Cloudflare Workers

Deploy Blazen to Cloudflare Workers, Deno Deploy, and other WASI edge runtimes

Overview

Blazen ships a wasm32-wasi build of the Node binding so the same blazen API works on Cloudflare Workers (workerd), Deno Deploy, Fastly Compute, and any other WASI-capable JS runtime. There are two install paths — pick the one that fits your dependency graph.

Two install paths

Both paths are zero-config — no Vite/Rollup plugins, no ssr.external lists, no manualChunks, no patch-package. Both work out of the box with wrangler ≥ 3.15 and @cloudflare/vite-plugin.

Path	Install	Import from	Notes
Alias (recommended)	`pnpm add @blazen-dev/wasi`	`@blazen-dev/wasi`	Single install. The alias lists the wasm sidecar as a regular dependency, so it’s pulled in transitively.
Subpath	`pnpm add blazen @blazen-dev/blazen-wasm32-wasi`	`blazen/workers`	Two installs. The wasm sidecar is an optional peer-dep on the umbrella `blazen` package, intentionally kept out of Node-only consumer installs.

The export surface is identical on both paths. Use the alias if you want a single pnpm add line for your Workers project. Use the subpath if you’d rather list blazen directly (mirroring a Node deployment) and explicitly pin the wasm sidecar.

Why the umbrella `blazen` package doesn’t auto-pull the wasm sidecar

Node servers receive a per-platform .node binary and never load the wasm shim. Forcing the wasm sidecar (a few MB compressed) into every Node consumer’s node_modules would tax installs and CI caches for no runtime benefit. The optional-peer-dep + alias-package split is what keeps both deployments tidy.

Quick start (alias path)

pnpm add @blazen-dev/wasi

// src/index.ts — a minimal Cloudflare Worker
import {
  CompletionModel,
  ChatMessage,
  AnthropicProvider,
  setDefaultHttpClient,
  HttpClient,
} from '@blazen-dev/wasi';

// Workerd has no `node:net` — register an HttpClient backed by global fetch
// at module load. (Same wiring as the subpath path.)
setDefaultHttpClient(
  HttpClient.fromCallback(async (req) => {
    const res = await fetch(req.url, {
      method: req.method,
      headers: req.headers,
      body: req.body,
    });
    const body = new Uint8Array(await res.arrayBuffer());
    return {
      status: res.status,
      headers: [...res.headers.entries()],
      body,
    };
  }),
);

export default {
  async fetch(req: Request, env: Env): Promise<Response> {
    const provider = await AnthropicProvider.create({ apiKey: env.ANTHROPIC_API_KEY });
    const model = CompletionModel.fromProvider(provider, 'claude-3-5-sonnet-latest');
    const result = await model.complete([ChatMessage.user('say hi')], {});
    return Response.json({ content: result.content });
  },
};

interface Env { ANTHROPIC_API_KEY: string; }

// wrangler.json
{
  "name": "my-blazen-worker",
  "main": "src/index.ts",
  "compatibility_date": "2026-05-13",
  "compatibility_flags": ["nodejs_compat"]
}

nodejs_compat is a standard Cloudflare flag (not Blazen-specific) needed for the napi-rs runtime helpers the wasm shim depends on.

Quick start (subpath path)

pnpm add blazen @blazen-dev/blazen-wasm32-wasi

import { CompletionModel, ChatMessage, AnthropicProvider } from 'blazen/workers';
// ... rest is identical to the alias path

The only difference is the import specifier. Under the hood both paths use the same blazen.workers.js loader, which uses wrangler’s static wasm import (import wasm from '@blazen-dev/blazen-wasm32-wasi/blazen.wasm32-wasi.wasm') — no import.meta.url, no fetch, no top-level new URL.

What you do NOT need

If you see any of these in a Workers project that imports Blazen, the fix has regressed — file a Blazen issue, do not work around it in your project:

No Vite resolveId plugin to externalize @blazen-dev/blazen-* subpackages.
No ssr.external / ssr.noExternal lists for blazen.
No optimizeDeps.exclude.
No manualChunks for Blazen.
No patch-package patches.
No @cloudflare/vinext-style auto-stubbing.

Working example

See examples/astro-cloudflare/ in the repo for an Astro 6 + @astrojs/cloudflare smoke test that exercises the subpath path end-to-end. The example’s README documents what it deliberately does NOT include — that list is the contract.