feat: server prompts #21

cs3b · 2025-04-01T01:34:34Z

Updated: Prompts Feature with Main Branch Alignment

This PR has been rebased onto main and updated to align with current architecture.

Major Changes from Rebase:

1. ServerFiltering Integration

Prompts now support the filtering architecture
Dynamic prompt filtering based on request context
Consistent with tool and resource filtering

2. Feature Parity with Tools

Added tags support to prompts
Added metadata support
Added annotations support
Added authorization blocks
Headers parameter for all prompts

3. Rails Integration

Generator creates app/prompts/ directory
ApplicationPrompt base class
Auto-discovery of prompt descendants
ActionPrompt alias for Rails conventions

Testing:

All tests updated for new architecture
New tests for prompt features
Integration tests passing
MCP inspector validated

Addresses Reviewer Feedback:

✅ ApplicationPrompt.descendants registration implemented
✅ Rails generator updated with demo prompt generation
✅ Consistent with tools/resources patterns
✅ All architectural changes from main branch integrated

cs3b · 2025-04-01T01:38:39Z

@yjacquin it's still a WIP, please look at the examples - do you like dsl like this (we have to handle multiple message on the output), and i see value to have support for erb templates for prompts (might be especial useful if you want to keep the in certain format markdown md.erb / xml - xml.erb )

Just let me know how do you see it

yjacquin · 2025-04-02T19:50:01Z

@yjacquin it's still a WIP, please look at the examples - do you like dsl like this (we have to handle multiple message on the output), and i see value to have support for erb templates for prompts (might be especial useful if you want to keep the in certain format markdown md.erb / xml - xml.erb )

Just let me know how do you see it

@cs3b I love it ! The erb template is a clever addition.
Thanks a lot for your qualitative work :)
Let me know if I can help you with this PR !
Sorry I haven't been able to review earlier 🙏

cs3b · 2025-04-03T23:45:17Z

Feature ready to review and merge @yjacquin

yjacquin

Thanks a lot @cs3b for the great work !
I think it's a great feature to add and we're near it being ready to get merged and added to the incoming 1.1.0.

We could also add this to the rails integration in the same fashion it has been done for tools and resources, wdyt ? It can also be done in a later iteration.

lib/mcp/prompt.rb

Gemfile.lock

lib/mcp/version.rb

lib/mcp/server.rb

lib/mcp/prompt.rb

examples/prompts/inline_prompt.rb

lib/mcp/server.rb

lib/mcp/prompt.rb

- Removed multi_message_prompt.rb as it's no longer needed after simplifying the messages API - The example was demonstrating the array-based API which has been removed in Task 3 - The inline_prompt.rb example now serves as the primary example for prompt functionality This change aligns the examples with the implementation changes made in PR yjacquin#21.

Key changes: - Added robust prompt registration and handling in Server class - Implemented base64 validation for image content to ensure MCP compliance - Simplified messages API to use only keyword arguments for better usability - Refactored code to follow DRY principles and improve maintainability - Updated tool_name method to follow the same pattern as prompt_name - Fixed unused parameters and linter warnings throughout the codebase - Added comprehensive test coverage for all new functionality - Added example prompts to demo files for easy adoption - Reverted version to 1.0.0 as requested by maintainer This implementation enables developers to create and register prompts that can generate messages with text, image, and resource content, following the MCP specification. The code is thoroughly tested and includes examples to demonstrate proper usage. All tasks from PR yjacquin#21 feedback have been addressed

cs3b · 2025-04-14T00:27:44Z

I've applied feedback and rebased against main. Keep the commits unsquashed so it will easier to review

hope this time we will be able to merge :-)

Waiting for your feedback @yjacquin

mariochavez · 2025-05-26T16:35:25Z

Hi! I wasn't aware of this Pull Request, so yesterday I added support for prompts too. https://github.com/mariochavez/fast-mcp/tree/add-prompt-support

If this PR is ready, other than the current merge conflicts, can we expect it to land anytime soon?

nfedyashev · 2025-06-03T15:16:42Z

examples/prompts/prompt_code_review.rb

+
+      def call(code:, programming_language: nil)
+        assistant_template = File.read(File.join(File.dirname(__FILE__), 'templates/code_review_assistant.erb'))
+        user_template = File.read(File.join(File.dirname(__FILE__), 'templates/code_review_user.erb'))


these files are not that big, perhaps it would be easy to read and use as inline ERB templates right in this file.

I'm not part of the team, so this is for @yjacquin to decide

yes, in case of prompt is short inline is recommended - this is just an example, that it is possible

nfedyashev · 2025-06-03T15:20:19Z

README.md


+# Define a prompt by inheriting from FastMcp::Prompt
+class GreetingPrompt < FastMcp::Prompt
+  prompt_name 'greeting'


perhaps this can be just "name"? prompt_name within FastMcp::Prompt sounds a bit repetitive.

Python https://gofastmcp.com/servers/prompts
and
node https://github.com/punkpeye/fastmcp/blob/main/src/examples/addition.ts#L170 version call it just "name".

/cc @yjacquin

In Ruby, using :name as an attribute can be problematic in certain contexts due to naming conflicts.

Module.name # => "Module" MyClass.name # => "MyClass" some_object.name # can be defined implicitly

Additionaly this the convention for this project see

fast-mcp/lib/mcp/tool.rb

Line 126 in 3d5a7e5

def tool_name(name = nil)

there was no feedback from the @yjacquin since beginning of April ( until he will say what next, i'm not working actively on this). Still prompts are a very powerful feature (especial when mcp is attached to ai agent)

Linell · 2025-06-13T01:15:05Z

Thank you for your work on this! I would love to see it merged into main soon.

nfedyashev · 2025-06-15T19:05:41Z

docs/prompts.md

+
+  arguments do
+    required(:document_type).filled(:string).description("Type of XML document")
+    required(:elements).array.description("Elements to include")


@cs3b I think there must be a typo here

/home/nfedyashev/.rbenv/versions/3.1.3/lib/ruby/gems/3.1.0/gems/dry-schema-1.14.1/lib/dry/schema/macros/value.rb:62:in `call': wrong number of arguments (given 0, expected at least 1) (ArgumentError) from /home/nfedyashev/.rbenv/versions/3.1.3/lib/ruby/gems/3.1.0/gems/dry-schema-1.14.1/lib/dry/schema/macros/dsl.rb:63:in `block (2 levels) in value' from /home/nfedyashev/.rbenv/versions/3.1.3/lib/ruby/gems/3.1.0/gems/dry-schema-1.14.1/lib/dry/schema/macros/dsl.rb:208:in `append_macro' from /home/nfedyashev/.rbenv/versions/3.1.3/lib/ruby/gems/3.1.0/gems/dry-schema-1.14.1/lib/dry/schema/macros/dsl.rb:62:in `block in value' from /home/nfedyashev/.rbenv/versions/3.1.3/lib/ruby/gems/3.1.0/gems/dry-schema-1.14.1/lib/dry/schema/macros/dsl.rb:251:in `extract_type_spec' from /home/nfedyashev/.rbenv/versions/3.1.3/lib/ruby/gems/3.1.0/gems/dry-schema-1.14.1/lib/dry/schema/macros/dsl.rb:61:in `value' from /home/nfedyashev/.rbenv/versions/3.1.3/lib/ruby/gems/3.1.0/gems/dry-schema-1.14.1/lib/dry/schema/macros/array.rb:22:in `block in value' from /home/nfedyashev/.rbenv/versions/3.1.3/lib/ruby/gems/3.1.0/gems/dry-schema-1.14.1/lib/dry/schema/macros/dsl.rb:251:in `extract_type_spec' from /home/nfedyashev/.rbenv/versions/3.1.3/lib/ruby/gems/3.1.0/gems/dry-schema-1.14.1/lib/dry/schema/macros/array.rb:16:in `value' from /home/nfedyashev/.rbenv/versions/3.1.3/lib/ruby/gems/3.1.0/gems/dry-schema-1.14.1/lib/dry/schema/macros/dsl.rb:178:in `block in array' from /home/nfedyashev/.rbenv/versions/3.1.3/lib/ruby/gems/3.1.0/gems/dry-schema-1.14.1/lib/dry/schema/macros/dsl.rb:208:in `append_macro' from /home/nfedyashev/.rbenv/versions/3.1.3/lib/ruby/gems/3.1.0/gems/dry-schema-1.14.1/lib/dry/schema/macros/dsl.rb:177:in `array' from /home/nfedyashev/Projects/appfoo/app/resources/xml_prompt.rb:7:in `block in <class:XmlPrompt>'

.array(:hash). doesn't seem to work either:

Invalid arguments for prompt xml_generator: {"elements":["must be an array"],"attributes":["must be a hash"]} Sending response: {:jsonrpc=>"2.0", :error=>{:code=>-32602, :message=>"{\"elements\":[\"must be an array\"],\"attributes\":[\"must be a hash\"]}"}, :id=>8}

nfedyashev · 2025-06-15T19:15:03Z

@cs3b A few comments

perhaps this PR can be slightly updated to be more consistent with how tools and resources are configured.
From what I see it is lacking a way to register all prompts(*ApplicationPrompt.descendants)

https://github.com/yjacquin/fast-mcp?tab=readme-ov-file#-fast-ruby-on-rails-implementation

install_generator is a bit outdated and seems like lacking demo prompt generation
https://github.com/yjacquin/fast-mcp/blob/main/lib/generators/fast_mcp/install/install_generator.rb#L28 in this case README needs to be updated as well

nfedyashev · 2025-06-15T19:15:45Z

Other than a few comments above it works great! Thank you very much @cs3b

grantmca · 2025-08-13T14:26:47Z

Hey! This MR looks great, wanted to check in on the status, looks like it has been on hold for a couple of months. @yjacquin What does the timeline look like for supporting prompts? Thanks for all the great work @cs3b!

pyrabbit · 2025-08-13T23:25:41Z

Would love to see this merged -- let me know if I can help.

cs3b · 2025-08-17T22:21:59Z

Feature ready to review and merge @yjacquin

/cc @pyrabbit @grantmca @nfedyashev @Linell @mariochavez

Implements full Model Context Protocol (MCP) prompts support per specification. Core Features: - New Prompt class with message creation and validation - Dry::Schema-based argument validation (same as tools) - ERB template support for structured prompt messages - Multiple message formats (hash, array, MessageBuilder pattern) - Support for text, image, and resource content types API Design: - MessageBuilder for fluent message construction - Flexible messages() method supporting multiple same-role messages - Base64 validation for image content compliance - Auto-naming from class names (CodeReviewPrompt → code_review) Feature Parity with Tools: - Authorization blocks for access control - Tags, metadata, and annotations support - Integration with ServerFiltering for dynamic filtering - Headers support for authorization context Server Integration: - Added prompts/list and prompts/get endpoints - Prompt registration methods (register_prompt, register_prompts) - Notification support for prompts list changes Rails Support: - Generator for creating new prompts (rails g fast_mcp:install) - ApplicationPrompt base class - Auto-loading from app/prompts directory - Sample prompt template with best practices Testing & Documentation: - 900+ lines of comprehensive tests - Example prompts (few-shot, inline, code review with templates) - Full documentation in docs/prompts.md - Rails integration guide updates Breaking Changes: None - purely additive feature

nfedyashev · 2025-08-21T15:56:02Z

@cs3b I haven't reviewed the latest code updates, but as a user I can confirm that it works fine. I'm currently using it as fork of fast-mcp before it gets merged.
Thanks a lot for your effort. Much appreciated

cs3b marked this pull request as draft April 1, 2025 01:38

cs3b force-pushed the server-prompts-feature branch 3 times, most recently from b75c14c to 191a3a0 Compare April 3, 2025 21:29

cs3b marked this pull request as ready for review April 3, 2025 23:36

cs3b changed the title ~~(WIP) Server prompts feature~~ Feature :: Server :: Prompts Apr 3, 2025

cs3b changed the title ~~Feature :: Server :: Prompts~~ feat: server prompts Apr 3, 2025

yjacquin reviewed Apr 10, 2025

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cs3b force-pushed the server-prompts-feature branch from 9941bcf to 4ebfbf6 Compare April 14, 2025 00:14

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cs3b force-pushed the server-prompts-feature branch from 46d5948 to f1835b3 Compare April 14, 2025 00:21

nfedyashev reviewed Jun 3, 2025

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nfedyashev reviewed Jun 15, 2025

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nfedyashev mentioned this pull request Jun 19, 2025

Support MCP Prompts #101

Open

cs3b force-pushed the server-prompts-feature branch from 5e25cca to 26b9871 Compare August 17, 2025 21:53

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cs3b requested review from nfedyashev and yjacquin August 18, 2025 10:12

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feat: server prompts #21

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cs3b commented Apr 1, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Updated: Prompts Feature with Main Branch Alignment

Major Changes from Rebase:

1. ServerFiltering Integration

2. Feature Parity with Tools

3. Rails Integration

Testing:

Addresses Reviewer Feedback:

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cs3b commented Apr 1, 2025

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