MCP Integration

Unified MCP Endpoint

All MCP tool calls go through a single endpoint: POST /v1/mcp. The gateway routes calls to the correct MCP server using the tool name prefix (server_name/tool_name) or semantic matching.

The endpoint speaks JSON-RPC 2.0 and supports tools/list, tools/call, and resources/read.

Use a virtual key of type mcp or all — an llm-only key is refused with 403 key_type_mismatch. Note the /v1 prefix: a bare POST /mcp is a legacy alias that does not reach the gateway on deployments where the control plane shares the hostname, so always point clients at /v1/mcp.

Client Configuration

Argus uses the standard MCP HTTP+SSE transport. Any client that supports MCP can connect — here are configuration examples for popular tools.

// .mcp.json (Claude Code)
{
  "mcpServers": {
    "nexus": {
      "url": "https://nexus.cirruslabs.technology/v1/mcp",
      "headers": {
        "Authorization": "Bearer nxvk_your_virtual_key"
      }
    }
  }
}

// claude_desktop_config.json (Claude Desktop)
{
  "mcpServers": {
    "nexus": {
      "command": "npx",
      "args": ["-y", "mcp-remote", "https://nexus.cirruslabs.technology/v1/mcp"]
    }
  }
}

// Cursor Settings > MCP Servers > Add Server
// Type: SSE
// URL: https://nexus.cirruslabs.technology/v1/mcp
// Headers:
//   Authorization: Bearer nxvk_your_virtual_key

// Windsurf Settings > MCP
{
  "mcpServers": {
    "nexus": {
      "serverUrl": "https://nexus.cirruslabs.technology/v1/mcp",
      "headers": {
        "Authorization": "Bearer nxvk_your_virtual_key"
      }
    }
  }
}

// .continue/config.yaml
mcpServers:
  - name: nexus
    url: https://nexus.cirruslabs.technology/v1/mcp
    headers:
      Authorization: Bearer nxvk_your_virtual_key

// Any MCP client supporting HTTP+SSE transport
{
  "url": "https://nexus.cirruslabs.technology/v1/mcp",
  "transport": "sse",
  "headers": {
    "Authorization": "Bearer nxvk_your_virtual_key"
  }
}

Listing Available Tools

Discover all tools available to your virtual key:

curl -X POST https://nexus.cirruslabs.technology/v1/mcp \
  -H "Authorization: Bearer nxvk_your_virtual_key" \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "tools/list",
    "id": 1
  }'

Calling a Tool

Call a specific tool by its full name (server_name/tool_name):

curl -X POST https://nexus.cirruslabs.technology/v1/mcp \
  -H "Authorization: Bearer nxvk_your_virtual_key" \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "tools/call",
    "params": {
      "name": "server_name/tool_name",
      "arguments": { "param1": "value1" }
    },
    "id": 2
  }'

Agentic Tool Loop

Add the x-argus-mcp: true header to chat completion requests. The gateway will automatically execute MCP tools when the model requests them, feeding results back until the model produces a final response. This works with any model that supports tool use.

curl -X POST https://nexus.cirruslabs.technology/v1/chat/completions \
  -H "Authorization: Bearer nxvk_your_virtual_key" \
  -H "Content-Type: application/json" \
  -H "x-argus-mcp: true" \
  -d '{
    "model": "claude-sonnet-4-6",
    "messages": [{"role": "user", "content": "Search for recent PRs"}]
  }'

Tool Discovery

The Argus MCP gateway uses a three-tier tool resolution strategy:

1. 1.Exact match — if the tool name includes a server prefix (server/tool), route directly
2. 2.Direct name match — an unprefixed name that matches a tool on exactly one registered server routes there. If several servers expose the same name, the first is used
3. 3.Semantic search — match the tool description against the request using embeddings. Below a similarity of 0.65 nothing matches; at or above 0.88 the top candidate is used directly. In between, if two or more candidates fall within 0.05 of the top score, an LLM reranker picks among them

Built-in Native Tools

The Argus MCP gateway includes 13 built-in tools that are always available — no external server setup required. These tools provide access to the Argus prompt library, context store, persistent memory, and gateway management.

These tools are visible in the MCP Explorer under Argus Gateway and are included in every tools/list response. Any connected MCP client (Claude Code, Cursor, etc.) can use them immediately.