MCP Server

Polecat ships with a built-in Model Context Protocol (MCP) server that exposes your event store configuration as read-only tools. This lets AI assistants and agents introspect your Polecat setup for diagnostics, code generation guidance, and operational visibility.

The MCP server uses the Streamable HTTP transport (stateless POST-based JSON-RPC) and is implemented as ASP.NET Core Minimal API endpoints in the Polecat.AspNetCore package.

Installation

Install the Polecat.AspNetCore NuGet package:

dotnet add package Polecat.AspNetCore

Setup

Register the MCP endpoints in your ASP.NET Core application:

using Polecat.AspNetCore;

var app = builder.Build();

app.MapPolecatMcp();

This registers a single POST endpoint at /polecat/mcp/ that handles all MCP JSON-RPC requests.

Custom Route Prefix

You can change the default route prefix:

app.MapPolecatMcp("/api/polecat-mcp");

Authorization

MapPolecatMcp() returns a RouteGroupBuilder, so you can chain standard ASP.NET Core endpoint configuration including authorization policies:

app.MapPolecatMcp()
    .RequireAuthorization("AdminPolicy");

Or with a specific authorization policy:

app.MapPolecatMcp()
    .RequireAuthorization(policy =>
    {
        policy.RequireRole("admin");
    });

WARNING

The MCP endpoints expose internal configuration details about your event store schema, projections, and event types. You should apply authorization to these endpoints in production environments.

Available Tools

The MCP server exposes three read-only tools:

get_event_store_configuration

Returns the full event store options snapshot including:

Property	Description
streamIdentity	AsGuid or AsString
tenancyStyle	Single or Conjoined
databaseSchemaName	Schema for event tables
enableCorrelationId	Correlation ID tracking enabled
enableCausationId	Causation ID tracking enabled
enableHeaders	Custom event headers enabled

list_known_event_types

Lists all event types registered with the event store. Each entry includes:

Property	Description
eventTypeName	The alias stored in the database type column (e.g. members_joined)
dotNetTypeName	The full .NET type name

list_projections

Lists all projections and subscriptions. Each entry includes:

Property	Description
name	Projection class name
implementationType	Full .NET type name
type	Subscription type (e.g. Snapshot, MultiStream, FlatTableProjection)
shards	Array of shard identifiers

MCP Protocol Details

The endpoint implements the MCP Streamable HTTP transport. All requests are JSON-RPC 2.0 POST requests to the single endpoint.

Supported Methods

Method	Description
initialize	Handshake — returns server capabilities
tools/list	Lists available tools with descriptions and input schemas
tools/call	Executes a tool by name and returns results

Example Request

curl -X POST http://localhost:5000/polecat/mcp/ \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "tools/call",
    "params": { "name": "get_event_store_configuration" }
  }'

Example Response

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "content": [
      {
        "type": "text",
        "text": "{\"streamIdentity\":\"AsGuid\",\"tenancyStyle\":\"Single\",\"databaseSchemaName\":\"dbo\",...}"
      }
    ]
  }
}