feat: Add comprehensive MCP prompts implementation

This PR adds full support for MCP prompts following the specification:

Core Features:
- Complete prompts API with message creation and validation
- Dry::Schema-based argument validation like tools
- ERB template support for structured messages
- Multiple message format support (hash, array, builder pattern)
- Support for text, image, and resource content types

Architecture Enhancements:
- Feature parity with tools (tags, metadata, annotations, authorization)
- Prompt filtering support integrated with ServerFiltering
- Stateless architecture matching resources pattern
- Auto-naming from class names (CodeReviewPrompt → code_review)
- Headers support for authorization context

API Improvements:
- Flexible messages API supporting multiple same-role messages
- MessageBuilder for fluent message construction
- Base64 validation for image content
- Comprehensive content type handling

Rails Integration:
- Rails generator support for prompts
- ApplicationPrompt base class
- Auto-discovery of prompt descendants
- Sample prompt template included

Testing & Documentation:
- Extensive test coverage (900+ lines)
- Complete documentation with examples
- Rails integration guide updates
- Template validation tests

Breaking Changes:
- Resources now stateless (documented in CHANGELOG)

Co-authored-by: @nfedyashev (review feedback)

Author: cs3b

.gitignore

@@ -1,4 +1,3 @@
-
 # Ignore RSpec status file
 /.rspec_status
 

CHANGELOG.md

@@ -8,6 +8,17 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## [Unreleased]
 ### Added
 - Tool annotations support for providing hints about tool behavior (readOnlyHint, destructiveHint, etc.)
+- Comprehensive Prompts Feature implementation following MCP specification
+  - Full MCP prompts protocol support
+  - Prompt templates with ERB support
+  - Prompt argument validation using Dry::Schema
+  - Prompt filtering support with ServerFiltering architecture
+  - MessageBuilder for fluent message construction API
+  - Auto-naming from class names (e.g., `CodeReviewPrompt` → `code_review`)
+  - Support for authorization, tags, metadata, and prompt annotations
+  - Base64 validation for image content to ensure MCP compliance
+  - Flexible API for the `messages` method supporting hash, array, and block formats
+  - Rails generator templates for creating prompts
 
 ## [1.5.0] - 2025-06-01
 ### Added

Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    fast-mcp (1.5.0)
+    fast-mcp (1.6.0)
       addressable (~> 2.8)
       base64
       dry-schema (~> 1.14)

README.md

@@ -28,13 +28,13 @@ Fast MCP solves all these problems by providing a clean, Ruby-focused implementa
 
 - 🛠️ **Tools API** - Let AI models call your Ruby functions securely, with in-depth argument validation through [Dry-Schema](https://github.com/dry-rb/dry-schema).
 - 📚 **Resources API** - Share data between your app and AI models
+- 💬 **Prompt Handling** - Create structured message templates for LLM interactions
 - 🔄 **Multiple Transports** - Choose from STDIO, HTTP, or SSE based on your needs
 - 🧩 **Framework Integration** - Works seamlessly with Rails, Sinatra or any Rack app.
 - 🔒 **Authentication Support** - Secure your AI-powered endpoints with ease
 - 🚀 **Real-time Updates** - Subscribe to changes for interactive applications
 - 🎯 **Dynamic Filtering** - Control tool/resource access based on request context (permissions, API versions, etc.)
 
-
 ## 💎 What Makes FastMCP Great
 ```ruby
 # Define tools for AI models to use
@@ -269,6 +269,27 @@ end
 # Register the resource with the server
 server.register_resource(StatisticsResource)
 
+# Define prompts for structured AI interactions
+class CodeReviewPrompt < FastMcp::Prompt
+  # prompt_name is automatically generated as "code_review" from class name
+  description "Review code for best practices"
+  
+  arguments do
+    required(:code).filled(:string)
+    required(:language).filled(:string)
+  end
+  
+  def call(code:, language:)
+    messages(
+      assistant: "I'll review your #{language} code for best practices and potential improvements.",
+      user: "Please review this #{language} code:\n\n```#{language}\n#{code}\n```\n\nFocus on readability, performance, and maintainability."
+    )
+  end
+end
+
+# Register the prompt with the server
+server.register_prompt(CodeReviewPrompt)
+
 # Start the server
 server.start
 ```
@@ -338,6 +359,7 @@ Add your server to your Claude Desktop configuration at:
 ```
 
 ## How to add a MCP server to Claude, Cursor, or other MCP clients?
+
 Please refer to [configuring_mcp_clients](docs/configuring_mcp_clients.md)
 
 ## 📊 Supported Specifications
@@ -347,6 +369,7 @@ Please refer to [configuring_mcp_clients](docs/configuring_mcp_clients.md)
 | ✅ **JSON-RPC 2.0** | Full implementation for communication |
 | ✅ **Tool Definition & Calling** | Define and call tools with rich argument types |
 | ✅ **Resource & Resource Templates Management** | Create, read, update, and subscribe to resources |
+| ✅ **Prompt Handling** | Create structured message templates for LLM interactions |
 | ✅ **Transport Options** | STDIO, HTTP, and SSE for flexible integration |
 | ✅ **Framework Integration** | Rails, Sinatra, Hanami, and any Rack-compatible framework |
 | ✅ **Authentication** | Secure your AI endpoints with token authentication |
@@ -398,6 +421,7 @@ FastMcp.authenticated_rack_middleware(app,
 - [🌐 Sinatra Integration](docs/sinatra_integration.md)
 - [📚 Resources](docs/resources.md)
 - [🛠️ Tools](docs/tools.md)
+- [💬 Prompts](docs/prompts.md)
 - [🔒 Security](docs/security.md)
 - [🎯 Dynamic Filtering](docs/filtering.md)
 
@@ -408,6 +432,7 @@ Check out the [examples directory](examples) for more detailed examples:
 - **🔨 Basic Examples**:
   - [Simple Server](examples/server_with_stdio_transport.rb)
   - [Tool Examples](examples/tool_examples.rb)
+  - [Prompt Examples](examples/prompts)
 
 - **🌐 Web Integration**:
   - [Rack Middleware](examples/rack_middleware.rb)
@@ -437,4 +462,4 @@ This project is available as open source under the terms of the [MIT License](ht
 
 - The [Model Context Protocol](https://github.com/modelcontextprotocol) team for creating the specification
 - The [Dry-Schema](https://github.com/dry-rb/dry-schema) team for the argument validation.
-- All contributors to this project
+- All contributors to this project