diff --git a/lib/json_rpc_handler.rb b/lib/json_rpc_handler.rb
new file mode 100644
index 0000000..309044e
--- /dev/null
+++ b/lib/json_rpc_handler.rb
@@ -0,0 +1,151 @@
+# frozen_string_literal: true
+
+require "json"
+
+module JsonRpcHandler
+  class Version
+    V1_0 = "1.0"
+    V2_0 = "2.0"
+  end
+
+  class ErrorCode
+    INVALID_REQUEST = -32600
+    METHOD_NOT_FOUND = -32601
+    INVALID_PARAMS = -32602
+    INTERNAL_ERROR = -32603
+    PARSE_ERROR = -32700
+  end
+
+  DEFAULT_ALLOWED_ID_CHARACTERS = /\A[a-zA-Z0-9_-]+\z/
+
+  extend self
+
+  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: {
+        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
+
+      # A single item is hoisted out of the array
+      return responses.first if responses.one?
+
+      # An empty array yields nil
+      responses if responses.any?
+    elsif request.is_a?(Hash)
+      # Handle single request
+      process_request(request, id_validation_pattern:, &method_finder)
+    else
+      error_response(id: :unknown_id, id_validation_pattern:, error: {
+        code: ErrorCode::INVALID_REQUEST,
+        message: "Invalid Request",
+        data: "Request must be an array or a hash",
+      })
+    end
+  end
+
+  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)
+    rescue JSON::ParserError
+      response = error_response(id: :unknown_id, id_validation_pattern:, error: {
+        code: ErrorCode::PARSE_ERROR,
+        message: "Parse error",
+        data: "Invalid JSON",
+      })
+    end
+
+    response&.to_json
+  end
+
+  def process_request(request, id_validation_pattern:, &method_finder)
+    id = request[:id]
+
+    error = if !valid_version?(request[:jsonrpc])
+      "JSON-RPC version must be 2.0"
+    elsif !valid_id?(request[:id], id_validation_pattern)
+      "Request ID must match validation pattern, or be an integer or null"
+    elsif !valid_method_name?(request[:method])
+      'Method name must be a string and not start with "rpc."'
+    end
+
+    return error_response(id: :unknown_id, id_validation_pattern:, error: {
+      code: ErrorCode::INVALID_REQUEST,
+      message: "Invalid Request",
+      data: error,
+    }) if error
+
+    method_name = request[:method]
+    params = request[:params]
+
+    unless valid_params?(params)
+      return error_response(id:, id_validation_pattern:, error: {
+        code: ErrorCode::INVALID_PARAMS,
+        message: "Invalid params",
+        data: "Method parameters must be an array or an object or null",
+      })
+    end
+
+    begin
+      method = method_finder.call(method_name)
+
+      if method.nil?
+        return error_response(id:, id_validation_pattern:, error: {
+          code: ErrorCode::METHOD_NOT_FOUND,
+          message: "Method not found",
+          data: method_name,
+        })
+      end
+
+      result = method.call(params)
+
+      success_response(id:, result:)
+    rescue StandardError => e
+      error_response(id:, id_validation_pattern:, error: {
+        code: ErrorCode::INTERNAL_ERROR,
+        message: "Internal error",
+        data: e.message,
+      })
+    end
+  end
+
+  def valid_version?(version)
+    version == Version::V2_0
+  end
+
+  def valid_id?(id, pattern = nil)
+    return true if id.nil? || id.is_a?(Integer)
+    return false unless id.is_a?(String)
+
+    pattern ? id.match?(pattern) : true
+  end
+
+  def valid_method_name?(method)
+    method.is_a?(String) && !method.start_with?("rpc.")
+  end
+
+  def valid_params?(params)
+    params.nil? || params.is_a?(Array) || params.is_a?(Hash)
+  end
+
+  def success_response(id:, result:)
+    {
+      jsonrpc: Version::V2_0,
+      id:,
+      result:,
+    } unless id.nil?
+  end
+
+  def error_response(id:, id_validation_pattern:, error:)
+    {
+      jsonrpc: Version::V2_0,
+      id: valid_id?(id, id_validation_pattern) ? id : nil,
+      error: error.compact,
+    } unless id.nil?
+  end
+end
diff --git a/lib/mcp.rb b/lib/mcp.rb
index f3e7788..4087bef 100644
--- a/lib/mcp.rb
+++ b/lib/mcp.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require_relative "json_rpc_handler"
 require_relative "mcp/configuration"
 require_relative "mcp/content"
 require_relative "mcp/instrumentation"
diff --git a/lib/mcp/server.rb b/lib/mcp/server.rb
index c9aea19..3a2dd9f 100644
--- a/lib/mcp/server.rb
+++ b/lib/mcp/server.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "json_rpc_handler"
+require_relative "../json_rpc_handler"
 require_relative "instrumentation"
 require_relative "methods"
 
diff --git a/mcp.gemspec b/mcp.gemspec
index b1b77be..57cd60a 100644
--- a/mcp.gemspec
+++ b/mcp.gemspec
@@ -29,6 +29,5 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ["lib"]
 
-  spec.add_dependency("json_rpc_handler", "~> 0.1")
   spec.add_dependency("json-schema", ">= 4.1")
 end
diff --git a/test/json_rpc_handler_test.rb b/test/json_rpc_handler_test.rb
new file mode 100644
index 0000000..38004e6
--- /dev/null
+++ b/test/json_rpc_handler_test.rb
@@ -0,0 +1,663 @@
+# frozen_string_literal: true
+
+require "test_helper"
+
+describe JsonRpcHandler do
+  before do
+    @registry = {}
+    @response = nil
+    @response_json = nil
+  end
+
+  describe "#handle" do
+    # Comments verbatim from https://www.jsonrpc.org/specification
+    #
+    # JSON-RPC 2.0 Specification
+    #
+    # 1 Overview
+    # ...
+    # 2 Conventions
+    # ...
+    # 3 Compatibility
+    # ...
+    # 4 Request object
+    #
+    # A rpc call is represented by sending a Request object to a Server. The Request object has the following members:
+    #
+    # jsonrpc
+    #   A String specifying the version of the JSON-RPC protocol. MUST be exactly "2.0".
+
+    it "returns a result when jsonrpc is 2.0" do
+      register("add") { |params| params[:a] + params[:b] }
+
+      handle jsonrpc: "2.0", id: 1, method: "add", params: { a: 1, b: 2 }
+
+      assert_rpc_success expected_result: 3
+    end
+
+    it "returns an error when jsonrpc is not 2.0" do
+      handle jsonrpc: "3.0", id: 1, method: "add", params: { a: 1, b: 2 }
+
+      assert_rpc_error expected_error: {
+        code: -32600,
+        message: "Invalid Request",
+        data: "JSON-RPC version must be 2.0",
+      }
+    end
+
+    # method
+    #   A String containing the name of the method to be invoked. Method names that begin with the word rpc followed by
+    #   a period character (U+002E or ASCII 46) are reserved for rpc-internal methods and extensions and MUST NOT be
+    #   used for anything else.
+
+    it "returns an error when method is not a string" do
+      handle jsonrpc: "2.0", id: 1, method: 42, params: { a: 1, b: 2 }
+
+      assert_rpc_error expected_error: {
+        code: -32600,
+        message: "Invalid Request",
+        data: 'Method name must be a string and not start with "rpc."',
+      }
+    end
+
+    it "returns an error when method begins with 'rpc.'" do
+      handle jsonrpc: "2.0", id: 1, method: "rpc.add", params: { a: 1, b: 2 }
+
+      assert_rpc_error expected_error: {
+        code: -32600,
+        message: "Invalid Request",
+        data: 'Method name must be a string and not start with "rpc."',
+      }
+    end
+
+    # params
+    #   A Structured value that holds the parameter values to be used during the invocation of the method. This member
+    #   MAY be omitted.
+
+    it "returns a result when parameters are omitted" do
+      register("greet") { "Hello, world!" }
+
+      handle jsonrpc: "2.0", id: 1, method: "greet"
+
+      assert_rpc_success expected_result: "Hello, world!"
+    end
+
+    # id
+    #   An identifier established by the Client that MUST contain a String, Number, or NULL value if included. If it is
+    #   not included it is assumed to be a notification. The value SHOULD normally not be Null and Numbers SHOULD NOT
+    #   contain fractional parts.
+    #
+    #   The Server MUST reply with the same value in the Response object if included. This member is used to correlate the
+    #   context between the two objects.
+
+    it "returns a response with the same request id when the id is a valid string" do
+      register("add") { |params| params[:a] + params[:b] }
+      id = "request-123_abc"
+
+      handle jsonrpc: "2.0", id:, method: "add", params: { a: 1, b: 2 }
+
+      assert_rpc_success expected_result: 3
+      assert_equal id, @response[:id]
+    end
+
+    it "returns a response with the same request id when the id is an integer" do
+      register("add") { |params| params[:a] + params[:b] }
+      id = 42
+
+      handle jsonrpc: "2.0", id:, method: "add", params: { a: 1, b: 2 }
+
+      assert_rpc_success expected_result: 3
+      assert_equal id, @response[:id]
+    end
+
+    it "returns an error when request id is not of a valid type" do
+      handle jsonrpc: "2.0", id: true, method: "add", params: { a: 1, b: 2 }
+
+      assert_rpc_error expected_error: {
+        code: -32600,
+        message: "Invalid Request",
+        data: "Request ID must match validation pattern, or be an integer or null",
+      }
+    end
+
+    it "accepts string id with alphanumerics, dashes, and underscores" do
+      register("add") { |params| params[:a] + params[:b] }
+      id = "request-123_ABC"
+
+      handle jsonrpc: "2.0", id:, method: "add", params: { a: 1, b: 2 }
+
+      assert_rpc_success expected_result: 3
+      assert_equal id, @response[:id]
+    end
+
+    it "accepts UUID format strings" do
+      register("add") { |params| params[:a] + params[:b] }
+      id = "550e8400-e29b-41d4-a716-446655440000"
+
+      handle jsonrpc: "2.0", id:, method: "add", params: { a: 1, b: 2 }
+
+      assert_rpc_success expected_result: 3
+      assert_equal id, @response[:id]
+    end
+
+    it "returns an error when request id contains HTML content (XSS prevention)" do
+      handle jsonrpc: "2.0", id: "<script>alert('xss')</script>", method: "add", params: { a: 1, b: 2 }
+
+      assert_rpc_error expected_error: {
+        code: -32600,
+        message: "Invalid Request",
+        data: "Request ID must match validation pattern, or be an integer or null",
+      }
+    end
+
+    it "returns an error when request id contains spaces" do
+      handle jsonrpc: "2.0", id: "request 123", method: "add", params: { a: 1, b: 2 }
+
+      assert_rpc_error expected_error: {
+        code: -32600,
+        message: "Invalid Request",
+        data: "Request ID must match validation pattern, or be an integer or null",
+      }
+    end
+
+    it "returns an error when request id contains special characters" do
+      handle jsonrpc: "2.0", id: "request@123", method: "add", params: { a: 1, b: 2 }
+
+      assert_rpc_error expected_error: {
+        code: -32600,
+        message: "Invalid Request",
+        data: "Request ID must match validation pattern, or be an integer or null",
+      }
+    end
+
+    it "returns an error when request id is an empty string" do
+      handle jsonrpc: "2.0", id: "", method: "add", params: { a: 1, b: 2 }
+
+      assert_rpc_error expected_error: {
+        code: -32600,
+        message: "Invalid Request",
+        data: "Request ID must match validation pattern, or be an integer or null",
+      }
+    end
+
+    it "returns an error when id is a number with a fractional part" do
+      handle jsonrpc: "2.0", id: 3.14, method: "add", params: { a: 1, b: 2 }
+
+      assert_rpc_error expected_error: {
+        code: -32600,
+        message: "Invalid Request",
+        data: "Request ID must match validation pattern, or be an integer or null",
+      }
+    end
+
+    # 4.1 Notification
+    #
+    # A Notification is a Request object without an "id" member. A Request object that is a Notification signifies the
+    # Client's lack of interest in the corresponding Response object, and as such no Response object needs to be
+    # returned to the client. The Server MUST NOT reply to a Notification, including those that are within a batch
+    # request.
+    #
+    # Notifications are not confirmable by definition, since they do not have a Response object to be returned. As such,
+    # the Client would not be aware of any errors (like e.g. "Invalid params","Internal error").
+
+    describe "with a notification request" do
+      it "returns nil even if the method returns a result" do
+        register("ping") { "pong" }
+
+        handle jsonrpc: "2.0", method: "ping"
+
+        assert_nil @response
+      end
+
+      it "returns nil even if the method raises an error" do
+        register("ping") { raise StandardError, "Something bad happened" }
+
+        handle jsonrpc: "2.0", method: "ping"
+
+        assert_nil @response
+      end
+    end
+
+    # 4.2 Parameter Structures
+    #
+    # If present, parameters for the rpc call MUST be provided as a Structured value. Either by-position through an
+    # Array or by-name through an Object.
+    #
+    # * by-position: params MUST be an Array, containing the values in the Server expected order.
+    # * by-name: params MUST be an Object, with member names that match the Server expected parameter names. The absence
+    #   of expected names MAY result in an error being generated. The names MUST match exactly, including case, to the
+    #   method's expected parameters.
+
+    it "with array params returns a result" do
+      register("sum", &:sum)
+
+      handle jsonrpc: "2.0", id: 1, method: "sum", params: [1, 2, 3]
+
+      assert_rpc_success expected_result: 6
+    end
+
+    it "with hash params returns a result" do
+      register("sum") { |params| params[:a] + params[:b] }
+
+      handle jsonrpc: "2.0", id: 1, method: "sum", params: { a: 1, b: 2 }
+
+      assert_rpc_success expected_result: 3
+    end
+
+    # 5 Response object
+    #
+    # When a rpc call is made, the Server MUST reply with a Response, except for in the case of Notifications. The
+    # Response is expressed as a single JSON Object, with the following members:
+
+    # jsonrpc
+    #   A String specifying the version of the JSON-RPC protocol. MUST be exactly "2.0".
+
+    it "returns a result with jsonrpc set to 2.0" do
+      register("add") { |params| params[:a] + params[:b] }
+
+      handle jsonrpc: "2.0", id: 1, method: "add", params: { a: 1, b: 2 }
+
+      assert_equal "2.0", @response[:jsonrpc]
+    end
+
+    # result
+    #   This member is REQUIRED on success.
+    #   This member MUST NOT exist if there was an error invoking the method.
+    #   The value of this member is determined by the method invoked on the Server.
+    #
+    # error
+    #   This member is REQUIRED on error.
+    #   This member MUST NOT exist if there was no error triggered during invocation.
+    #   The value for this member MUST be an Object as defined in section 5.1.
+    #
+    # id
+    #   This member is REQUIRED.
+    #   It MUST be the same as the value of the id member in the Request Object.
+    #   If there was an error in detecting the id in the Request object (e.g. Parse error/Invalid Request), it MUST be
+    #   Null.
+    #
+    # Either the result member or error member MUST be included, but both members MUST NOT be included.
+
+    it "returns a result object and no error object on success" do
+      register("ping") { "pong" }
+
+      handle jsonrpc: "2.0", id: 1, method: "ping"
+
+      assert_rpc_success expected_result: "pong"
+      assert_equal 1, @response[:id]
+      assert_nil @response[:error]
+    end
+
+    it "returns an error object and no result object on error" do
+      register("ping") { raise StandardError, "Something bad happened" }
+
+      handle jsonrpc: "2.0", id: 1, method: "ping"
+
+      assert_rpc_error expected_error: {
+        code: -32603,
+        message: "Internal error",
+        data: "Something bad happened",
+      }
+      assert_equal 1, @response[:id]
+      assert_nil @response[:result]
+    end
+
+    it "returns nil for id when there is an error and and error detecting the id" do
+      register("ping") { "pong" }
+
+      handle jsonrpc: "2.0", id: {}, method: "ping"
+
+      assert_rpc_error expected_error: {
+        code: -32600,
+        message: "Invalid Request",
+        data: "Request ID must match validation pattern, or be an integer or null",
+      }
+      assert_nil @response[:id]
+    end
+
+    # 5.1 Error object
+    #
+    # When a rpc call encounters an error, the Response Object MUST contain the error member with a value that is a
+    # Object with the following members:
+    #
+    # code
+    #   A Number that indicates the error type that occurred.
+    #   This MUST be an integer.
+    # message
+    #   A String providing a short description of the error.
+    #   The message SHOULD be limited to a concise single sentence.
+    # data
+    #   A Primitive or Structured value that contains additional information about the error.
+    #   This may be omitted.
+    #   The value of this member is defined by the Server (e.g. detailed error information, nested errors etc.).
+    #
+    # | code   | message          | meaning                                       |
+    # | ------ | ---------------- | --------------------------------------------- |
+    # | -32700 | Parse error      | Invalid JSON was received by the server.      |
+    # | -32600 | Invalid Request  | The JSON sent is not a valid Request object.  |
+    # | -32601 | Method not found | The method does not exist / is not available. |
+    # | -32602 | Invalid params   | Invalid method parameter(s).                  |
+    # | -32603 | Internal error   | Internal JSON-RPC error.                      |
+
+    it "returns an error with the code set to -32700 there is a JSON parse error" do
+      # Defer to handle_json for JSON parsing
+      handle_json "Invalid JSON"
+
+      assert_rpc_error expected_error: {
+        code: -32700,
+        message: "Parse error",
+        data: "Invalid JSON",
+      }
+    end
+
+    it "returns an error with code set to -32600 when the request is not an array or a hash" do
+      handle true
+
+      assert_rpc_error expected_error: {
+        code: -32600,
+        message: "Invalid Request",
+        data: "Request must be an array or a hash",
+      }
+    end
+
+    it "returns an error with the code set to -32601 when the method does not exist" do
+      handle jsonrpc: "2.0", id: 1, method: "add", params: { a: 1, b: 2 }
+
+      assert_rpc_error expected_error: {
+        code: -32601,
+        message: "Method not found",
+        data: "add",
+      }
+    end
+
+    it "returns nil when the method does not exist and the id is nil" do
+      handle jsonrpc: "2.0", method: "add", params: { a: 1, b: 2 }
+
+      assert_nil @response
+    end
+
+    it "returns an error with the code set to -32602 when the method parameters are invalid" do
+      handle jsonrpc: "2.0", id: 1, method: "set_active", params: true
+
+      assert_rpc_error expected_error: {
+        code: -32602,
+        message: "Invalid params",
+        data: "Method parameters must be an array or an object or null",
+      }
+    end
+
+    it "returns an error with the code set to -32603 when there is an internal error" do
+      register("add") { raise StandardError, "Something bad happened" }
+
+      handle jsonrpc: "2.0", id: 1, method: "add"
+
+      assert_rpc_error expected_error: {
+        code: -32603,
+        message: "Internal error",
+        data: "Something bad happened",
+      }
+    end
+
+    # 6 Batch
+    #
+    # To send several Request objects at the same time, the Client MAY send an Array filled with Request objects.
+    #
+    # The Server should respond with an Array containing the corresponding Response objects, after all of the batch
+    # Request objects have been processed. A Response object SHOULD exist for each Request object, except that there
+    # SHOULD NOT be any Response objects for notifications. The Server MAY process a batch rpc call as a set of
+    # concurrent tasks, processing them in any order and with any width of parallelism.
+    #
+    # The Response objects being returned from a batch call MAY be returned in any order within the Array. The Client
+    # SHOULD match contexts between the set of Request objects and the resulting set of Response objects based on the id
+    # member within each Object.
+    #
+    # If the batch rpc call itself fails to be recognized as an valid JSON or as an Array with at least one value, the
+    # response from the Server MUST be a single Response object. If there are no Response objects contained within the
+    # Response array as it is to be sent to the client, the server MUST NOT return an empty Array and should return
+    # nothing at all.
+
+    describe "with batch request" do
+      it "returns an invalid request error when the request is an empty array" do
+        handle []
+
+        assert_rpc_error expected_error: {
+          code: -32600,
+          message: "Invalid Request",
+          data: "Request is an empty array",
+        }
+      end
+
+      it "returns an array of Response objects" do
+        register("add") { |params| params[:a] + params[:b] }
+        register("mul") { |params| params[:a] * params[:b] }
+
+        handle [
+          { jsonrpc: "2.0", id: 100, method: "add", params: { a: 1, b: 2 } },
+          { jsonrpc: "2.0", id: 200, method: "mul", params: { a: 3, b: 4 } },
+        ]
+
+        assert @response.is_a?(Array)
+        assert @response.all? { |result| result[:jsonrpc] == "2.0" }
+        assert_equal [100, 200], @response.map { |result| result[:id] }
+        assert_equal [3, 12], @response.map { |result| result[:result] }
+        assert @response.all? { |result| result[:error].nil? }
+      end
+
+      it "returns an array of Response objects excluding notifications" do
+        register("ping") {}
+        register("add") { |params| params[:a] + params[:b] }
+
+        handle [
+          { jsonrpc: "2.0", method: "ping" },
+          { jsonrpc: "2.0", id: 100, method: "add", params: { a: 1, b: 2 } },
+          { jsonrpc: "2.0", id: 200, method: "add", params: { a: 2, b: 3 } },
+        ]
+
+        assert @response.is_a?(Array)
+        assert @response.all? { |result| result[:jsonrpc] == "2.0" }
+        assert_equal [100, 200], @response.map { |result| result[:id] }
+        assert_equal [3, 5], @response.map { |result| result[:result] }
+        assert @response.all? { |result| result[:error].nil? }
+      end
+
+      it "returns a single response object when the batch has only a single response" do
+        register("ping") {}
+        register("add") { |params| params[:a] + params[:b] }
+
+        handle [
+          { jsonrpc: "2.0", method: "ping" },
+          { jsonrpc: "2.0", id: 100, method: "add", params: { a: 1, b: 2 } },
+        ]
+
+        assert_rpc_success expected_result: 3
+      end
+
+      it "returns nil when the batch has only notifications" do
+        register("ping") {}
+        register("pong") {}
+
+        handle [
+          { jsonrpc: "2.0", method: "ping" },
+          { jsonrpc: "2.0", method: "pong" },
+        ]
+
+        assert_nil @response
+      end
+    end
+
+    # 7 Examples
+    # ...
+    # 8 Extensions
+    #
+    # Method names that begin with rpc. are reserved for system extensions, and MUST NOT be used for anything else. Each
+    # system extension is defined in a related specification. All system extensions are OPTIONAL.
+
+    describe "ID pattern configuration" do
+      it "uses the default pattern by default" do
+        register("add") { |params| params[:a] + params[:b] }
+
+        handle jsonrpc: "2.0", id: "valid-id_123", method: "add", params: { a: 1, b: 2 }
+
+        assert_rpc_success expected_result: 3
+      end
+
+      it "rejects IDs that don't match the default pattern" do
+        handle jsonrpc: "2.0", id: "invalid@id", method: "add", params: { a: 1, b: 2 }
+
+        assert_rpc_error expected_error: {
+          code: -32600,
+          message: "Invalid Request",
+          data: "Request ID must match validation pattern, or be an integer or null",
+        }
+      end
+
+      it "uses default pattern and rejects @ signs" do
+        register("add") { |params| params[:a] + params[:b] }
+
+        # Default pattern should reject @ signs
+        handle jsonrpc: "2.0", id: "user@example.com", method: "add", params: { a: 1, b: 2 }
+
+        assert_rpc_error expected_error: {
+          code: -32600,
+          message: "Invalid Request",
+          data: "Request ID must match validation pattern, or be an integer or null",
+        }
+      end
+
+      it "accepts custom pattern as parameter to handle" do
+        register("add") { |params| params[:a] + params[:b] }
+        custom_pattern = /\A[a-zA-Z0-9_.\-@]+\z/
+
+        @response = JsonRpcHandler.handle(
+          { jsonrpc: "2.0", id: "user@example.com", method: "add", params: { a: 1, b: 2 } },
+          id_validation_pattern: custom_pattern,
+        ) { |method_name| @registry[method_name] }
+
+        assert_rpc_success expected_result: 3
+        assert_equal "user@example.com", @response[:id]
+      end
+
+      it "validates against custom pattern parameter" do
+        custom_pattern = /\A[a-zA-Z0-9_.\-@]+\z/
+
+        @response = JsonRpcHandler.handle(
+          { jsonrpc: "2.0", id: "id<script>", method: "add", params: { a: 1, b: 2 } },
+          id_validation_pattern: custom_pattern,
+        ) { |method_name| @registry[method_name] }
+
+        assert_rpc_error expected_error: {
+          code: -32600,
+          message: "Invalid Request",
+          data: "Request ID must match validation pattern, or be an integer or null",
+        }
+      end
+
+      it "accepts custom pattern as parameter to handle_json" do
+        register("add") { |params| params[:a] + params[:b] }
+        custom_pattern = /\A[a-zA-Z0-9_.\-@]+\z/
+
+        @response_json = JsonRpcHandler.handle_json(
+          { jsonrpc: "2.0", id: "user@example.com", method: "add", params: { a: 1, b: 2 } }.to_json,
+          id_validation_pattern: custom_pattern,
+        ) { |method_name| @registry[method_name] }
+        @response = JSON.parse(@response_json, symbolize_names: true)
+
+        assert_rpc_success expected_result: 3
+        assert_equal "user@example.com", @response[:id]
+      end
+
+      it "applies custom pattern to batch requests" do
+        register("add") { |params| params[:a] + params[:b] }
+        register("mul") { |params| params[:a] * params[:b] }
+        custom_pattern = /\A[a-zA-Z0-9_.\-@]+\z/
+
+        @response = JsonRpcHandler.handle(
+          [
+            { jsonrpc: "2.0", id: "req@1", method: "add", params: { a: 1, b: 2 } },
+            { jsonrpc: "2.0", id: "req@2", method: "mul", params: { a: 3, b: 4 } },
+          ],
+          id_validation_pattern: custom_pattern,
+        ) { |method_name| @registry[method_name] }
+
+        assert @response.is_a?(Array)
+        assert_equal ["req@1", "req@2"], @response.map { |r| r[:id] }
+        assert_equal [3, 12], @response.map { |r| r[:result] }
+      end
+
+      it "parameter pattern overrides default pattern" do
+        register("add") { |params| params[:a] + params[:b] }
+        # Use permissive parameter pattern (default is restrictive)
+        custom_pattern = /\A[a-zA-Z0-9_.\-@]+\z/
+
+        @response = JsonRpcHandler.handle(
+          { jsonrpc: "2.0", id: "user@example.com", method: "add", params: { a: 1, b: 2 } },
+          id_validation_pattern: custom_pattern,
+        ) { |method_name| @registry[method_name] }
+
+        assert_rpc_success expected_result: 3
+        assert_equal "user@example.com", @response[:id]
+      end
+
+      it "accepts any string when pattern is nil" do
+        register("add") { |params| params[:a] + params[:b] }
+
+        @response = JsonRpcHandler.handle(
+          { jsonrpc: "2.0", id: "<script>alert('xss')</script>", method: "add", params: { a: 1, b: 2 } },
+          id_validation_pattern: nil,
+        ) { |method_name| @registry[method_name] }
+
+        assert_rpc_success expected_result: 3
+        assert_equal "<script>alert('xss')</script>", @response[:id]
+      end
+    end
+  end
+
+  describe "#handle_json" do
+    it "returns a Response object when the request is valid and not a notification" do
+      register("add") { |params| params[:a] + params[:b] }
+
+      handle_json({ jsonrpc: "2.0", id: 1, method: "add", params: { a: 1, b: 2 } }.to_json)
+
+      assert_rpc_success(expected_result: 3)
+    end
+
+    it "returns nil for notifications" do
+      register("ping") {}
+
+      handle_json({ jsonrpc: "2.0", method: "ping" }.to_json)
+
+      assert_nil @response
+    end
+
+    it "returns an error with the id set to nil when the request is invalid" do
+      handle_json({ jsonrpc: "0.0", id: 1, method: "add", params: { a: 1, b: 2 } }.to_json)
+
+      assert_nil @response[:id]
+    end
+  end
+
+  private
+
+  def register(method_name, &block)
+    @registry[method_name] = block
+  end
+
+  def handle(request)
+    @response = JsonRpcHandler.handle(request) { |method_name| @registry[method_name] }
+  end
+
+  def handle_json(request_json)
+    @response_json = JsonRpcHandler.handle_json(request_json) { |method_name| @registry[method_name] }
+    @response = JSON.parse(@response_json, symbolize_names: true) if @response_json
+  end
+
+  def assert_rpc_success(expected_result:)
+    assert_equal(expected_result, @response[:result])
+    assert_nil(@response[:error])
+  end
+
+  def assert_rpc_error(expected_error:)
+    assert_equal(expected_error, @response[:error])
+    assert_nil(@response[:result])
+  end
+end