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SwiftBlocksUI is a way to write interactive Slack messages and modal dialogs (also known as Slack "applications") using a SwiftUI like declarative style.

A blog article containing SwiftBlocksUI tutorials: Instant “SwiftUI” Flavoured Slack Apps.

This is what a full application looks like:

#!/usr/bin/swift sh
import SwiftBlocksUI // @SwiftBlocksUI


struct ClipItView: Blocks {

  @State(\.messageText) var messageText
  @State var importance = "medium"
  var body: some Blocks {
    View("Save it to ClipIt!") {
      TextEditor("Message Text", text: $messageText)
      Picker("Importance", selection: $importance) {
        "High 💎💎✨".tag("high")
        "Medium 💎"  .tag("medium")
        "Low ⚪️"     .tag("low")
      Submit("CliptIt") {
        console.log("Clip:", messageText, importance)

struct ClipIt: App {

  var body: some Endpoints {
    Use(logger("dev"), bodyParser.urlencoded(),
        sslCheck(verifyToken(allowUnsetInDebug: true)))
    MessageAction("clipit") {

try ClipIt.main()


There is a related blog entry going over SwiftBlocksUI: Instant “SwiftUI” Flavoured Slack Apps.

Additional documentation is going to arrive within this repository: Documentation.


  • SlashCows - Slack slash command that produces ASCII Cows. Moo!
  • AvocadoToast - An Avocado Toast ordering solution.
  • ClipIt! - Working on Messages.

Environment Variables

  • SLACK_ACCESS_TOKEN (the token required to send requests to Slack)
  • SLACK_VERIFICATION_TOKEN (shared secret with Slack to verify requests)
  • PORT (the port the app is going to start on, defaults to 1337)
  • LOG_SLACK_CLIENT_POSTS (set to 1 to log the JSON sent to Slack using SlackClient)
  • blocks.log.blocks (yes to log the structure of outgoing API blocks)
  • blocks.log.blocks.json (yes to log the raw JSON of outgoing blocks)
  • macro.core.numthreads
  • macro.core.iothreads
  • macro.core.retain.debug
  • macro.concat.maxsize
  • macro.streams.debug.rc
  • macro.router.debug
  • macro.router.matcher.debug


On Linux this currently requires a Swift 5.3 environment (swiftc crash, might be SR-12543).

On macOS it should work with Swift 5.2 (aka Xcode 11) and up, though 5.3 has some additional conveniences.



SwiftBlocksUI is brought to you by the Always Right Institute and ZeeZide. We like feedback, GitHub stars, cool contract work, presumably any form of praise you can think of.


Stars: 24


Statically Blocking - 2021-01-03T22:33:57

This version ties SwiftBlocksUI to Swift 5.3. Earlier Linux compilers are just crashing around on SwiftBlocksUI even though no 5.3 features are actually required. Swift 5.3.1 seems to be good on either platform.

Other additions:

  • add lots of Slack metadata to Logger's
  • uses new typed Macro request environment keys