Callmux

AI agents make tool calls one at a time. Creating 10 GitHub issues? That's 10 sequential round-trips. Fetching data from 3 different servers? 3 serial waits.

callmux sits between your agent and any MCP server, adding capabilities the original doesn't have:

Why Tool Call Reduction Matters

Every tool call adds structural overhead (~75 tokens) and intermediate reasoning (~150 tokens of "Now I'll fetch the next one...") to your context window. Batch 7 calls into 1 and you eliminate ~1,350 tokens of pure waste, a 19:1 reduction in context pollution. Since context is cumulative (every turn re-processes everything before it), this compounds across a session.

In practice, callmux reduces tool calls to ~15% of the original count. Sessions run longer before compaction, cost less in API tokens, and produce better output because the model isn't re-reading filler from 40 turns ago.

Full breakdown of the context math with diagrams

Install

No install needed. Use npx:

npx -y callmux -- npx -y @modelcontextprotocol/server-github

Or install globally:

npm install -g callmux

Quick Start

Add to ~/.claude.json or project .mcp.json (Claude Code):

{
  "mcpServers": {
    "github": {
      "command": "npx",
      "args": ["-y", "callmux", "--", "npx", "-y", "@modelcontextprotocol/server-github"]
    }
  }
}

Done. Claude now sees all GitHub tools plus the callmux_* meta-tools.

Works with any MCP client: Codex, Claude Desktop, Cursor, Windsurf, and anything that speaks MCP stdio or HTTP. The interactive setup wizard handles configuration for you.

Key Features

Shared Server: 60 Processes Down to 6

Run callmux once, connect all sessions. One set of downstream servers, shared cache, no orphaned processes. On a machine with 6 agent sessions and 5 MCP servers, that's ~60 processes and 4+ GB RAM collapsed to ~6 processes and ~500 MB.

callmux --listen 4860
callmux daemon install --start --enable

Full guide ->

Resilient Bridge: Sessions That Survive Restarts

Codex users know the pain: when an MCP server restarts or loses its transport, the entire Codex session needs to restart to reconnect. callmux's stdio bridge sits between Codex and the shared listener. If the listener hiccups, the bridge reconnects and retries on the next tool call. The agent session never notices.

[mcp_servers.callmux]
command = "callmux"
args = ["bridge", "--url", "http://localhost:4860/mcp"]

Full guide ->

Meta-Only Mode: Fixed System Prompt Size

50+ tool definitions bloat the system prompt on every API turn, costing tokens that compound across the session. Meta-only mode hides all downstream tools and exposes only 11 meta-tools. The agent discovers tools via callmux_search_tools or callmux_status and calls them through callmux_call. System prompt size stays fixed regardless of how many servers you add.

Full guide ->

Enterprise Security Built In

Authentication (scrypt-hashed bearer tokens, OIDC JWT), role-based access control, rate limiting, CIDR allowlists, structured audit logging, and Prometheus metrics. Shared listeners hot-reload config-file changes and still support SIGHUP reloads. Hardened defaults: non-loopback listeners refuse to start without auth.

Full guide ->

Read-Only Dashboard: Live Runtime Visibility

Optional dashboard for shared listeners. Disabled by default, then enabled with dashboard.enabled. It shows server health, active sessions, cache and response-store stats, recent tool calls, tool-suite changes, config reloads, and errors.

Full guide ->

Recipes: Team Workflows as Callable Names

Define multi-step operations once in config, call them by name from any agent session. Encode team conventions (bug issues always get the bug label), triage workflows (fetch two issues in parallel for comparison), or analysis pipelines (search then analyze). One name, consistent execution, works across all clients.

Full guide ->

Tool Scoping: Per-Server Filtering for Any Client

Whitelist which tools each server exposes. This gives any MCP client per-server tool filtering, even clients that don't support it natively (Codex, Cursor, Windsurf).

callmux server add github --tools "create_issue,get_issue,list_issues" -- npx -y @modelcontextprotocol/server-github

Meta-Tools

These tools are exposed to your agent alongside (or instead of) the proxied tools:

All argument objects support file references ($file, $jsonFile, $yamlFile, $text) for long content that doesn't belong in JSON strings.

Interactive Setup

The fastest way to go from zero to configured:

npx -y callmux setup

The wizard detects existing MCP servers, lets you pick from a curated list or add custom ones, auto-discovers tools via probing, configures caching, offers meta-only mode, and attaches to your client (Claude Code, Codex) automatically.

Documentation

Related

• tokenlean - CLI tools for AI agents, token-efficient code understanding. Same philosophy: make agents less wasteful.

License

MIT