FieldFlow

FieldFlow turns OpenAPI-described REST endpoints into selectively filtered tools. It generates Pydantic models and FastAPI routes that forward requests to the upstream API and return only the fields the caller asks for. An optional MCP layer exposes the same functionality to Model Context Protocol clients such as Claude Desktop.

Features

• Discovers endpoints and schemas from OpenAPI 3.0 JSON or YAML files.
• Builds request/response Pydantic models dynamically, preserving aliases and optional fields.
• Generates FastAPI routes that accept parameters plus an optional fields list to slice responses.
• Proxies requests with httpx, automatically formatting URL paths and query parameters.
• Works with any OpenAPI-compliant spec, including nested schemas and refs.

Project Layout

fieldflow/
  config.py          # Environment-based settings
  http_app.py        # FastAPI app factory
  openapi_loader.py  # JSON/YAML loader with PyYAML fallback
  proxy.py           # Async HTTP proxy that filters responses to requested fields
  spec_parser.py     # Schema parser and dynamic Pydantic model generator
  tooling.py         # FastAPI router builder for tool endpoints
fieldflow_mcp/
  server.py          # MCP server wrapper built on FastMCP
  cli.py             # CLI entry point for the MCP server
examples/
  jsonplaceholder_openapi.yaml  # Minimal sample spec
  pokeapi_openapi.yaml          # Larger spec for stress-testing

Quickstart

python -m venv .venv
source .venv/bin/activate
pip install --upgrade pip
pip install -e '.[mcp]'  # zsh users: quote to avoid globbing
# Alternatively: pip install -r requirements.txt
fieldflow serve-http --reload