params: params },
           error_type: :internal_error,
           original_error: e,
         )
diff --git a/lib/mcp/configuration.rb b/lib/mcp/configuration.rb
@@ -85,10 +85,10 @@ def merge(other)
       validate_tool_call_arguments = other.validate_tool_call_arguments
 
       Configuration.new(
-        exception_reporter:,
-        instrumentation_callback:,
-        protocol_version:,
-        validate_tool_call_arguments:,
+        exception_reporter: exception_reporter,
+        instrumentation_callback: instrumentation_callback,
+        protocol_version: protocol_version,
+        validate_tool_call_arguments: validate_tool_call_arguments,
       )
     end
 
diff --git a/lib/mcp/content.rb b/lib/mcp/content.rb
@@ -11,7 +11,7 @@ def initialize(text, annotations: nil)
       end
 
       def to_h
-        { text:, annotations:, type: "text" }.compact
+        { text: text, annotations: annotations, type: "text" }.compact
       end
     end
 
@@ -25,7 +25,7 @@ def initialize(data, mime_type, annotations: nil)
       end
 
       def to_h
-        { data:, mime_type:, annotations:, type: "image" }.compact
+        { data: data, mime_type: mime_type, annotations: annotations, type: "image" }.compact
       end
     end
   end
diff --git a/lib/mcp/instrumentation.rb b/lib/mcp/instrumentation.rb
@@ -6,7 +6,7 @@ def instrument_call(method, &block)
       start_time = Process.clock_gettime(Process::CLOCK_MONOTONIC)
       begin
         @instrumentation_data = {}
-        add_instrumentation_data(method:)
+        add_instrumentation_data(method: method)
 
         result = yield block
 
diff --git a/lib/mcp/prompt.rb b/lib/mcp/prompt.rb
@@ -96,7 +96,7 @@ def define(name: nil, title: nil, description: nil, icons: [], arguments: [], me
           icons icons
           arguments arguments
           define_singleton_method(:template) do |args, server_context: nil|
-            instance_exec(args, server_context:, &block)
+            instance_exec(args, server_context: server_context, &block)
           end
           meta meta
         end
diff --git a/lib/mcp/prompt/message.rb b/lib/mcp/prompt/message.rb
@@ -11,7 +11,7 @@ def initialize(role:, content:)
       end
 
       def to_h
-        { role:, content: content.to_h }.compact
+        { role: role, content: content.to_h }.compact
       end
     end
   end
diff --git a/lib/mcp/prompt/result.rb b/lib/mcp/prompt/result.rb
@@ -11,7 +11,7 @@ def initialize(description: nil, messages: [])
       end
 
       def to_h
-        { description:, messages: messages.map(&:to_h) }.compact
+        { description: description, messages: messages.map(&:to_h) }.compact
       end
     end
   end
diff --git a/lib/mcp/resource/contents.rb b/lib/mcp/resource/contents.rb
@@ -11,7 +11,7 @@ def initialize(uri:, mime_type: nil)
       end
 
       def to_h
-        { uri:, mime_type: }.compact
+        { uri: uri, mime_type: mime_type }.compact
       end
     end
 
diff --git a/lib/mcp/resource/embedded.rb b/lib/mcp/resource/embedded.rb
@@ -10,7 +10,7 @@ def initialize(resource:, annotations: nil)
       end
 
       def to_h
-        { resource: resource.to_h, annotations: }.compact
+        { resource: resource.to_h, annotations: annotations }.compact
       end
     end
   end
diff --git a/lib/mcp/server.rb b/lib/mcp/server.rb
@@ -114,7 +114,7 @@ def handle_json(request)
     end
 
     def define_tool(name: nil, title: nil, description: nil, input_schema: nil, annotations: nil, meta: nil, &block)
-      tool = Tool.define(name:, title:, description:, input_schema:, annotations:, meta:, &block)
+      tool = Tool.define(name: name, title: title, description: description, input_schema: input_schema, annotations: annotations, meta: meta, &block)
       tool_name = tool.name_value
 
       @tool_names << tool_name
@@ -124,7 +124,7 @@ def define_tool(name: nil, title: nil, description: nil, input_schema: nil, anno
     end
 
     def define_prompt(name: nil, title: nil, description: nil, arguments: [], &block)
-      prompt = Prompt.define(name:, title:, description:, arguments:, &block)
+      prompt = Prompt.define(name: name, title: title, description: description, arguments: arguments, &block)
       @prompts[prompt.name_value] = prompt
 
       validate!
@@ -289,11 +289,11 @@ def default_capabilities
 
     def server_info
       @server_info ||= {
-        description:,
-        icons:,
-        name:,
-        title:,
-        version:,
+        description: description,
+        icons: icons,
+        name: name,
+        title: title,
+        version: version,
         websiteUrl: website_url,
       }.compact
     end
@@ -316,13 +316,13 @@ def call_tool(request)
 
       tool = tools[tool_name]
       unless tool
-        add_instrumentation_data(tool_name:, error: :tool_not_found)
+        add_instrumentation_data(tool_name: tool_name, error: :tool_not_found)
 
         return error_tool_response("Tool not found: #{tool_name}")
       end
 
       arguments = request[:arguments] || {}
-      add_instrumentation_data(tool_name:)
+      add_instrumentation_data(tool_name: tool_name)
 
       if tool.input_schema&.missing_required_arguments?(arguments)
         add_instrumentation_data(error: :missing_required_arguments)
@@ -360,7 +360,7 @@ def get_prompt(request)
         raise RequestHandlerError.new("Prompt not found #{prompt_name}", request, error_type: :prompt_not_found)
       end
 
-      add_instrumentation_data(prompt_name:)
+      add_instrumentation_data(prompt_name: prompt_name)
 
       prompt_args = request[:arguments]
       prompt.validate_arguments!(prompt_args)
diff --git a/lib/mcp/server/transports/streamable_http_transport.rb b/lib/mcp/server/transports/streamable_http_transport.rb
@@ -42,7 +42,7 @@ def send_notification(method, params = nil, session_id: nil)
 
           notification = {
             jsonrpc: "2.0",
-            method:,
+            method: method,
           }
           notification[:params] = params if params
 
diff --git a/lib/mcp/tool/annotations.rb b/lib/mcp/tool/annotations.rb
@@ -19,7 +19,7 @@ def to_h
           idempotentHint: idempotent_hint,
           openWorldHint: open_world_hint,
           readOnlyHint: read_only_hint,
-          title:,
+          title: title,
         }.compact
       end
     end
diff --git a/lib/mcp/tool/response.rb b/lib/mcp/tool/response.rb
@@ -23,7 +23,7 @@ def error?
       end
 
       def to_h
-        { content:, isError: error?, structuredContent: @structured_content }.compact
+        { content: content, isError: error?, structuredContent: @structured_content }.compact
       end
     end
   end
diff --git a/mcp.gemspec b/mcp.gemspec
@@ -13,7 +13,8 @@ Gem::Specification.new do |spec|
   spec.homepage      = "https://github.com/modelcontextprotocol/ruby-sdk"
   spec.license       = "MIT"
 
-  spec.required_ruby_version = ">= 3.2.0"
+  # Since this library is used by a broad range of users, it does not align its support policy with Ruby's EOL.
+  spec.required_ruby_version = ">= 2.7.0"
 
   spec.metadata["allowed_push_host"] = "https://rubygems.org"
   spec.metadata["changelog_uri"] = "https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v#{spec.version}"
diff --git a/test/json_rpc_handler_test.rb b/test/json_rpc_handler_test.rb
diff --git a/test/mcp/client_test.rb b/test/mcp/client_test.rb
diff --git a/test/mcp/prompt_test.rb b/test/mcp/prompt_test.rb
diff --git a/test/mcp/server/transports/streamable_http_transport_test.rb b/test/mcp/server/transports/streamable_http_transport_test.rb
diff --git a/test/mcp/server_test.rb b/test/mcp/server_test.rb
diff --git a/test/mcp/tool_test.rb b/test/mcp/tool_test.rb
diff --git a/test/test_helper.rb b/test/test_helper.rb
