MCP Plexus

MCP Plexus is a high‑performance, multi‑tenant framework that builds upon the FastMCP 2.7 core to give developers a turnkey solution for deploying secure, scalable Model Context Protocol servers. It addresses the growing need for isolated AI backends that can safely expose custom toolsets, resources, and prompts to large language models while managing external API access in a unified way.

At its core, Plexus solves the problem of tenant isolation and credential management. By routing requests through tenant‑specific URL paths, each client or organization can operate in a sandboxed environment with its own session store (currently Redis) and tool visibility. This eliminates the risk of cross‑tenant data leakage and simplifies compliance with data‑privacy regulations. The framework also provides a dedicated user registration endpoint that links host application users to persistent Plexus identities, enabling seamless storage of OAuth 2.1 tokens and API keys that are scoped to individual users rather than the server itself.

The platform’s most powerful feature is its built‑in OAuth 2.1 flow for external services. Developers can annotate MCP tools with a decorator, and Plexus automatically handles the Authorization Code Grant with PKCE, token exchange, refresh logic, and secure storage. This means a tool can call GitHub, Google Drive, or any OAuth‑protected API without embedding credentials in the codebase. When a user authenticates once, their token is cached and reused across subsequent tool invocations, dramatically improving the end‑user experience.

In addition to secure integrations, Plexus offers a clean, decorator‑based API for defining tools, resources, prompts, and sampling strategies. Because it leverages FastMCP’s proven performance engine, developers can focus on business logic rather than protocol plumbing. The framework also leaves room for future extensions—custom authentication providers, tenant‑specific configuration overrides, and advanced session management are all planned.

Real‑world scenarios that benefit from MCP Plexus include SaaS platforms that need to expose AI assistants to multiple customers, enterprise systems integrating LLMs with internal APIs, and research labs building isolated experimental environments. By combining multi‑tenancy, secure credential handling, and a developer‑friendly API, Plexus enables teams to deliver robust AI services at scale without compromising security or maintainability.