diff --git a/packages/frontend/src/app-extensions/index.ts b/packages/frontend/src/app-extensions/index.ts
new file mode 100644
index 000000000..53942d2ab
--- /dev/null
+++ b/packages/frontend/src/app-extensions/index.ts
@@ -0,0 +1,19 @@
+import type { FrontEndAppExtension } from './types'
+
+// Nothing for now
+const APP_EXTENSIONS: Record<string, FrontEndAppExtension> = {}
+
+export function getExtension(
+  appKey?: string,
+  stepKey?: string,
+): FrontEndAppExtension | null {
+  if (!appKey || !stepKey) {
+    return null
+  }
+  return APP_EXTENSIONS[`${appKey}-${stepKey}`] ?? null
+}
+
+export type {
+  CheckStepButtonExtensionProps,
+  FrontEndAppExtension,
+} from './types'
diff --git a/packages/frontend/src/app-extensions/types.ts b/packages/frontend/src/app-extensions/types.ts
new file mode 100644
index 000000000..d783c3e5e
--- /dev/null
+++ b/packages/frontend/src/app-extensions/types.ts
@@ -0,0 +1,22 @@
+import type { IStep } from '@plumber/types'
+
+import type { ComponentType, ReactNode } from 'react'
+
+export interface CheckStepButtonExtensionProps {
+  step: IStep
+  /** The Check Step / Check Step Again button itself. */
+  children: ReactNode
+}
+
+export interface FrontEndAppExtension {
+  /**
+   * Wraps the Check Step / Check Step Again button.
+   *
+   * Mounted ONLY WHEN the button is enabled.
+   * TBD: Allow extending when button is disabled (for showing custom failure
+   *      tooltip etc)
+   **/
+  CheckStepButton?: ComponentType<CheckStepButtonExtensionProps>
+
+  // Room to grow: ResultPanelWrapper, SubstepWrapper, etc.
+}
diff --git a/packages/frontend/src/components/FlowStepTestController/CheckAgainButton.tsx b/packages/frontend/src/components/FlowStepTestController/CheckAgainButton.tsx
index 18e6f5d3d..081b22715 100644
--- a/packages/frontend/src/components/FlowStepTestController/CheckAgainButton.tsx
+++ b/packages/frontend/src/components/FlowStepTestController/CheckAgainButton.tsx
@@ -1,6 +1,6 @@
 import { IExecutionStepMetadata, IStep } from '@plumber/types'
 
-import { useCallback, useMemo } from 'react'
+import { forwardRef, useCallback, useMemo } from 'react'
 import { IconType } from 'react-icons'
 import { BiChevronDown } from 'react-icons/bi'
 import { PiRobot, PiUser } from 'react-icons/pi'
@@ -30,7 +30,10 @@ interface CheckAgainButtonProps {
   executionStepMetadata?: IExecutionStepMetadata
 }
 
-export function CheckAgainButton(props: CheckAgainButtonProps) {
+export const CheckAgainButton = forwardRef<
+  HTMLButtonElement,
+  CheckAgainButtonProps
+>((props, ref) => {
   const { isUnstyledInfobox, onClick, isLoading, isDisabled, step } = props
   const isFormSgTrigger =
     step.appKey === FORMSG_APP_KEY && step.key === FORMSG_TRIGGER_KEY
@@ -38,13 +41,14 @@ export function CheckAgainButton(props: CheckAgainButtonProps) {
     step.appKey === FORMSG_APP_KEY && step.key === MRF_ACTION_KEY
 
   if (isFormSgTrigger) {
-    return <FormSGCheckAgainButton {...props} />
+    return <FormSGCheckAgainButton ref={ref} {...props} />
   }
   if (isFormSgAction) {
-    return <FormSGCheckAgainButton {...props} />
+    return <FormSGCheckAgainButton ref={ref} {...props} />
   }
   return (
     <Button
+      ref={ref}
       variant={isUnstyledInfobox ? 'solid' : 'outline'}
       onClick={() => onClick()}
       isLoading={isLoading}
@@ -56,7 +60,7 @@ export function CheckAgainButton(props: CheckAgainButtonProps) {
       Check step again
     </Button>
   )
-}
+})
 
 /**
  * For UX reasons, we need to have a different button for FormSG.
@@ -104,7 +108,10 @@ function FormSGMenuItem({
   )
 }
 
-function FormSGCheckAgainButton(props: CheckAgainButtonProps) {
+const FormSGCheckAgainButton = forwardRef<
+  HTMLButtonElement,
+  CheckAgainButtonProps
+>((props, ref) => {
   const {
     isUnstyledInfobox: isTransparentInfobox,
     onClick,
@@ -155,6 +162,7 @@ function FormSGCheckAgainButton(props: CheckAgainButtonProps) {
       colorScheme={isTransparentInfobox ? 'primary' : 'black'}
     >
       <Button
+        ref={ref}
         onClick={onTestClick}
         isLoading={isLoading}
         gap={2}
@@ -190,4 +198,4 @@ function FormSGCheckAgainButton(props: CheckAgainButtonProps) {
       )}
     </ButtonGroup>
   )
-}
+})
diff --git a/packages/frontend/src/components/FlowStepTestController/index.tsx b/packages/frontend/src/components/FlowStepTestController/index.tsx
index ecacc3621..e872f8b60 100644
--- a/packages/frontend/src/components/FlowStepTestController/index.tsx
+++ b/packages/frontend/src/components/FlowStepTestController/index.tsx
@@ -1,6 +1,13 @@
 import { IBaseTrigger, IStep, ITriggerInstructions } from '@plumber/types'
 
-import { useContext, useEffect, useMemo, useRef, useState } from 'react'
+import {
+  forwardRef,
+  useContext,
+  useEffect,
+  useMemo,
+  useRef,
+  useState,
+} from 'react'
 import { useFormContext } from 'react-hook-form'
 import { BiChevronDown, BiChevronUp } from 'react-icons/bi'
 import {
@@ -20,6 +27,7 @@ import {
   Infobox,
 } from '@opengovsg/design-system-react'
 
+import { CheckStepButtonExtensionProps, getExtension } from '@/app-extensions'
 import { EditorContext } from '@/contexts/Editor'
 import { validateStepParams } from '@/helpers/validateStepParams'
 import { useStepMetadata } from '@/hooks/useStepMetadata'
@@ -63,25 +71,32 @@ type CheckStepTooltipProps = {
   children: React.ReactNode
 }
 
-const CheckStepTooltip = (props: CheckStepTooltipProps) => {
-  const { children, hasDeletedVars, isDisabled, isReadOnly } = props
-  return (
-    <Tooltip
-      label={
-        isReadOnly
-          ? 'Unpublish your pipe to check step'
-          : hasDeletedVars
-          ? 'Remove variables from deleted steps to check step'
-          : 'Complete required fields to check step'
-      }
-      aria-label="check step tooltip"
-      isDisabled={isDisabled}
-      hasArrow
-    >
-      {children}
-    </Tooltip>
-  )
-}
+const CheckStepTooltip = forwardRef<HTMLDivElement, CheckStepTooltipProps>(
+  (props, ref) => {
+    const { children, hasDeletedVars, isDisabled, isReadOnly } = props
+    return (
+      <Tooltip
+        ref={ref}
+        label={
+          isReadOnly
+            ? 'Unpublish your pipe to check step'
+            : hasDeletedVars
+            ? 'Remove variables from deleted steps to check step'
+            : 'Complete required fields to check step'
+        }
+        aria-label="check step tooltip"
+        isDisabled={isDisabled}
+        hasArrow
+      >
+        {children}
+      </Tooltip>
+    )
+  },
+)
+
+const NoOpCheckStepButtonExtension = ({
+  children,
+}: CheckStepButtonExtensionProps) => children
 
 export default function FlowStepTestController(
   props: FlowStepTestControllerProps,
@@ -248,6 +263,12 @@ export default function FlowStepTestController(
     return collapseDirection === 'up' ? <BiChevronUp /> : <BiChevronDown />
   }
 
+  const appExtension = getExtension(step.appKey, step.key)
+  const CheckStepButtonExtension =
+    shouldAllowCheckStep && appExtension?.CheckStepButton != null
+      ? appExtension.CheckStepButton
+      : NoOpCheckStepButtonExtension
+
   return (
     <>
       {isWebhookSubstep && (
@@ -337,14 +358,16 @@ export default function FlowStepTestController(
                       {!isDirty ? 'Saved' : 'Save without checking'}
                     </Button>
                   )}
-                  <CheckAgainButton
-                    isUnstyledInfobox={isStepUnchecked}
-                    onClick={handleSaveAndTest}
-                    isLoading={isTestExecuting}
-                    isDisabled={!isValid || readOnly}
-                    step={step}
-                    executionStepMetadata={currentTestExecutionStep?.metadata}
-                  />
+                  <CheckStepButtonExtension step={step}>
+                    <CheckAgainButton
+                      isUnstyledInfobox={isStepUnchecked}
+                      onClick={handleSaveAndTest}
+                      isLoading={isTestExecuting}
+                      isDisabled={!isValid || readOnly}
+                      step={step}
+                      executionStepMetadata={currentTestExecutionStep?.metadata}
+                    />
+                  </CheckStepButtonExtension>
                 </Flex>
               </Flex>
             </Infobox>
@@ -379,20 +402,22 @@ export default function FlowStepTestController(
                   {isDirty ? 'Save' : 'Saved'}
                 </Button>
               )}
-              <CheckStepTooltip
-                hasDeletedVars={hasDeletedVars}
-                isDisabled={shouldAllowCheckStep}
-                isReadOnly={readOnly}
-              >
-                <Button
-                  onClick={() => handleSaveAndTest()}
-                  data-test="flow-substep-continue-button"
-                  isDisabled={!shouldAllowCheckStep}
-                  isLoading={isTestExecuting}
+              <CheckStepButtonExtension step={step}>
+                <CheckStepTooltip
+                  hasDeletedVars={hasDeletedVars}
+                  isDisabled={shouldAllowCheckStep}
+                  isReadOnly={readOnly}
                 >
-                  Check step
-                </Button>
-              </CheckStepTooltip>
+                  <Button
+                    onClick={() => handleSaveAndTest()}
+                    data-test="flow-substep-continue-button"
+                    isDisabled={!shouldAllowCheckStep}
+                    isLoading={isTestExecuting}
+                  >
+                    Check step
+                  </Button>
+                </CheckStepTooltip>
+              </CheckStepButtonExtension>
             </HStack>
           </VStack>
         )}