lspmux-cc

Share one rust-analyzer instance across editors, Claude Code, Codex, opencode, and other MCP-capable agents in the same Rust workspace. Built on lspmux by p2502.

How It Works

lspmux multiplexes multiple LSP client connections to one rust-analyzer process. lspmux-cc adds an MCP server that exposes rust-analyzer capabilities as agent-callable tools, plus a Claude Code plugin for transparent LSP routing.

The transport is configurable. TCP loopback is the easiest sandbox-friendly path for agent hosts; Unix sockets remain supported when the host can connect to the socket.

graph LR
    NV[Editor LSP clients<br/>rustaceanvim / Neovim / Vim / VS Code] -->|lspmux client| EP
    CC[Claude Code LSP] -->|plugin lspServers<br/>lspmux client| EP
    MCP[MCP hosts<br/>Claude Code / Codex / opencode / generic MCP] -->|lspmux-cc-mcp<br/>spawns lspmux client| EP
    CLI[lspmux client CLI] --> EP
    EP{{Transport<br/>tcp://127.0.0.1:27631<br/>or Unix socket}}
    EP --> S[lspmux server<br/>spawned on demand]
    S --> RA[rust-analyzer]

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Install

Prerequisites

• macOS or Linux
• Rust toolchain (cargo) for the manual path
• jq
• rust-analyzer available on PATH, via RUST_ANALYZER_PATH, or from the flake package

Install Matrix

Path	Command	What it gives you
Cargo/manual	cargo install --path mcp-server	Installs lspmux-cc-mcp from this checkout.
Cargo/manual	./setup core	Installs or finds lspmux, validates rust-analyzer, writes the lspmux config, and leaves the daemon to be spawned on demand.
Cargo/manual	./setup doctor	Verifies local binaries, config, legacy service state, and Claude Code sandbox hints.
Nix flake	nix build	Builds the default lspmux-cc-mcp package.
Nix flake	nix build .#plugin	Builds the assembled Claude Code plugin with bundled wrappers and pinned binaries.
Nix flake	nix build .#rust-analyzer-nightly	Builds the pinned rust-analyzer package exported by the flake.
Nix flake	nix develop	Enters a shell with lspmux, rust-analyzer, cargo, just, jq, and shell tooling.
Nix flake	nix flake check	Runs the flake checks, including Rust checks, formatting, tests, and plugin structure checks.

./setup core does not install or start a launchd/systemd service. Users upgrading from a pre-M5 install should run ./setup migrate to remove the legacy unit. See docs/migration-m5.md.

Transport

For sandboxed hosts, prefer TCP loopback:

listen = "tcp://127.0.0.1:27631"
connect = "tcp://127.0.0.1:27631"

Then export:

export LSPMUX_CONNECT=tcp://127.0.0.1:27631

Unix sockets are still supported and are the default generated by ./setup core. They are a good fit for unsandboxed editor clients or hosts that can allowlist the exact socket path.

MCP Tools

All tools are read-only: they return data and never modify your files. The edits from rust_code_actions and rust_rename are returned for you or the agent to apply.

Tool	Description	Parameters
rust_diagnostics	Compiler errors and warnings for a file	file_path
rust_hover	Type signature and docs at a position	file_path, line, character
rust_goto_definition	Jump to where a symbol is defined	file_path, line, character
rust_goto_implementation	Implementations of a trait or trait method	file_path, line, character
rust_find_references	All references to a symbol	file_path, line, character
rust_workspace_symbol	Search symbols by name across the workspace	query
rust_document_symbols	A file's hierarchical symbol tree	file_path
rust_code_actions	Quick fixes / refactors for a range, with their edits (unapplied)	file_path, start_line, start_character, end_line, end_character
rust_rename	The workspace edit to rename a symbol (unapplied)	file_path, line, character, new_name
rust_call_hierarchy_incoming	Callers of the symbol at a position	file_path, line, character
rust_call_hierarchy_outgoing	Functions called by the symbol at a position	file_path, line, character
rust_expand_macro	Expand the macro invocation at a position	file_path, line, character
rust_server_status	Server health, readiness, and workspace info	(none)
rust_workspace_registry	All rust-analyzer instances the daemon is hosting	(none)

Coordinates: line and character inputs are zero-based (first line = 0). Output locations are one-based. Subtract 1 from output values before passing them as input to another tool.

All file paths must be absolute.

Host and Editor Integrations

Start with docs/hosts/README.md for the comparison table.

Guide	Use this when
Claude Code	You want both Claude Code LSP routing and MCP tools.
Codex	You want MCP tools in Codex.
opencode	You want opencode MCP tools, optionally with LSP routing.
Generic MCP	You want to wire lspmux-cc-mcp into another MCP host.
rustaceanvim	You use rustaceanvim's built-in lspmux support.
Neovim LSP	You use Neovim's built-in LSP client or nvim-lspconfig.
Vim/vim-lsp	You use Vim 8 with prabirshrestha/vim-lsp.
VS Code	You use the VS Code rust-analyzer extension.

Configuration

Variable	Default	Description
WORKSPACE_ROOT	current directory	Absolute path to the workspace root
LSPMUX_BOOTSTRAP	auto	auto reuses an available daemon or starts one on demand; require fails if unavailable; off skips bootstrap
LSPMUX_PATH	found via PATH or $CARGO_HOME/bin	Path to the lspmux binary
LSPMUX_MCP_PATH	found via PATH, $CARGO_HOME/bin, or result/bin	Path to the lspmux-cc-mcp binary
RUST_ANALYZER_PATH	found via PATH or managed install	Path to the rust-analyzer binary
LSPMUX_CONFIG_PATH	platform default	macOS: ~/Library/Application Support/lspmux/config.toml; Linux: $XDG_CONFIG_HOME/lspmux/config.toml
LSPMUX_CONNECT	config connect value	Explicit lspmux client endpoint override. Accepts Unix socket paths, host:port, or tcp://host:port.
LSPMUX_SOCKET_PATH	$XDG_RUNTIME_DIR/lspmux/lspmux.sock	Legacy endpoint override. Still accepted for compatibility, but LSPMUX_CONNECT is preferred.

LSPMUX_PATH, LSPMUX_MCP_PATH, and RUST_ANALYZER_PATH sit at the top of their lookup cascades, so a stale export shadows an installed or bundled binary. See docs/binary-resolution.md for the full resolution order of each binary.

Project Layout

config/                       # lspmux.toml template
docs/                         # host integration guides, brainstorms
launchd/                      # legacy macOS service template
mcp-server/                   # Rust MCP server (the main binary)
  src/
    main.rs                   # entry point
    bootstrap.rs              # runtime config, service discovery
    lsp_client.rs             # LSP JSON-RPC client
    tools.rs                  # MCP tool definitions
  tests/
    integration.rs            # multi-client sharing test
bin/                          # wrapper scripts (lspmux, lspmux-cc-mcp, rust-analyzer)
hooks/                        # session-start, post-file-edit
skills/                       # tool documentation & diagnostics
.claude-plugin/               # plugin manifest + marketplace metadata
.mcp.json                     # MCP server config
.lsp.json                     # LSP server config
setup                         # installation script
systemd/                      # legacy Linux service template
todos/                        # tracked issues and roadmap

Development

just check       # cargo check
just build       # cargo build
just clippy      # pedantic + nursery lints
just fmt         # cargo fmt
just test        # cargo test
just shellcheck  # lint shell scripts
just pre-push    # check + clippy + fmt-check + test

nix flake check  # clippy + fmt + tests via Nix
nix build        # build mcp-server binary
nix develop      # enter devShell

License

MIT