45f9e0ef27C# implementation of SEP-1763 --------- Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
115 lines
3.2 KiB
Markdown
115 lines
3.2 KiB
Markdown
# MCP Interceptors C# SDK
|
|
|
|
This library provides interceptor support for the Model Context Protocol (MCP) .NET SDK. Interceptors enable validation, mutation, and observation of MCP messages without modifying the original server or client implementations.
|
|
|
|
## Overview
|
|
|
|
MCP Interceptors (SEP-1763) allow you to:
|
|
|
|
- **Validate** incoming requests before they reach handlers
|
|
- **Mutate** requests or responses to transform data
|
|
- **Observe** message flow for logging, metrics, or auditing
|
|
|
|
Interceptors can be deployed as:
|
|
- Sidecars alongside MCP servers
|
|
- Gateway services that proxy MCP traffic
|
|
- Embedded validators within applications
|
|
|
|
## Installation
|
|
|
|
```bash
|
|
dotnet add package ModelContextProtocol.Interceptors
|
|
```
|
|
|
|
## Quick Start
|
|
|
|
```csharp
|
|
using Microsoft.Extensions.DependencyInjection;
|
|
using Microsoft.Extensions.Hosting;
|
|
using ModelContextProtocol.Interceptors;
|
|
|
|
var builder = Host.CreateApplicationBuilder(args);
|
|
|
|
builder.Services.AddMcpServer()
|
|
.WithStdioServerTransport()
|
|
.WithInterceptors<ParameterValidator>();
|
|
|
|
await builder.Build().RunAsync();
|
|
```
|
|
|
|
## Creating an Interceptor
|
|
|
|
```csharp
|
|
using ModelContextProtocol.Interceptors;
|
|
using ModelContextProtocol.Interceptors.Server;
|
|
using System.Text.Json.Nodes;
|
|
|
|
[McpServerInterceptorType]
|
|
public class ParameterValidator
|
|
{
|
|
[McpServerInterceptor(
|
|
Name = "parameter-validator",
|
|
Description = "Validates tool call parameters",
|
|
Events = new[] { InterceptorEvents.ToolsCall },
|
|
Phase = InterceptorPhase.Request)]
|
|
public ValidationInterceptorResult ValidateToolCall(JsonNode? payload)
|
|
{
|
|
if (payload is null)
|
|
{
|
|
return new ValidationInterceptorResult
|
|
{
|
|
Valid = false,
|
|
Severity = ValidationSeverity.Error,
|
|
Messages = [new() { Message = "Payload is required" }]
|
|
};
|
|
}
|
|
|
|
return new ValidationInterceptorResult { Valid = true };
|
|
}
|
|
}
|
|
```
|
|
|
|
## Interceptor Types
|
|
|
|
### Validation Interceptors
|
|
Validate requests/responses and return pass/fail results with optional error messages.
|
|
|
|
### Mutation Interceptors
|
|
Transform request or response payloads before they continue through the pipeline.
|
|
|
|
### Observability Interceptors
|
|
Observe message flow for logging, metrics collection, or auditing without modifying data.
|
|
|
|
## Configuration Options
|
|
|
|
### Phase
|
|
- `InterceptorPhase.Request` - Intercept incoming requests
|
|
- `InterceptorPhase.Response` - Intercept outgoing responses
|
|
- `InterceptorPhase.Both` - Intercept both directions
|
|
|
|
### Events
|
|
Interceptors can target specific MCP events:
|
|
- `InterceptorEvents.ToolsCall` - Tool invocation requests
|
|
- `InterceptorEvents.PromptGet` - Prompt retrieval
|
|
- `InterceptorEvents.ResourceRead` - Resource access
|
|
- And more...
|
|
|
|
### Priority
|
|
Use `PriorityHint` to control interceptor execution order (lower values run first).
|
|
|
|
## Sample Projects
|
|
|
|
See the `samples/InterceptorServiceSample` directory for a complete example of a security-focused validation interceptor.
|
|
|
|
## Requirements
|
|
|
|
- .NET 8.0 or later (or .NET Standard 2.0 compatible runtime)
|
|
- ModelContextProtocol SDK 0.1.0-preview.10 or later
|
|
|
|
## License
|
|
|
|
MIT License - see LICENSE file for details.
|
|
|
|
## Contributing
|
|
|
|
Contributions are welcome! Please see the FSIG CONTRIBUTING.md for guidelines.
|