The binary

Binary

mcpx ships as one Go binary, built from cmd/mcpx. This page states what is shipped — what the binary contains, what it needs next to it, and how the two packaged forms are built — not what could be built. Where a fact changes per release channel, this page says so and stops; release and install channels are a different page’s subject.

What is in it

The version is 0.1.0, hard-coded as the default in cmd/mcpx/main.go and stamped by the package with -X main.version=0.1.0; a build may override it with the same -ldflags variable, and nothing else about the binary changes.

Everything else is the module’s direct dependencies. go.mod is the source of truth — seven direct requirements:

The three charmbracelet modules are one decision: about 1.2 MB in the stripped binary, in exchange for not hand-writing terminal handling. dependencies.md argues each of the original five in full; it and package.nix still say “five” because both predate the last two rows — trust go.mod, and this table, over that count.

Two absences are as deliberate as the presences:

• No MCP SDK. mcpx is built on none — there is no MCP module in go.mod. The MCP client (internal/mcpclient), the server (internal/mcpserver) and the JSON-RPC framing are mcpx’s own code, about a package each. That is most of why the dependency list stays this short.
• Everything else is the standard library: the daemon and its HTTP API, the process pools, the JSON Schema to TypeScript compiler, the CLI.

How the shipped builds link

Every direct dependency is pure Go, so a CGO_ENABLED=0 build is fully static, and that is what the Nix package ships: env.CGO_ENABLED = "0" in package.nix, stripped (-s -w), so the shipped binary is a static executable that needs no libc next to it.

The container image makes the other choice, on purpose for now: its Containerfile defaults CGO_ENABLED to 1, so the binary it ships links glibc and the runtime stage is Debian bookworm-slim. A static container build was measured working end-to-end before that default was chosen — see container.md, which this page links rather than restates, because the container is still changing.

The behavioural difference between the two is narrow and worth stating exactly: with cgo off, pure-Go os/user reads /etc/passwd rather than asking NSS/LDAP, and the pure-Go resolver bypasses NSS modules — on Linux only; on macOS, CGO_ENABLED=0 changes neither, because Go uses the system resolver and user database there without cgo either way. Neither difference prevents a static build, and this page never claims they do; which form to ship where is a policy question, tracked with the release work, not a technical block.

Size, as last measured in container.md: the mcpx binary is about 14.8 MB in the container build. (The 21 MB figure sometimes quoted is an older linux/arm64 static build; measure the artifact you are shipping, not either number here.)

What it needs next to it

The binary alone answers ls, types, catalog, search and call. The rest of what it reaches for is external programs — the full table, with what degrades when each is missing, is in dependencies.md:

• A JavaScript runtime — deno, bun or node — for mcpx run and mcpx exec only. Without one, those two commands fail and everything else still works.
• git — a fallback only. mcpx reads .git itself for the repo and worktree scopes (see git-discovery.md) and runs git rev-parse only for a repository layout its own reader does not vouch for. Without git, those rare layouts degrade to keying by directory, and mcpx doctor says why.
• The configured MCP servers themselves — spawned with the command, args, env and cwd the config names, or reached over Streamable HTTP for url servers.

The Nix package wraps the binary with a PATH suffix naming git, deno, bun-bin and nodejs, so those four are findable without depending on the calling shell — and because it is a suffix, a runtime already on your PATH wins over the wrapped one. The same package installs the generated man page and shell completions (see the CLI page).

The container image ships exactly one runtime — bun — and sets MCPX_SCRIPT_RUNTIME=bun, so the runtime choice inside the image is unambiguous; it leaves git out entirely, for the reason above. What the image deliberately does not contain, and why, is container.md’s subject.