Bun Ffi

Lets you call C and C++ libraries directly from Bun using the bun:ffi module. You get dlopen for loading shared libraries, FFI type definitions for mapping JavaScript to native types, and helpers for working with pointers and strings. The skill covers function definitions, struct handling, callbacks, and memory management. Most useful when you need to integrate existing native libraries without writing Node.js addons or when performance matters enough to justify the pointer juggling. The SQLite example is solid if you want to see a real use case. Just remember FFI calls are synchronous and block the main thread, so move heavy work to Web Workers.

skills.sh installs: 326
GitHub stars: 248
last updated: Aug 21, 2026

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Install

$ npx -y skills add secondsky/claude-skills --skill bun-ffi --agent claude-code

Installs into .claude/skills of the current project.

Files

Bun FFI

Bun's FFI allows calling native C/C++ libraries from JavaScript.

Quick Start

import { dlopen, suffix, FFIType } from "bun:ffi";

// Load library
const lib = dlopen(`libc.${suffix}`, {
  printf: {
    args: [FFIType.cstring],
    returns: FFIType.int,
  },
});

// Call function
lib.symbols.printf("Hello from C!\n");

Loading Libraries

Platform-Specific Paths

import { dlopen, suffix } from "bun:ffi";

// suffix is: "dylib" (macOS), "so" (Linux), "dll" (Windows)

// System library
const libc = dlopen(`libc.${suffix}`, { ... });

// Custom library
const myLib = dlopen(`./libmylib.${suffix}`, { ... });

// Absolute path
const sqlite = dlopen("/usr/lib/libsqlite3.so", { ... });

Cross-Platform Loading

function getLibPath(name: string): string {
  const platform = process.platform;
  const paths = {
    darwin: `/usr/local/lib/lib${name}.dylib`,
    linux: `/usr/lib/lib${name}.so`,
    win32: `C:\\Windows\\System32\\${name}.dll`,
  };
  return paths[platform] || paths.linux;
}

const lib = dlopen(getLibPath("mylib"), { ... });