Runtime boundaries

Datastar Kit is intentionally narrow. It speaks Datastar from ordinary fetch-compatible handlers and leaves application policy to your app.

const signals = await read.signals(request)
const input = FormSchema.parse(signals)

await todos.create({ ownerId: user.id, title: input.title })

return reply.done()

The handler is still yours. Datastar Kit only handles the Datastar-specific parts around it.

What the SDK owns

Use Datastar Kit for:

Area	API
Datastar attributes and actions	Native data-* TSX attributes, post(...), js, state(...)
Server HTML	TSX, renderToString, unsafeHtml
Signal request decoding	read.signals(request)
Datastar responses	reply.page(...), reply.patch(...), reply.signals(...), reply.stream(...), reply.done(...)
Stream chunks	event.patch(...), event.signals(...), event.navigate(...), event.script(...), event.comment(...)
Low-level protocol tests	datastar-kit/sse

The public APIs stay close to Web Standards: Request, Response, Headers, URL, ReadableStream, and plain objects.

What your app owns

Keep these concerns outside the SDK:

• routing and middleware;
• auth, sessions, CSRF, ownership checks, and rate limits;
• databases, caches, queues, brokers, and subscriptions;
• validation schemas and domain error mapping;
• request-local context;
• logging, tracing, metrics, and deployment lifecycle.

That boundary is what lets the same SDK work in Hono, Elysia, Bun, Deno, Cloudflare Workers, Node adapters, and custom fetch routers.

Request input

Use read.signals(request) when a Datastar action sends JSON signal state:

const state = await read.signals(request)
const input = SearchSchema.parse(state)

Use platform APIs for everything else:

const url = new URL(request.url)
const form = await request.formData()
const json = await request.json()

Datastar signals, HTML forms, query params, JSON APIs, and multipart uploads are different request inputs. Choose the reader that matches the route.

Response output

Use reply.* when the browser should receive Datastar-aware responses:

return reply.page(<TodosPage todos={todos} />)
return reply.patch(<TodoList todos={todos} />)
return reply.signals({ saved: true })
return reply.stream(events, { heartbeat: { intervalMs: 15_000 } })
return reply.navigate("/dashboard")
return reply.done()

Use plain Response objects for ordinary HTTP routes and non-Datastar clients.

Next: HTML and JSX.