MCP Protocol

The MCP (Model Context Protocol) plugin has two distinct sides:

  1. MCP Client (discovery) — point Bowire at any MCP server URL, browse its tools / resources / prompts, and invoke them. Analogous to the gRPC and REST plugins.
  2. MCP Adapter (opt-in feature) — expose Bowire's discovered API services as MCP tools so AI agents (Claude, Copilot, Cursor) can call your gRPC / REST / SignalR methods. Disabled by default to prevent silently exposing an internal API surface.

Package: Kuestenlogik.Bowire.Protocol.Mcp

MCP Client — discovering an external MCP server

Standalone:

bowire --url http://localhost:5003/mcp

The URL you supply is the MCP message endpoint itself. The plugin uses the streamable HTTP transport: it POSTs JSON-RPC requests directly to that URL and reads the response (either application/json or text/event-stream framing). No /sse event stream is required.

After the handshake (initialize + notifications/initialized), Bowire calls tools/list, resources/list, and prompts/list and surfaces each non-empty category as its own service in the sidebar:

Service Methods Invocation
Tools one per discovered tool tools/call with the tool arguments
Resources one per resource (method name = URI) resources/read
Prompts one per prompt prompts/get with the prompt arguments

Tool input schemas (inputSchema, JSON Schema with type: "object") are mapped to the standard form-based UI: strings become text inputs, numbers become number fields, booleans become checkboxes, arrays become repeated fields, and nested objects become message fields. Required fields are marked with an asterisk.

Sample target

Bowire.Samples/SimpleMcp is a hand-rolled JSON-RPC 2.0 MCP server (no Bowire / no gRPC dependency) running on port 5003. It exposes:

  • Tools — echo, add, weather
  • Resources — notes://welcome, notes://changelog
  • Prompts — greet (with name and optional language arguments)

Run it and point Bowire at it:

dotnet run --project src/SimpleMcp
bowire --url http://localhost:5003/mcp

Transport notes

The plugin supports the modern MCP streamable HTTP transport (MCP 2025-03-26): a single endpoint that accepts POSTed JSON-RPC requests and returns either application/json or framed text/event-stream. The older SSE+POST split is not supported.

MCP Adapter — exposing Bowire as an MCP server

The adapter goes the other direction: it wraps every service Bowire can discover (gRPC, REST, SignalR) as an MCP tool. AI agents connect to Bowire as if it were an MCP server, list the tools, and invoke them — the adapter dispatches each call to the matching protocol plugin.

This is opt-in because it would otherwise expose any API the host happens to discover.

Embedded mode — WithMcpAdapter() chained on MapBowire()

using Kuestenlogik.Bowire;
using Kuestenlogik.Bowire.Protocol.Mcp;

app.MapBowire(options => options.Title = "My API")
   .WithMcpAdapter("https://localhost:5005");

The .WithMcpAdapter() extension only exists when the Kuestenlogik.Bowire.Protocol.Mcp package is referenced — projects that don't depend on it cannot accidentally activate the adapter.

Standalone mode — --enable-mcp-adapter flag

bowire --url https://localhost:5005 --enable-mcp-adapter

Without the flag, bowire runs as an MCP client only. With it, the adapter is mapped at /bowire/mcp/sse + /bowire/mcp/message.

Adapter endpoints

Endpoint Description
POST /{prefix}/mcp MCP streamable HTTP transport (MCP 2025-03-26): a single endpoint, JSON-RPC 2.0 in, JSON out. Handles initialize, tools/list, tools/call, ping. This is what bowire --url should target.

The legacy SSE+POST split (/sse event stream + /messages POST) from the older MCP 2024-11-05 spec is intentionally not supported here.

Agent configuration

Claude Desktop (claude_desktop_config.json):

{
  "mcpServers": {
    "bowire": {
      "url": "http://localhost:5080/bowire/mcp/sse"
    }
  }
}

Cursor uses the same mcpServers shape. Other MCP clients accept either the SSE URL or the message endpoint URL directly.

Tool naming

Each discovered method becomes one tool: {service-name-with-underscores}_{method}. For example, calculator.CalculatorService/Add becomes calculator_CalculatorService_Add. Tool input schemas are derived from the discovered BowireMessageInfo (protobuf for gRPC, CLR types for REST/SignalR).

Only unary methods are exposed — streaming methods don't fit MCP's request/response shape.

Security warning

Enabling the adapter lets any MCP client invoke any discovered API method. Don't use it on a server whose API surface should not be reachable from arbitrary local MCP clients. The adapter is intended for development-time AI integration, not production exposure.

Sample

Bowire.Samples/SimpleMcpAdapter is a gRPC CalculatorService with the adapter chained in:

app.MapBowire(options => options.Title = "Simple MCP Adapter")
   .WithMcpAdapter("https://localhost:5005");

Run it on port 5005 and Bowire standalone can browse it both ways:

bowire --url https://localhost:5005               # gRPC reflection
bowire --url https://localhost:5005/bowire/mcp   # MCP client

See also: Quick Start, Plugin System

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