gcf-proxy

Bidirectional MCP proxy that translates between GCF and JSON. Drop-in, zero code changes to your server or client.

53-71% fewer input tokens. 63% fewer output tokens. 100% comprehension on every frontier model and 3 providers. 1,700+ LLM evaluations. Zero training.

Docs: gcformat.com · Proxy Guide · Playground · GCF vs TOON

Install

npm install -g @blackwell-systems/gcf-proxy

Setup (one line change)

Before:

{"mcpServers": {"yours": {"command": "your-mcp-server"}}}

After:

{"mcpServers": {"yours": {"command": "gcf-proxy", "args": ["your-mcp-server"]}}}

Works with Claude Code, Claude Desktop, VS Code, Cursor, and any MCP client.

What it does

Translates in both directions:

Responses:  Your Server (JSON) -> gcf-proxy encodes -> LLM reads GCF   (79% input savings)
Requests:   LLM writes GCF    -> gcf-proxy decodes -> Your Server (JSON) (63% output savings)

• Responses: JSON tool results from the server are encoded as GCF
• Requests: GCF strings in tool call arguments are decoded to JSON (4-byte prefix check, zero overhead)
• Non-convertible content passes through unchanged in both directions
• Neither the server nor the client needs to know about GCF

Benchmarks

| Format | Accuracy | Tokens | vs JSON | |--------|----------|--------|---------| | GCF | 90.7% avg (10 models) | 11,090 | 79% fewer | | TOON | 68.5% avg | 16,378 | 69% fewer | | JSON | 53.6% avg | 53,341 | baseline |

Also available on

• PyPI: pip install gcf-proxy
• Go: go install github.com/blackwell-systems/gcf-proxy@latest

Links

• Full Setup Guide
• GCF Specification
• GCF vs TOON
• GitHub