Fetch backend

A JavaScript backend implemented using the Fetch API and backed via Future.

To use, add the following dependency to your project:

"com.softwaremill.sttp" %%% "core" % "1.5.11"

And add an implicit value:

implicit val sttpBackend = FetchBackend()

Timeouts are handled via the new AbortController class. As this class only recently appeared in browsers you may need to add a polyfill.

As browsers do not allow access to redirect responses, if a request sets followRedirects to false then a redirect will cause the response to return an error.

Note that Fetch does not pass cookies by default. If your request needs cookies then you will need to pass a FetchOptions instance with credentials set to either RequestCredentials.same-origin or RequestCredentials.include depending on your requirements.


Streaming support is provided via FetchMonixBackend. Note that streaming support on Firefox is hidden behind a flag, see ReadableStream for more information.

To use, add the following dependency to your project:

"com.softwaremill.sttp" %%% "monix" % "1.5.11"

An example of streaming a response:

import com.softwaremill.sttp._
import com.softwaremill.sttp.impl.monix._

import java.nio.ByteBuffer
import monix.eval.Task
import monix.reactive.Observable

implicit val sttpBackend = FetchMonixBackend()

val response: Task[Response[Observable[ByteBuffer]]] =


Currently no browsers support passing a stream as the request body. As such, using the Fetch backend with a streaming request will result in it being converted into an in-memory array before being sent. Response bodies are returned as a “proper” stream.