@mcp-rating/gateway

Run MCP servers without handing them the API keys in your environment.

Whether a server you add can read your environment (AWS_SECRET_ACCESS_KEY, OPENAI_API_KEY, DATABASE_URL) depends on how your client starts it. The official MCP SDKs pass a short allowlist by default: HOME, PATH, USER and a few more. A client or script that passes its whole environment, often just to forward the one token a server needs, hands over everything. We haven't yet measured which popular clients do which, so we don't name any. The gateway doesn't leave it to the client: it spawns every server with a constructed environment, the SDK's short allowlist (PATH, HOME, USER and a few more) plus only the variables you or its manifest name. Nothing else from your environment is there to read.

Files are a different matter. By default a server still runs as you, so it can read what you can — ~/.ssh, ~/.aws/credentials, a project's .env. Only container isolation (opt-in, needs Docker) closes that. See what each level protects.

	Started with the whole environment	Through the gateway
Environment visible to the server	everything the client had	a short allowlist (PATH, HOME, USER and a few more), and what you name
Credentials in environment variables	all of them	none you didn't name
Credential files (~/.ssh, ~/.aws, .env)	readable	still readable, unless container isolation is on

Reproduce it yourself in about ten seconds: node demo/run-demo.mjs plants two fake credentials and runs the server both ways. It prints the planted values in full and, for anything real it finds in your environment, only the variable's name, never its value. The GIF is generated by node demo/render-gif.mjs from a clean, synthetic environment, so it shows nothing from any real machine.

It is also a meta-server: one entry in your config gives you the whole registry, connected on demand rather than pre-loaded.

{ "mcpServers": { "gateway": { "command": "npx", "args": ["-y", "@mcp-rating/gateway"] } } }

What it costs in context

Context used to be this README's lead argument: 13 meta-tools in place of every configured server's full schema. That assumed the client sends every tool definition on every request. Claude Code, Cursor and Kiro don't by default: they give the model your tools' names and load a definition when it's needed.

We measured all three in October 2026 with ten popular servers' real tool lists, replayed through a stub so that no third-party code ran. Added to every request, compared with no MCP servers:

	tools	Claude Code	Claude Code, tool search off	Cursor	Kiro (chars)
3 servers	45	+1,050	+14,143	+266	+3,974
9 servers	125	+3,085	+77,656	+910	+7,693
10 servers	500	+14,853	+183,889	+4,330	+26,398
the gateway	13	+716	+5,595	+342	+3,797

Claude Code 2.1.308 (tokens as the API counts them), Cursor 3.17.21 (its own estimate), Kiro 1.4.26 (characters, from its log). Compare within a column. Most of the ten-server cost is one server with 375 tools.

The gateway also takes more requests: it has to find and connect a server before calling it, and those steps stay in the conversation, so every later request sends them again. Over an eight-turn Claude Code session with default settings, the gateway used about 597,000 prompt tokens. Three servers configured directly used 475,000, nine used 510,000 and ten used 710,000. The gateway drew level with ten at the third or fourth turn, and never with three or nine.

So in these clients, don't use the gateway to save context. It still does when your client sends every definition upfront (Claude Code with tool search off), or against a server with hundreds of tools over a longer session. With a few typical servers, configuring them directly is cheaper.

The full write-up, with the method, the one-task bill and what we don't claim: MCP clients now load tool names, not schemas. Reproduce it with the scripts in demo/: claude-code-tokens.mjs (standing cost), claude-code-whole-bill.mjs (one task), claude-code-session.mjs (eight turns), cursor-standing.mjs and kiro-standing.mjs. Earlier versions of this section claimed 10× less context, then about 3×. Both came from our own harness, which sent every definition, like a client with tool search off.

How It Works

┌────────────────────┐       ┌──────────────┐       ┌──────────────────┐
│  Claude Desktop /  │ stdio │              │ stdio  │ MCP Server A     │
│  Cursor / Windsurf │◄─────►│  MCP Gateway │◄──────►│ (e.g. filesystem)│
│  (host client)     │       │              │◄──┐    └──────────────────┘
└────────────────────┘       └──────────────┘   │    ┌──────────────────┐
                                    │           └───►│ MCP Server B     │
                                    ▼                │ (e.g. github)    │
                             ┌──────────────┐        └──────────────────┘
                             │ MCP-Rating   │
                             │ Registry API │
                             └──────────────┘

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