Add prompts/list and prompts/get support to client

This commit adds two new methods to `MCP::Client`:
- prompts: Lists available prompts from the server via `prompts/list`
- get_prompt: Retrieves a specific prompt by name via `prompts/get`

Both methods follow the same pattern as the existing resources support,
including comprehensive test coverage and README documentation updates.

ref. https://github.com/modelcontextprotocol/modelcontextprotocol/blob/main/docs/specification/2025-03-26/server/prompts.mdx#protocol-messages

Author: dak2

README.md

@@ -830,6 +830,8 @@ This class supports:
 - Tool invocation via the `tools/call` method (`MCP::Client#call_tools`)
 - Resource listing via the `resources/list` method (`MCP::Client#resources`)
 - Resource reading via the `resources/read` method (`MCP::Client#read_resources`)
+- Prompt listing via the `prompts/list` method (`MCP::Client#prompts`)
+- Prompt retrieval via the `prompts/get` method (`MCP::Client#get_prompt`)
 - Automatic JSON-RPC 2.0 message formatting
 - UUID request ID generation
 

lib/mcp/client.rb

@@ -58,6 +58,20 @@ def resources
       response.dig("result", "resources") || []
     end
 
+    # Returns the list of prompts available from the server.
+    # Each call will make a new request – the result is not cached.
+    #
+    # @return [Array<Hash>] An array of available prompts.
+    def prompts
+      response = transport.send_request(request: {
+        jsonrpc: JsonRpcHandler::Version::V2_0,
+        id: request_id,
+        method: "prompts/list",
+      })
+
+      response.dig("result", "prompts") || []
+    end
+
     # Calls a tool via the transport layer and returns the full response from the server.
     #
     # @param tool [MCP::Client::Tool] The tool to be called.
@@ -96,6 +110,21 @@ def read_resource(uri:)
       response.dig("result", "contents") || []
     end
 
+    # Gets a prompt from the server by name and returns its details.
+    #
+    # @param name [String] The name of the prompt to get.
+    # @return [Hash] A hash containing the prompt details.
+    def get_prompt(name:)
+      response = transport.send_request(request: {
+        jsonrpc: JsonRpcHandler::Version::V2_0,
+        id: request_id,
+        method: "prompts/get",
+        params: { name: name },
+      })
+
+      response.fetch("result", {})
+    end
+
     private
 
     def request_id

test/mcp/client_test.rb

@@ -141,5 +141,135 @@ def test_read_resource_returns_empty_array_when_no_contents
 
       assert_empty(contents)
     end
+
+    def test_prompts_sends_request_to_transport_and_returns_prompts_array
+      transport = mock
+      mock_response = {
+        "result" => {
+          "prompts" => [
+            {
+              "name" => "prompt_1",
+              "description" => "First prompt",
+              "arguments" => [
+                {
+                  "name" => "code_1",
+                  "description" => "The code_1 to review",
+                  "required" => true,
+                },
+              ],
+            },
+            {
+              "name" => "prompt_2",
+              "description" => "Second prompt",
+              "arguments" => [
+                {
+                  "name" => "code_2",
+                  "description" => "The code_2 to review",
+                  "required" => true,
+                },
+              ],
+            },
+          ],
+        },
+      }
+
+      # Only checking for the essential parts of the request
+      transport.expects(:send_request).with do |args|
+        args in { request: { method: "prompts/list", jsonrpc: "2.0" } }
+      end.returns(mock_response).once
+
+      client = Client.new(transport: transport)
+      prompts = client.prompts
+
+      assert_equal(2, prompts.size)
+      assert_equal("prompt_1", prompts.first["name"])
+      assert_equal("First prompt", prompts.first["description"])
+      assert_equal("code_1", prompts.first["arguments"].first["name"])
+      assert_equal("The code_1 to review", prompts.first["arguments"].first["description"])
+      assert(prompts.first["arguments"].first["required"])
+
+      assert_equal("prompt_2", prompts.last["name"])
+      assert_equal("Second prompt", prompts.last["description"])
+      assert_equal("code_2", prompts.last["arguments"].first["name"])
+      assert_equal("The code_2 to review", prompts.last["arguments"].first["description"])
+      assert(prompts.last["arguments"].first["required"])
+    end
+
+    def test_prompts_returns_empty_array_when_no_prompts
+      transport = mock
+      mock_response = { "result" => { "prompts" => [] } }
+
+      transport.expects(:send_request).returns(mock_response).once
+
+      client = Client.new(transport: transport)
+      prompts = client.prompts
+
+      assert_empty(prompts)
+    end
+
+    def test_get_prompt_sends_request_to_transport_and_returns_contents
+      transport = mock
+      name = "first_prompt"
+      mock_response = {
+        "result" => {
+          "description" => "First prompt",
+          "messages" => [
+            {
+              "role" => "user",
+              "content" => {
+                "text" => "First prompt content",
+                "type" => "text",
+              },
+            },
+          ],
+        },
+      }
+
+      # Only checking for the essential parts of the request
+      transport.expects(:send_request).with do |args|
+        args in {
+          request: {
+            method: "prompts/get",
+            jsonrpc: "2.0",
+            params: {
+              name: name,
+            },
+          },
+        }
+      end.returns(mock_response).once
+
+      client = Client.new(transport: transport)
+      contents = client.get_prompt(name: name)
+
+      assert_equal("First prompt", contents["description"])
+      assert_equal("user", contents["messages"].first["role"])
+      assert_equal("First prompt content", contents["messages"].first["content"]["text"])
+    end
+
+    def test_get_prompt_returns_empty_hash_when_no_contents
+      transport = mock
+      name = "nonexistent_prompt"
+      mock_response = { "result" => {} }
+
+      transport.expects(:send_request).returns(mock_response).once
+
+      client = Client.new(transport: transport)
+      contents = client.get_prompt(name: name)
+
+      assert_empty(contents)
+    end
+
+    def test_get_prompt_returns_empty_hash
+      transport = mock
+      name = "nonexistent_prompt"
+      mock_response = {}
+
+      transport.expects(:send_request).returns(mock_response).once
+
+      client = Client.new(transport: transport)
+      contents = client.get_prompt(name: name)
+
+      assert_empty(contents)
+    end
   end
 end