Configure MCP Filters with Explicit Type and Transport

Plano filters integrate with external services via MCP (Model Context Protocol) or plain HTTP. MCP filters call a specific tool on a remote MCP server. Always specify type, transport, and optionally tool (defaults to the filter id) to ensure Plano connects correctly to your filter implementation.

Incorrect (minimal filter definition relying on all defaults):

yaml

filters:
  - id: my_guard          # Plano infers type=mcp, transport=streamable-http, tool=my_guard
    url: http://localhost:10500
    # If your MCP server uses a different tool name or transport, this silently misroutes

Correct (explicit configuration for each filter):

yaml

version: v0.3.0

filters:
  - id: input_guards
    url: http://host.docker.internal:10500
    type: mcp                        # Explicitly MCP protocol
    transport: streamable-http       # Streamable HTTP transport
    tool: input_guards               # MCP tool name (matches MCP server registration)

  - id: query_rewriter
    url: http://host.docker.internal:10501
    type: mcp
    transport: streamable-http
    tool: rewrite_query              # Tool name differs from filter ID — explicit is safer

  - id: custom_validator
    url: http://host.docker.internal:10503
    type: http                       # Plain HTTP filter (not MCP)
    # No tool field for HTTP filters

MCP filter implementation contract: Your MCP server must expose a tool matching the tool name. The tool receives the request payload and must return either:

A modified request (to pass through with changes)
A rejection response (to short-circuit the pipeline)

HTTP filter alternative — use type: http for simpler request/response interceptors that don't need the MCP protocol:

yaml

filters:
  - id: auth_validator
    url: http://host.docker.internal:9000/validate
    type: http    # Plano POSTs the request, expects the modified request back

Reference: https://github.com/katanemo/archgw