fold

fold: the enterprise MCP gateway — one governed endpoint between every MCP client and every MCP server.

fold sits in front of any number of upstream MCP servers — in any language, on any SDK, from any team or vendor — providing federation, enterprise auth, policy, caching, rate limiting, and audit. It is built on the official MCP Go SDK, so the wire protocol (streamable HTTP, both request/response and SSE) is the SDK's own implementation on both the client-facing and upstream-facing sides.

Conformant, provably. The official @modelcontextprotocol/conformance suite runs against fold fronting the reference everything-server on every merge — 40/40 checks, including sampling, elicitation, logging, progress, and resource subscriptions bridged through the gateway (conformance job in CI; reproduce with ./scripts/conformance.sh).

Use cases

• Unify a federation. Acquisitions, child orgs, and teams each ship their own MCP servers; fold presents them as one virtual server with namespaced tools — no team rewrites anything.
• Draw the security boundary. One choke point for authentication, deny-by-default tool allowlists, per-principal visibility, and an audit event for every request including denials.
• Broker credentials. Clients hold one token with the gateway as audience; the gateway exchanges it per upstream (RFC 8693) or injects service credentials — API keys never reach agents.
• Protect fragile services. Caching, global and per-upstream rate limits, and circuit breakers stand between agent traffic storms and your internal systems.
• Govern vendor MCP servers. Put third-party/SaaS MCP endpoints behind your own auth, policy, and audit instead of scattering per-user API keys.

Quick start

cat > fold.config.json <<'EOF'
{
  "upstreams": [
    { "id": "github", "url": "https://mcp.example.com/mcp", "namespace": "github" }
  ]
}
EOF

go run github.com/fold-run/fold/cmd/fold@latest --config fold.config.json --port 8080
# MCP endpoint: http://localhost:8080/mcp
# Binds 127.0.0.1 by default; pass --host 0.0.0.0 to expose beyond loopback.

Or run the container (~22 MB, distroless):

docker run --rm -p 8080:8080 \
  -e FOLD_CONFIG="$(cat fold.config.json)" \
  ghcr.io/fold-run/fold:latest

FOLD_CONFIG accepts either a file path or the JSON document itself (convenient for container env injection). Prebuilt binaries for linux/darwin (amd64/arm64) are on the releases page, or go install github.com/fold-run/fold/cmd/fold@latest.

A single upstream without a namespace runs in passthrough mode (no name rewriting). Multiple upstreams require namespaces; tools and prompts are exposed as {namespace}__{name}.

Embedding in your own Go service is one call:

gw, err := gateway.New(cfg)   // cfg is a *config.Config
if err != nil { ... }
defer gw.Close()
http.ListenAndServe(":8080", gw.Handler())

A federated multi-org config — each upstream owned by a different team, in any language: