Plantime and Runtime

Alchemy programs operate in two distinct phases: plantime and runtime. Understanding this split is key to working with platform resources like Workers and Lambda Functions.

The two phases

Phase	When it runs	What it does
Plantime (Init)	During alchemy deploy / plan	Declares resources, resolves bindings, computes the plan
Runtime (Exec)	When handling a request	Executes your application logic

Init and Exec in code

Platform resources express this split with the “Effect returning an Effect” pattern:

Cloudflare.Worker(
  "Worker",
  { main: import.meta.path },
  Effect.gen(function* () {
    // ─── Init phase (plantime + runtime) ───
    const bucket = yield* Cloudflare.R2Bucket.bind(Bucket);

    return {
      // ─── Exec phase (runtime only) ───
      fetch: Effect.gen(function* () {
        const obj = yield* bucket.get("key");
        return HttpServerResponse.text(yield* obj.text());
      }),
    };
  }),
);

Init phase code runs in both plantime and runtime:

• At plantime, it registers bindings and resolves dependencies
• At runtime, it initializes SDK clients and prepares the handler

Exec phase code runs only at runtime, when an actual request arrives.

ALCHEMY_PHASE

The current phase is exposed as the ALCHEMY_PHASE environment variable / config:

Value	Context
plan	Default. Running alchemy deploy or alchemy plan.
dev	Running alchemy dev (local development with hot reload).
runtime	Running inside a deployed Worker or Lambda Function.

This is used internally by Alchemy — for example, Binding.Policy enforces that policy providers are registered at plantime but gracefully becomes a no-op at runtime (where the policy layer is not provided).

Why this matters

The init/exec split means you can write code that:

1. Resolves infrastructure references at deploy time — bindings know which bucket ARN, queue URL, etc. to inject
2. Initializes SDK clients once at cold start — not on every request
3. Handles requests with a pre-configured context — the bucket variable in exec already knows which bucket to talk to

Effect.gen(function* () {
  // Init: runs once at cold start
  const bucket = yield* Cloudflare.R2Bucket.bind(Bucket);
  const kv = yield* Cloudflare.KVNamespace.bind(KV);

  return {
    // Exec: runs per request
    fetch: Effect.gen(function* () {
      // bucket and kv are already initialized
      const obj = yield* bucket.get("key");
      // ...
    }),
  };
});