FFI Design

SkillMedia

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

Instructions available. Your AI can read the instructions. Execution depends on the setup they require.

Account requirements not reviewed. Check the skill instructions before use; ahel provides instructions and does not run this skill.

Add ahel to your AI once: Claude, ChatGPT, Cursor, Claude Code or Codex. Then ask it to use this.

Then ask your AI: use the FFI Design skill

What this skill tells your AI

The instructions your AI receives, as published by a5c-ai/babysitter in library/specializations/programming-languages/skills/ffi-design/SKILL.md and read by ahel’s review.

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" }
    }
  }
}

Signals

GitHub stars: 2k
Forks: 112
Last commit: Sep 2026

Advanced

Item type: skill
Key: ffi-design
Source: github.com/a5c-ai/babysitter

github.com/a5c-ai/babysitter