refract-mcp 0.4.0

MCP proxy that compresses tool schemas — up to -98% tokens, 100% signal preserved

Refract

Cuts up to 97% of the tokens your AI agents spend using MCP tools — without losing anything.

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The problem in one sentence

When your AI agent (Claude, Cursor...) connects to an external tool — your calendar, your emails, GitHub — it downloads the full description of every available tool, every single time, even if it only ends up using one.

It's like asking someone to read the entire store catalogue just to buy bread.

Refract fixes that. It sits between your agent and the tool server, and only lets through what's actually needed.

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What it actually changes

	Without Refract	With Refract
Filesystem tools (14 tools)	1,892 tokens	236 tokens (−88%)
Google Calendar tools (5 tools)	5,010 tokens	660 tokens (−87%)
Enterprise pack — Calendar + Gmail + Drive (12 tools)	8,649 tokens	882 tokens (−90%)
sample_app.js (JavaScript)	799 tok	284 tok (−64.5%)
sample_app.ts (TypeScript)	378 tok	266 tok (−29.6%)

Fewer tokens sent = lower API bills, faster responses.

And nothing is lost. Every check confirmed tools stay 100% usable after compression and no required information is ever stripped.

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Install

pip install refract-mcp

That's it. No API key required, no account needed.

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How to use it

With Claude Desktop

Open your Claude Desktop config file and add:

{
  "mcpServers": {
    "my-tool-via-refract": {
      "command": "refract-proxy",
      "args": [
        "--target",
        "npx @modelcontextprotocol/server-filesystem /path/to/folder",
        "--verbose"
      ]
    }
  }
}

Replace the --target line with any MCP server you already use. Restart Claude Desktop and that's it, Refract runs in the background.

You may have this message when launching Claude Desktop :"Failed to spawn process: No such file or directory" in Claude Desktop

This usually means Claude Desktop can't find refract-proxy in its PATH. Find the absolute path and use it directly in your config:

which refract-proxy

Then use the full path in claude_desktop_config.json:

{
  "mcpServers": {
    "my-tool-via-refract": {
      "command": "/full/path/to/refract-proxy",
      "args": [
        "--target",
        "npx @modelcontextprotocol/server-filesystem /path/to/folder",
        "--verbose"
      ]
    }
  }
}

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From the command line

refract-proxy --target "npx @modelcontextprotocol/server-filesystem /tmp" --verbose

The --verbose flag shows live savings:

[Refract] Connected to npx @modelcontextprotocol/server-filesystem /tmp
  14 tools  |  1892 → 236 tokens  (88% reduction)

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How it works, no jargon

Refract optimizes information retrieval by sending an agent a simple index of tool names instead of a massive summary of all available data. Once the required tool is identified, the system delivers only the necessary full details and automatically verifies that no important content was lost during the compression. Operating completely without artificial intelligence, this streamlined process is entirely automated, fast, and predictable.

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Two modes

Mode 1 — MCP Proxy (compress external tool schemas)

Sits between your agent and any MCP server. Compresses tool schemas on the fly so your agent doesn't load the full catalogue on every request.

refract-proxy --target "npx @modelcontextprotocol/server-filesystem /tmp" --verbose

Mode 2 — MCP Server (analyse your own Python code)

Exposes your codebase as an MCP server. Your agent can index a repo, get compressed file context, or expand specific functions with their full source and dependencies.

refract-server --root /path/to/your/repo

Add it to Claude Desktop:

{
  "mcpServers": {
    "refract-code": {
      "command": "/path/to/refract-server",
      "args": ["--root", "/path/to/your/repo"]
    }
  }
}

Then ask Claude directly:

• "Index the repo and tell me which file has the most functions"
• "Get the compressed version of src/auth.py and show token reduction"
• "Expand the function authenticate and show its dependencies"

Tool	Input	Output
index_repo	repo path	aggregated index of all Python files
get_compressed	file path	compressed structure + token stats
expand	file path + function names	verbatim source + dependency context

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Works with

• Claude Desktop
• Cursor
• Any client that follows the MCP (Model Context Protocol) standard
• Any existing MCP server — your internal tools, GitHub, Google Workspace, Slack, etc.
• Python, Javascript, typescript, JSX, TSX

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For developers

Python usage

from refract_proxy import RefractProxy

proxy = RefractProxy(
    target_url="npx @modelcontextprotocol/server-filesystem /tmp",
    verbose=True,
)
await proxy.connect()

# Use compressed tools directly with the Anthropic API
tools = proxy.as_anthropic_tools(use_cache=True)

# Or serve as a local MCP server (stdio)
await proxy.serve()

# Or expose it via HTTP/SSE
await proxy.serve_http()  # → http://localhost:8080/sse

HTTP/SSE mode

refract-proxy --target "https://my-mcp-server.com" --mode http --port 8080

With a local schema file (for testing)

refract-proxy --target schemas/mcp_calendar_schemas.json --verbose

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Built-in Anthropic caching

Refract integrates with Anthropic prompt caching: as_anthropic_tools() automatically marks the compressed catalogue as cacheable, cutting costs even further on repeated requests.

Example over 30 days, 100 requests/day, 5,000 tokens of schemas:

	Cost
Without Refract, without cache	$45.00
With Refract + cache	$1.49

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License

MIT — free to use, including commercially. ENDOFREADME