Nereid MCP Server

Nereid is a terminal-first workspace for Mermaid-backed diagrams. It combines a `ratatui` TUI, a Model Context Protocol (MCP) server, folder-based

Local serverstdio

What is the Nereid MCP server?

Nereid MCP server is a locally run integration for AI assistants that speak the Model Context Protocol. Nereid is a terminal-first workspace for Mermaid-backed diagrams. It combines a ratatui TUI, a Model Context Protocol (MCP) server, folder-based session persistence, and deterministic text renders so humans and AI agents can inspect and.

What the assistant can call

Once Nereid is connected, these are the calls the assistant has available:

  • Optional — VISUAL or EDITOR for the in-app Mermaid editor. Nereid falls back to vi
  • Walkthroughs — walkthrough_list, walkthrough_current, walkthrough_open, walkthrough_read, walkthrough_stat, walkthrough_get_node, walkthrough_render_text
  • Cross — references and objects: xref_list, xref_neighbors, xref_add, xref_remove, object_read
  • Queries — route_find, seq_messages, seq_search, seq_trace, flow_reachable, flow_paths, flow_cycles, flow_unreachable, flow_dead_ends, flow_degrees
  • Task — Command
  • Path — Purpose
  • nereid-session.meta.json — Session id, active diagram and walkthrough ids, diagram index, xrefs, and selection state
  • Key — Action
  • Space — Toggle selected object
  • Prerequisites — Installing Nereid does not grant unrestricted rights. The same source-available noncommercial license applies to crates.io, Homebrew, GitHub
  • Cargo — The Cargo tool exposed by this server
  • Homebrew — The Homebrew tool exposed by this server

Configuration and credentials

  • Rust 1.85 or newer when installing with Cargo or building from source. - A terminal that supports alternate-screen TUI applications. - Optional: VISUAL or EDITOR for the in-app Mermaid editor. Nereid falls back to vi. Installing Nereid does not grant unrestricted rights. The same source-available noncommercial license applies to crates.io, Homebrew, GitHub Releases, npm, Docker, and

Setting it up

@bnomei/nereid on npm is all you need. Most clients run it directly, so configuration is a few lines and a restart.

Choosing this one

Among the cloud and infrastructure options, the useful question is rarely "what can it do" but "what does it cost you to run" — permissions, credentials, and how much of your context its toolset consumes. Nereid's toolset — Optional, Walkthroughs, Cross and 9 more — is a fair guide to whether it matches your workflow. It is maintained by bnomei; worth a glance at recent repository activity before you build anything load-bearing on it.

SyncDev reviews every entry in this directory against the project's own documentation before publishing, and revisits them as servers change.

Before you rely on it

  • It runs with your machine's permissions. That is convenient and also the reason to think about what you point it at before you approve a tool call.
  • With 12 tools registered it takes up a noticeable share of the context window; turn it off in projects that never touch Nereid.
  • MCP clients confirm each tool call by default. Leave that on until you have watched what the nereid mcp server does with a few real requests.

Available tools

ToolWhat it does
OptionalVISUAL or EDITOR for the in-app Mermaid editor. Nereid falls back to vi.
Walkthroughswalkthrough_list, walkthrough_current, walkthrough_open, walkthrough_read, walkthrough_stat, walkthrough_get_node, walkthrough_render_text, walkthrough_diff, walkthrough_apply_ops.
Crossreferences and objects: xref_list, xref_neighbors, xref_add, xref_remove, object_read.
Queriesroute_find, seq_messages, seq_search, seq_trace, flow_reachable, flow_paths, flow_cycles, flow_unreachable, flow_dead_ends, flow_degrees.
TaskCommand
PathPurpose
nereid-session.meta.jsonSession id, active diagram and walkthrough ids, diagram index, xrefs, and selection state.
KeyAction
SpaceToggle selected object.
PrerequisitesInstalling Nereid does not grant unrestricted rights. The same source-available noncommercial license applies to crates.io, Homebrew, GitHub Releases, npm, Docker, and source builds.
CargoThe Cargo tool exposed by this server.
HomebrewThe Homebrew tool exposed by this server.

How to install the Nereid MCP server

{
  "mcpServers": {
    "nereid": {
      "command": "npx",
      "args": ["-y", "@bnomei/nereid"]
    }
  }
}

Add to claude_desktop_config.json, then restart Claude Desktop.

Configuration

  • Rust 1.85 or newer when installing with Cargo or building from source. - A terminal that supports alternate-screen TUI applications. - Optional: VISUAL or EDITOR for the in-app Mermaid editor. Nereid falls back to vi. Installing Nereid does not grant unrestricted rights. The same source-available noncommercial license applies to crates.io, Homebrew, GitHub Releases, npm, Docker, and

Example prompts to try

  • Use Nereid to Optional.
  • Use Nereid to Walkthroughs.
  • Use Nereid to Cross.

Frequently asked questions

It connects Nereid to MCP-compatible AI assistants such as Claude and Cursor, exposing 12 tools (Optional, Walkthroughs, Cross, and more) that the assistant can call on your behalf. Instead of copying data back and forth by hand, the assistant works with Nereid directly.