experimental-ext-variants/README.md

MCP Variants (Experimental Extension)

Status: Experimental. This work is for prototyping and feedback only, and is not an accepted or official MCP extension.

This repository provides a multi-language reference implementation of the variants proposal for the Model Context Protocol (MCP), as described in SEP-2053.

Implementations

Language	Directory	Package	Status
Go	go/sdk/	github.com/modelcontextprotocol/experimental-ext-variants/go/sdk	Planned
Python	python/sdk/	mcp-ext-variants	Planned
TypeScript	typescript/sdk/	@ext-modelcontextprotocol/variants	Planned

Examples (Go)

The Go implementation includes runnable example servers under go/sdk/examples/server/:

model-optimized/

Same tools, different descriptions per LLM family.

https://github.com/user-attachments/assets/5bb60cd2-291f-4940-abfe-f53852d35470

github/

Different tool sets per variant with custom ranking.

https://github.com/user-attachments/assets/d770ac55-e988-4d89-bdf8-bcb3cf1e2e53

research/

Context budget management via description verbosity.

trading/

API versioning, lifecycle statuses, and deprecation info.

variants-stdio/

Minimal single-variant setup.

CI/CD

This monorepo uses path-based CI workflows to efficiently test only what changes:

How It Works

1. Language-specific workflows (python.yml, go.yml, typescript.yml)

   • Only trigger when their language directory or workflow file changes
   • Run all tests, linting, and checks for that language

2. Status check workflow (status-check.yml)

   • Runs on every PR to verify required checks passed
   • Determines what needs to pass based on which files changed
   • This is the only required check in branch protection

Examples

• Change python/sdk/file.py → Only Python CI runs → PR requires Python checks to pass
• Change both Go and TypeScript files → Both CIs run → PR requires both to pass
• Change only README.md → No language CIs run → PR can merge immediately

Forcing All Checks

To run all language checks regardless of changed files:

• In a PR: Comment /test all (only works for repo owners/members/collaborators)
• Manually: Use GitHub Actions UI or CLI to trigger individual workflows

Adding New Required Checks

1. Add your check to the appropriate language workflow (e.g., python.yml):

   python-security-scan:
     name: "Security Scan"
     runs-on: ubuntu-latest
     steps:
       - name: Run security checks
         run: # your commands here
   

2. Update the status check in .github/workflows/status-check.yml:

   const requiredChecks = {
     python: [
       'Python CI / Linting',
       'Python CI / Unit Tests (3.10)',
       // ... existing checks ...
       'Python CI / Security Scan'  // ← Add your new check
     ],
   

3. Submit PR - Your new check is now required for all relevant changes!

License

Apache License 2.0 - See LICENSE file for details

Resources

• Variants Proposal Specification (SEP-2053) - Full specification and design details
• Model Context Protocol