Inside Workflow DevKit: How framework integrations work
By Steven Van ·
WDK now supports eight frameworks, up from two at launch, including SvelteKit, Astro, Express and Hono.
Vercel's Workflow Development Kit (WDK) now works with eight frameworks, up from the two it launched with in October. WDK started out supporting Next.js and Nitro; it has since added SvelteKit, Astro, Express, and Hono, with TanStack Start and React Router integrations in active development. Vercel's latest post explains the pattern behind those integrations.
Every integration follows the same two-phase pattern regardless of framework. A build-time phase compiles workflow and step functions into handler files, bundles them, and sets up hot module replacement so changes appear without restarting the dev server. A runtime phase then exposes those handlers as HTTP endpoints, a process that differs by framework but always makes workflows reachable without manual endpoint configuration.
The compiling itself is done by WDK's SWC compiler plugin, which transforms the same source file into three different outputs depending on mode:
- Client mode runs via a Rollup or Vite plugin and turns workflow calls into HTTP client code.
- Step mode runs via esbuild and turns "use step" functions into server-side HTTP handlers.
- Workflow mode also runs via esbuild and turns "use workflow" functions into orchestrators that run in a sandboxed virtual environment.
