gcf-proxy — MCP server for Claude Code: shrunken tool output
A proxy that sits between an MCP client and server, re-encoding tool responses as GCF to cut token use. One line in your config.
claude mcp add gcf-proxy -- npx -y @blackwell-systems/gcf-proxyWhat gcf-proxy does
gcf-proxy wraps any MCP server and rewrites what comes back. Structured JSON from a tool gets re-encoded as GCF; GCF that shows up inside tool call arguments gets decoded to JSON before forwarding. Nothing on either side has to change.
Two ways to run it. Locally over stdio, where gcf-proxy is the command and your server goes in the args. For a remote server, point --upstream at a Streamable HTTP endpoint. The --http :9090 flag turns the proxy itself into an HTTP service with a /health check.
Three flags do the heavy lifting: --session for dedup of symbols already sent, --cache for repeated identical calls, --delta for responses that shift a little. Responses under 100 bytes are left alone. On open-weight models, --no-flatten keeps nested objects expanded, since that form reads better there.
What it helps with
- shrink the JSON an MCP server dumps into context
- add compression to a third-party server you cannot edit
- proxy a remote MCP server over HTTP
- watch per-call token savings in stderr logs
- keep nested objects readable for models that struggle with flat encoding
Example prompts for the agent
- Wrap the memory MCP server with gcf-proxy and show me the savings
- Run
gcf-proxy --verbose uvx yfinance-mcpand report how many tokens were saved - Connect gcf-proxy to a remote server with
--upstream http://host:3000/mcp
How to install gcf-proxy
Platform CLI
claude mcp add gcf-proxy -- npx -y @blackwell-systems/gcf-proxyPlatform CLI
codex mcp add gcf-proxy -- npx -y @blackwell-systems/gcf-proxyConfig file
{
"mcpServers": {
"gcf-proxy": {
"command": "npx",
"args": [
"-y",
"@blackwell-systems/gcf-proxy"
]
}
}
}Config file
{
"servers": {
"gcf-proxy": {
"type": "stdio",
"command": "npx",
"args": [
"-y",
"@blackwell-systems/gcf-proxy"
]
}
}
}Platform CLI
gemini mcp add gcf-proxy npx -y @blackwell-systems/gcf-proxyStep by step, with commands for each platform: How to add an MCP server to Claude Code, Codex, Cursor, VS Code, Gemini CLI and more
Questions about gcf-proxy
How do I install gcf-proxy in Claude Code?
One command: claude mcp add gcf-proxy -- npx -y @blackwell-systems/gcf-proxy.
What does gcf-proxy do?
It converts MCP tool responses from JSON into GCF and decodes GCF found in tool call arguments back to JSON. Neither the client nor the server needs editing.
Do I need to modify the MCP server?
No. The proxy spawns the server as a subprocess and talks over stdin/stdout. If you own the server, the authors suggest using the GCF libraries directly for finer control over session dedup and delta encoding.
