MCP Proxy — Upstream Server Proxying

PII Anonymizer connects to external MCP servers and proxies their tools. Arguments are anonymized before proxying.

Connecting an External Server

# config/settings.yaml
proxy:
  upstream_servers:
    github:
      transport: stdio
      command: docker
      args: ["run", "-i", "--rm", "-e", "GITHUB_PERSONAL_ACCESS_TOKEN", "ghcr.io/github/github-mcp-server"]
      env:
        GITHUB_PERSONAL_ACCESS_TOKEN: ""  # will be populated from environment
      enabled: true

Empty values in env are automatically populated from the process environment variables (convenient for .env in docker-compose).

Selective Anonymization

By default, all string values are anonymized. You can configure this specifically:

proxy:
  upstream_servers:
    searxng:
      transport: stdio
      command: docker
      args: ["run", "-i", "--rm", "-e", "SEARXNG_URL", "isokoliuk/mcp-searxng:latest"]
      env:
        SEARXNG_URL: "http://searxng:8080"
      enabled: true
      anonymize_fields:
        searxng_web_search: ["query"]   # anonymize only the query
        web_url_read: []                 # [] = do not anonymize

anonymize_fields Rules

Value	Behavior
Not specified	Anonymize all strings (backward compatibility)
[]	Disable anonymization for the tool
["query", "body"]	Anonymize only the specified fields

Example: GitHub

proxy:
  upstream_servers:
    github:
      transport: stdio
      command: docker
      args: ["run", "-i", "--rm", "-e", "GITHUB_PERSONAL_ACCESS_TOKEN", "ghcr.io/github/github-mcp-server"]
      env:
        GITHUB_PERSONAL_ACCESS_TOKEN: ""
      enabled: true
      anonymize_fields:
        create_issue: ["body", "title"]
        create_pull_request: ["body", "title"]
        search_code: []                 # do not anonymize the search query