Concepts

Core concepts behind Argus MCP - the gateway model, backends, transports, and middleware pipeline.

What is Argus MCP?

Argus MCP is a gateway server for the Model Context Protocol (MCP). Instead of connecting your AI client directly to each MCP tool server, you point the client at a single Argus endpoint. Argus handles discovery, routing, and lifecycle management for all of your backends.

Backends

A backend is any MCP-compliant tool server that Argus connects to. Backends can communicate over different transports:

  • stdio — Argus spawns the backend as a child process and communicates over stdin/stdout. This is the most common type for local tool servers.
  • SSE — Argus connects to an already-running backend over Server-Sent Events.
  • Streamable HTTP — Argus connects to a backend using the newer Streamable HTTP transport.

You declare backends in config.yaml. Argus connects to all of them at startup and aggregates their tools, resources, and prompts into a single namespace.

The Gateway

The gateway is the core of Argus. It sits between your MCP client and the backends, providing:

  • Aggregation — All tools from all backends appear as a single flat list to the client.
  • Transport bridging — The client connects over SSE or Streamable HTTP regardless of how each backend communicates.
  • Hot reload — Add, remove, or reconfigure backends without restarting the server.
  • Health monitoring — Argus tracks the health of each backend and can surface status through the management API and TUI.

Middleware Pipeline

Every request that flows through Argus passes through a middleware pipeline. Middleware can inspect, transform, or reject requests before they reach a backend. Built-in middleware includes:

  • Authentication — Validate client tokens (Bearer, API key, or custom headers).
  • Rate limiting — Per-client or global rate limits on tool calls.
  • Logging and telemetry — Structured request/response logging with OpenTelemetry integration.
  • RBAC — Role-based access control that restricts which tools a client can invoke.

Middleware is configured declaratively in config.yaml and executes in the order it is declared.

Container Isolation

When Docker or Podman is available, Argus can automatically run each stdio backend inside a hardened container. This provides:

  • Sandboxing — Each backend runs in its own isolated filesystem and network namespace.
  • Reproducibility — Container images are built from the backend's declared dependencies.
  • Zero config — Isolation is enabled by default when a container runtime is detected.

Management API and TUI

Argus exposes a management REST API at /manage/v1/ for programmatic control: listing backends, checking health, hot-reloading config, and more.

The TUI (Terminal User Interface) provides a visual dashboard for monitoring backends, inspecting tools, and invoking tool calls interactively. It connects to the management API over HTTP, so it can run locally or against a remote Argus instance.

Next Steps