Babysitter FFI Design

Expert skill for designing and implementing foreign function interfaces to native code

install

source · Clone the upstream repo

git clone https://github.com/a5c-ai/babysitter

Claude Code · Install into ~/.claude/skills/

T=$(mktemp -d) && git clone --depth=1 https://github.com/a5c-ai/babysitter "$T" && mkdir -p ~/.claude/skills && cp -r "$T/library/specializations/programming-languages/skills/ffi-design" ~/.claude/skills/a5c-ai-babysitter-ffi-design && rm -rf "$T"

manifest: library/specializations/programming-languages/skills/ffi-design/SKILL.md

FFI Design Skill

Overview

Expert skill for designing and implementing foreign function interfaces to native code.

Capabilities

Design FFI declaration syntax
Implement type marshaling between languages
Handle C calling conventions (cdecl, stdcall, fastcall)
Implement callback support (native calling managed)
Handle string encoding conversions
Implement struct layout matching (padding, alignment)
Design memory ownership transfer rules
Support dynamic library loading

Target Processes

ffi-implementation.js
interpreter-implementation.js
bytecode-vm-implementation.js
code-generation-llvm.js

Dependencies

libffi
Platform ABI documentation

Usage Guidelines

Safety: Design safe wrappers around unsafe FFI calls
Marshaling: Document type marshaling rules explicitly
Ownership: Make memory ownership clear at FFI boundaries
Callbacks: Handle callback lifetimes carefully
Strings: Handle string encoding conversions correctly (UTF-8, UTF-16)

Output Schema

{
  "type": "object",
  "properties": {
    "callingConventions": {
      "type": "array",
      "items": { "type": "string" }
    },
    "marshalingRules": {
      "type": "array",
      "items": {
        "type": "object",
        "properties": {
          "sourceType": { "type": "string" },
          "targetType": { "type": "string" }
        }
      }
    },
    "callbackSupport": { "type": "boolean" },
    "generatedFiles": {
      "type": "array",
      "items": { "type": "string" }
    }
  }
}