MCP

This guide covers the NEXUS local MCP server, which exposes the app running on your machine to MCP clients. It is separate from connecting an external MCP server to Chainabit and exposing Chainabit as an MCP server. For several CLI coding agents NEXUS hosts, it writes the connection entry automatically; see Automatic wiring.

What you get

Ten tool families, discovered together on one connection:

• canvas_* — read and write the shared canvas.
• agent_* — list mesh peers, originate tasks on other agents, invite an agent into a channel, request a new agent, and read or update agent identity.
• window_* — read window state and what is attached to a window.
• memory_* — one shared, durable memory across every connected client.
• provider_* — the AI provider registry and bridge runtime facts.
• team_* — team membership.
• neural_* — bounded traversal of the Neural Map.
• browser_* — observe and automate a NEXUS browser Window.
• workspace_* — read which workspace an agent is scoped to, and how that resolved.
• tool_* — read this catalog annotated with your own live permissions.

Most families are workspace-scoped, canvas writes require an explicit role grant (see Canvas Roles), and every write is subject to the calling agent's autonomy mode.

One server among two

Every tool description this server returns begins with [Local NEXUS app]. If you also have the Chainabit cloud MCP server connected, some tool names overlap and some concepts — "agent", "memory", "workspace" — exist separately on both, with no relationship between them. NEXUS local MCP vs Chainabit cloud MCP explains how to tell which server you are talking to.

How the connection works, briefly

The server runs locally, speaks newline-delimited JSON-RPC 2.0 over stdio, and opens no network port. It supports two protocol eras at once — a 2025-06-18-style initialize handshake, and a handshake-free 2026-07-28 style that uses server/discover and a _meta block on every request. Protocol Eras covers picking one and handling a mismatch; the field-by-field contract is in MCP Protocol.

In this guide

• Connect a Client — declaring the server as a stdio entry in a CLI's own configuration.
• Protocol Eras — the dual-era negotiation, and what a version mismatch looks like.
• Tool Namespaces — how the ten families sit together on one server.
• NEXUS local MCP vs Chainabit cloud MCP — two servers, two planes, and the collisions between them.
• Troubleshooting — failed discovery, version mismatch, and credential problems on the wire.

Where to go next

• Getting Started — install and connect for the first time.
• How to expose NEXUS to a CLI — the exact steps to point a CLI agent at the server.
• MCP Protocol — transport, version negotiation, and error shapes.
• MCP Tools — every tool, what it does, and what it returns.
• Tutorials — an end-to-end walkthrough.