Experimental Interceptors
Status: Experimental. This repository provides a multi-language reference implementation of the proposed interceptor extension for the Model Context Protocol (MCP), as described in SEP-1763.
What is Experimental Interceptors?
Experimental Interceptors is a Model Context Protocol (MCP) server that allows AI assistants like Claude, Cursor, and VS Code to status: experimental. this repository provides a multi-language reference implementation of the proposed interceptor extension for the model context protocol (mcp), as described in sep-1763.
Status: Experimental. This repository provides a multi-language reference implementation of the proposed interceptor extension for the Model Context Protocol (MCP), as described in SEP-1763.
This server falls under the Developer Tools category on MCPgee, the world's largest MCP server directory with 33,000+ servers.
Features
- Status: Experimental. This repository provides a multi-langu
Use Cases
Maintainer
Works with
Installation
Manual Installation
npx experimental-ext-interceptorsConfiguration
Configuration Details
claude_desktop_config.json
Performance
Response Metrics
Resource Usage
How to Set Up and Use Experimental Interceptors
Experimental MCP Interceptors is an early-stage, multi-language reference implementation of the proposed interceptor extension for the Model Context Protocol, as described in the SEP-2624 specification proposal. Interceptors allow developers to insert middleware-like hooks into MCP message flows — inspecting, modifying, or blocking tool calls and responses before they reach their destination. The project is explicitly experimental and intended for feedback and prototyping rather than production use, with implementations planned for C#, Python, TypeScript, and Go.
Prerequisites
- Understanding of the Model Context Protocol (MCP) specification
- Relevant language runtime: .NET SDK for C# (the only in-progress implementation), Node.js 18+ for TypeScript (planned), Python 3.10+ for Python (planned)
- Git to clone the repository
- Familiarity with MCP server development — this is a developer-facing SDK extension, not an end-user tool
Clone the repository
Check out the experimental interceptors repository from the official Model Context Protocol GitHub organization.
git clone https://github.com/modelcontextprotocol/experimental-ext-interceptors.git
cd experimental-ext-interceptorsReview the SEP-2624 specification
Before writing any code, read the specification document included in the repository. Interceptors have specific lifecycle hooks and message format requirements that you must understand to implement them correctly.
Choose your language and check the implementation status
C# is the only in-progress implementation at this time. Python, TypeScript, and Go implementations are planned. Check the repository for the current status of each language before starting.
Add the C# package reference (C# only)
For C# projects, add the interceptors package to your .csproj file. Note the package name from the repository — the library is ModelContextProtocol.Interceptors.
<PackageReference Include="ModelContextProtocol.Interceptors" Version="*-*" />Implement an interceptor
Create a class that implements the interceptor interface to inspect or modify MCP messages. The interceptor receives tool calls and responses and can pass them through, modify them, or block them based on your logic.
Register the interceptor with your MCP server
Wire your interceptor implementation into your MCP server's middleware pipeline using the API provided by the SDK extension. Consult the reference implementation examples in the repository for the exact registration pattern.
Run the CI checks to validate your implementation
The repository uses GitHub Actions for validation. You can trigger all checks on your pull request by commenting '/test all'. Run the test suite locally to verify correctness before submitting feedback.
Experimental Interceptors Examples
Client configuration
Interceptors are an SDK-level extension integrated into your MCP server code, not a standalone server you point a client at. This example shows how a server using interceptors would still be configured in a client config.
{
"mcpServers": {
"my-interceptor-server": {
"command": "dotnet",
"args": ["run", "--project", "/path/to/your/mcp-server-with-interceptors"]
}
}
}Prompts to try
Since this is a developer framework rather than a user-facing server, these are development and validation scenarios rather than end-user prompts.
- "Explain the interceptor lifecycle for MCP tool calls based on SEP-2624."
- "Show me how to write a logging interceptor that records all tool call arguments."
- "How do I block a specific tool call from within an MCP interceptor?"
- "What is the difference between a request interceptor and a response interceptor in MCP?"Troubleshooting Experimental Interceptors
Package ModelContextProtocol.Interceptors cannot be found on NuGet
The package may only be available as a pre-release or direct project reference at this stage of development. Clone the repository and add a local project reference to the C# implementation folder instead of using a NuGet package reference.
Python or TypeScript implementation not available
These implementations are listed as 'Planned' — they do not exist yet. Monitor the repository's README and GitHub issues for status updates, or contribute an implementation based on the C# reference.
Interceptor is registered but does not intercept messages
Ensure your interceptor is registered before the server starts accepting connections, not after. Check that the interceptor is added to the correct pipeline stage (request vs. response) and that the MCP SDK version you are using is compatible with the experimental extension.
Frequently Asked Questions about Experimental Interceptors
What is Experimental Interceptors?
Experimental Interceptors is a Model Context Protocol (MCP) server that status: experimental. this repository provides a multi-language reference implementation of the proposed interceptor extension for the model context protocol (mcp), as described in sep-1763. It connects AI assistants to external tools and data sources through a standardized interface.
How do I install Experimental Interceptors?
Follow the installation instructions on the Experimental Interceptors GitHub repository. Clone the repo, install dependencies, and add the server config to your AI client.
Which AI clients work with Experimental Interceptors?
Experimental Interceptors works with all major MCP-compatible AI clients including Claude Desktop, Claude Code, Cursor, VS Code (GitHub Copilot), Windsurf, and Cline.
Is Experimental Interceptors free to use?
Yes, Experimental Interceptors is open source and available under the Apache-2.0 license. You can use it freely in both personal and commercial projects.
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Set Up Experimental Interceptors in Your Editor
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Quick Config Preview
Add this to your claude_desktop_config.json or .cursor/mcp.json
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