Open Function Standard

The Open Function Standard (OFS) is a specification for writing portable backend functions. An OFS function declares its dependencies (database, cache, AI, etc.) in a manifest — the runtime provides them. The same function runs on Cloudflare Workers, Node.js, Bun, or Deno without modification.

The problem OFS solves

When you write a backend function today, it’s tightly coupled to your platform:

// Platform-specific: only works on Cloudflare Workers
export default {
  async fetch(request, env) {
    const db = env.DB
    const result = await db.prepare('SELECT * FROM users WHERE id = ?')
      .bind(userId)
      .first()
    return Response.json(result)
  }
}

Move this to Node.js or Bun? Rewrite everything.

The OFS approach

An OFS function declares what it needs. The runtime injects it:

// OFS function — runs on any supported runtime
export default async function getUser({ userId }, { sdk }) {
  const user = await sdk.db.queryOne('SELECT * FROM users WHERE id = ?', [userId])
  return { user }
}

The sdk argument is injected by the OFS runner. On Cloudflare Workers, it uses D1. On Node.js, it uses a compatible adapter. The function is identical.

OFS manifest

Every OFS function has an aerostack.json manifest:

{
  "name": "get-user",
  "version": "1.0.0",
  "description": "Fetch a user by ID",
  "runtime": "workers",
  "inputs": {
    "userId": { "type": "string", "required": true }
  },
  "outputs": {
    "user": { "type": "object" }
  },
  "requires": ["db"],
  "auth": "required"
}

Supported runtimes

Why this matters

• Publish once — share a function in the Community Hub that any project can use
• No vendor lock-in — your functions aren’t tied to one cloud
• Testable — run functions locally with mock SDK injections
• Composable — functions call other functions, building complex pipelines from simple pieces

Next steps

• Writing OFS Functions — step-by-step guide with examples
• Publishing to the Hub — share your functions with the community