diff --git a/src/server/devserver/dxt-devtool-baselayout.html b/src/server/devserver/dxt-devtool-baselayout.html
index ca39a0be8..9a814e1c7 100644
--- a/src/server/devserver/dxt-devtool-baselayout.html
+++ b/src/server/devserver/dxt-devtool-baselayout.html
@@ -1,4 +1,4 @@
-{% extends "govuk/template.njk" %}
+{% extends "index.html" %}
 
 {% from "govuk/components/back-link/macro.njk" import govukBackLink -%}
 {% from "govuk/components/footer/macro.njk" import govukFooter -%}
@@ -31,6 +31,10 @@
   }) }}
 {% endblock %}
 
+{% block buttons %}
+I've overridden the buttons
+{% endblock %}
+
 {% block header %}
   {{ govukHeader({
     homepageUrl: currentPath if context.isForceAccess else "https://defra.github.io/forms-engine-plugin/",
@@ -41,16 +45,6 @@
   }) }}
 {% endblock %}
 
-{% block beforeContent %}
-  {% if backLink %}
-    {{ govukBackLink(backLink) }}
-  {% endif %}
-{% endblock %}
-
-{% block content %}
-  <h1 class="govuk-heading-l">Default page template</h1>
-{% endblock %}
-
 {% block bodyEnd %}
   <script type="module" nonce="{{ cspNonce }}" src="{{ getDxtAssetPath("application.js") }}"></script>
 {% endblock %}
diff --git a/src/server/plugins/engine/configureEnginePlugin.ts b/src/server/plugins/engine/configureEnginePlugin.ts
index c003d48c2..acee81509 100644
--- a/src/server/plugins/engine/configureEnginePlugin.ts
+++ b/src/server/plugins/engine/configureEnginePlugin.ts
@@ -53,7 +53,10 @@ export const configureEnginePlugin = async ({
       cacheName: 'session',
       nunjucks: {
         baseLayoutPath: 'dxt-devtool-baselayout.html',
-        paths: [join(findPackageRoot(), 'src/server/devserver')] // custom layout to make it really clear this is not the same as the runner
+        paths: [
+          join(findPackageRoot(), 'src/server/devserver'), // custom layout to make it really clear this is not the same as the runner
+          join(findPackageRoot(), 'src/server/plugins/engine/views') // add engine views path so dxt-devtool-baselayout.html can find index.html
+        ]
       },
       viewContext: devtoolContext,
       preparePageEventRequestOptions,
@@ -61,6 +64,40 @@ export const configureEnginePlugin = async ({
       baseUrl: 'http://localhost:3009', // always runs locally
       saveAndReturn
     }
+
+    /*
+    To enable custom buttons, use this config:
+
+    ```
+      actionHandlers: {
+        'withdraw-submission': async (request, _) => {
+          await getCacheService(request.server).clearState(request)
+          return '/summary'
+        }
+      }
+    ```
+
+    /*
+    To enable save and return for testing purposes, use this config:
+
+    ```
+    saveAndReturn: {
+      keyGenerator: (_) => {
+        return `save-and-return`
+      },
+      sessionHydrator: (_) => {
+        return Promise.resolve({
+          applicantFirstName: 'Joe'
+        })
+      },
+      sessionPersister: () => {
+        console.log('no-op')
+      }
+    }
+    ```
+
+    Then load http://localhost:3009/page-events-demo and the applicantFirstName should be pre-filled as 'Joe'
+     */
   }
 }
 
diff --git a/src/server/plugins/engine/helpers.ts b/src/server/plugins/engine/helpers.ts
index 5feae0c8c..727ff2b86 100644
--- a/src/server/plugins/engine/helpers.ts
+++ b/src/server/plugins/engine/helpers.ts
@@ -12,7 +12,7 @@ import Boom from '@hapi/boom'
 import { type ResponseToolkit, type Server } from '@hapi/hapi'
 import { format, parseISO } from 'date-fns'
 import { StatusCodes } from 'http-status-codes'
-import { type Schema, type ValidationErrorItem } from 'joi'
+import Joi, { type Schema, type ValidationErrorItem } from 'joi'
 import { Liquid } from 'liquidjs'
 
 import { createLogger } from '~/src/server/common/helpers/logging/logger.js'
@@ -376,6 +376,18 @@ export function evaluateTemplate(
   })
 }
 
+export function getSchemas(server?: Server) {
+  if (!server) {
+    // only used in debug UI helper where validation isn't really important
+    return {
+      actionSchema: Joi.any().required(),
+      paramsSchema: Joi.any().required()
+    }
+  }
+
+  return getPluginOptions(server).schemas
+}
+
 export function getCacheService(server: Server) {
   return getPluginOptions(server).cacheService
 }
diff --git a/src/server/plugins/engine/options.js b/src/server/plugins/engine/options.js
index aec627846..03432b177 100644
--- a/src/server/plugins/engine/options.js
+++ b/src/server/plugins/engine/options.js
@@ -24,7 +24,8 @@ const pluginRegistrationOptionsSchema = Joi.object({
     keyGenerator: Joi.function(),
     sessionHydrator: Joi.function(),
     sessionPersister: Joi.function()
-  }).optional()
+  }).optional(),
+  actionHandlers: Joi.object().pattern(Joi.string(), Joi.function())
 })
 
 /**
diff --git a/src/server/plugins/engine/pageControllers/PageController.ts b/src/server/plugins/engine/pageControllers/PageController.ts
index d3c475998..b7d570c63 100644
--- a/src/server/plugins/engine/pageControllers/PageController.ts
+++ b/src/server/plugins/engine/pageControllers/PageController.ts
@@ -46,7 +46,7 @@ export class PageController {
   condition?: ExecutableCondition
   events?: Events
   collection?: ComponentCollection
-  viewName = 'index'
+  viewName = 'dxt-devtool-baselayout.html'
   allowSaveAndReturn = false
 
   constructor(model: FormModel, pageDef: Page) {
diff --git a/src/server/plugins/engine/pageControllers/QuestionPageController.ts b/src/server/plugins/engine/pageControllers/QuestionPageController.ts
index c43afb82f..c17de0ad0 100644
--- a/src/server/plugins/engine/pageControllers/QuestionPageController.ts
+++ b/src/server/plugins/engine/pageControllers/QuestionPageController.ts
@@ -8,9 +8,8 @@ import {
   type Link,
   type Page
 } from '@defra/forms-model'
-import Boom from '@hapi/boom'
 import { type ResponseToolkit, type RouteOptions } from '@hapi/hapi'
-import { type ValidationErrorItem } from 'joi'
+import Joi, { type ValidationErrorItem } from 'joi'
 
 import { ComponentCollection } from '~/src/server/plugins/engine/components/ComponentCollection.js'
 import { optionalText } from '~/src/server/plugins/engine/components/constants.js'
@@ -18,7 +17,7 @@ import { type BackLink } from '~/src/server/plugins/engine/components/types.js'
 import {
   getCacheService,
   getErrors,
-  getSaveAndReturnHelpers,
+  getSchemas,
   normalisePath,
   proceed
 } from '~/src/server/plugins/engine/helpers.js'
@@ -35,17 +34,12 @@ import {
   type FormSubmissionState
 } from '~/src/server/plugins/engine/types.js'
 import {
-  FormAction,
   type FormRequest,
   type FormRequestPayload,
   type FormRequestPayloadRefs,
   type FormRequestRefs
 } from '~/src/server/routes/types.js'
-import {
-  actionSchema,
-  crumbSchema,
-  paramsSchema
-} from '~/src/server/schemas/index.js'
+import { crumbSchema } from '~/src/server/schemas/index.js'
 import { merge } from '~/src/server/services/cacheService.js'
 
 export class QuestionPageController extends PageController {
@@ -64,7 +58,7 @@ export class QuestionPageController extends PageController {
 
     this.collection.formSchema = this.collection.formSchema.keys({
       crumb: crumbSchema,
-      action: actionSchema
+      action: Joi.string()
     })
   }
 
@@ -276,7 +270,7 @@ export class QuestionPageController extends PageController {
   getFormParams(request?: FormContextRequest): FormPayloadParams {
     const { payload } = request ?? {}
 
-    const result = paramsSchema.validate(payload, {
+    const result = getSchemas(request?.server).paramsSchema.validate(payload, {
       abortEarly: false,
       stripUnknown: true
     })
@@ -515,10 +509,13 @@ export class QuestionPageController extends PageController {
         return h.view(viewName, viewModel)
       }
 
-      // Check if this is a save-and-return action
+      // Check if this is a custom action that needs handling
       const { action } = request.payload
-      if (action === FormAction.SaveAndReturn) {
-        return this.handleSaveAndReturn(request, context, h)
+      const { actionHandlers } = request.server.plugins['forms-engine-plugin']
+
+      if (action && action in actionHandlers) {
+        const exitPath = await actionHandlers[action](request, context)
+        return h.redirect(this.getHref(exitPath))
       }
 
       // Save and proceed
@@ -539,31 +536,6 @@ export class QuestionPageController extends PageController {
     return proceed(request, h, nextUrl)
   }
 
-  /**
-   * Handle save-and-return action by processing form data and redirecting to exit page
-   */
-  async handleSaveAndReturn(
-    request: FormRequestPayload,
-    context: FormContext,
-    h: Pick<ResponseToolkit, 'redirect' | 'view'>
-  ) {
-    const { state } = context
-
-    // Save the current state and redirect to exit page
-    const saveAndReturn = getSaveAndReturnHelpers(request.server)
-
-    if (!saveAndReturn?.sessionPersister) {
-      throw Boom.internal('Server misconfigured for save and return')
-    }
-
-    await saveAndReturn.sessionPersister(state, request)
-
-    const cacheService = getCacheService(request.server)
-    await cacheService.clearState(request)
-
-    return h.redirect(this.getHref('/exit'))
-  }
-
   /**
    * {@link https://hapi.dev/api/?v=20.1.2#route-options}
    */
diff --git a/src/server/plugins/engine/pageControllers/buttonHandlers.ts b/src/server/plugins/engine/pageControllers/buttonHandlers.ts
new file mode 100644
index 000000000..ab2e1e069
--- /dev/null
+++ b/src/server/plugins/engine/pageControllers/buttonHandlers.ts
@@ -0,0 +1,32 @@
+import Boom from '@hapi/boom'
+
+import {
+  getCacheService,
+  getSaveAndReturnHelpers
+} from '~/src/server/plugins/engine/helpers.js'
+import { type FormContext } from '~/src/server/plugins/engine/types.js'
+import { type FormRequestPayload } from '~/src/server/routes/types.js'
+
+/**
+ * Handle save-and-return action by processing form data and return exit path
+ */
+export async function handleSaveAndReturn(
+  request: FormRequestPayload,
+  context: FormContext
+): Promise<string> {
+  const { state } = context
+
+  // Save the current state and return the exit path
+  const saveAndReturn = getSaveAndReturnHelpers(request.server)
+
+  if (!saveAndReturn?.sessionPersister) {
+    throw Boom.internal('Server misconfigured for save and return')
+  }
+
+  await saveAndReturn.sessionPersister(state, request)
+
+  const cacheService = getCacheService(request.server)
+  await cacheService.clearState(request)
+
+  return '/exit'
+}
diff --git a/src/server/plugins/engine/plugin.ts b/src/server/plugins/engine/plugin.ts
index f915614c4..728e6c2a7 100644
--- a/src/server/plugins/engine/plugin.ts
+++ b/src/server/plugins/engine/plugin.ts
@@ -8,6 +8,7 @@ import {
 
 import { type FormModel } from '~/src/server/plugins/engine/models/index.js'
 import { validatePluginOptions } from '~/src/server/plugins/engine/options.js'
+import { handleSaveAndReturn } from '~/src/server/plugins/engine/pageControllers/buttonHandlers.js'
 import { getRoutes as getSaveAndReturnExitRoutes } from '~/src/server/plugins/engine/routes/exit.js'
 import { getRoutes as getFileUploadStatusRoutes } from '~/src/server/plugins/engine/routes/file-upload.js'
 import { makeLoadFormPreHandler } from '~/src/server/plugins/engine/routes/index.js'
@@ -17,9 +18,14 @@ import { getRoutes as getRepeaterSummaryRoutes } from '~/src/server/plugins/engi
 import { type PluginOptions } from '~/src/server/plugins/engine/types.js'
 import { registerVision } from '~/src/server/plugins/engine/vision.js'
 import {
+  FormAction,
   type FormRequestPayloadRefs,
   type FormRequestRefs
 } from '~/src/server/routes/types.js'
+import {
+  buildActionSchema,
+  buildParamsSchema
+} from '~/src/server/schemas/index.js'
 import { CacheService } from '~/src/server/services/index.js'
 
 export const plugin = {
@@ -49,10 +55,18 @@ export const plugin = {
 
     await registerVision(server, options)
 
+    const actionHandlers = getActionHandlers(options)
+    const customActions = Object.keys(actionHandlers)
+
     server.expose('baseLayoutPath', nunjucksOptions.baseLayoutPath)
     server.expose('viewContext', viewContext)
     server.expose('cacheService', cacheService)
     server.expose('saveAndReturn', saveAndReturn)
+    server.expose('actionHandlers', actionHandlers)
+    server.expose('schemas', {
+      actionSchema: buildActionSchema(customActions),
+      paramsSchema: buildParamsSchema(customActions)
+    })
 
     server.app.model = model
 
@@ -86,12 +100,13 @@ export const plugin = {
 
     const routes = [
       ...getQuestionRoutes(
+        server,
         getRouteOptions,
         postRouteOptions,
         preparePageEventRequestOptions
       ),
-      ...getRepeaterSummaryRoutes(getRouteOptions, postRouteOptions),
-      ...getRepeaterItemDeleteRoutes(getRouteOptions, postRouteOptions),
+      ...getRepeaterSummaryRoutes(server, getRouteOptions, postRouteOptions),
+      ...getRepeaterItemDeleteRoutes(server, getRouteOptions, postRouteOptions),
       ...getSaveAndReturnExitRoutes(getRouteOptions),
       ...getFileUploadStatusRoutes()
     ]
@@ -99,3 +114,15 @@ export const plugin = {
     server.route(routes as unknown as ServerRoute[]) // TODO
   }
 } satisfies Plugin<PluginOptions>
+
+function getActionHandlers(pluginOptions: PluginOptions) {
+  let actionHandlers: PluginOptions['actionHandlers'] = {
+    [FormAction.SaveAndReturn]: handleSaveAndReturn
+  }
+
+  if (pluginOptions.actionHandlers) {
+    actionHandlers = pluginOptions.actionHandlers
+  }
+
+  return actionHandlers
+}
diff --git a/src/server/plugins/engine/routes/questions.ts b/src/server/plugins/engine/routes/questions.ts
index 049074f8a..4ebad8fe3 100644
--- a/src/server/plugins/engine/routes/questions.ts
+++ b/src/server/plugins/engine/routes/questions.ts
@@ -4,11 +4,13 @@ import {
   type ResponseObject,
   type ResponseToolkit,
   type RouteOptions,
+  type Server,
   type ServerRoute
 } from '@hapi/hapi'
 import Joi from 'joi'
 
 import {
+  getSchemas,
   normalisePath,
   proceed,
   redirectPath
@@ -35,7 +37,6 @@ import {
   type FormRequestRefs
 } from '~/src/server/routes/types.js'
 import {
-  actionSchema,
   crumbSchema,
   itemIdSchema,
   pathSchema,
@@ -164,10 +165,13 @@ function isSuccessful(response: ResponseObject): boolean {
 }
 
 export function getRoutes(
+  server: Server,
   getRouteOptions: RouteOptions<FormRequestRefs>,
   postRouteOptions: RouteOptions<FormRequestPayloadRefs>,
   preparePageEventRequestOptions?: PreparePageEventRequestOptions
 ): (ServerRoute<FormRequestRefs> | ServerRoute<FormRequestPayloadRefs>)[] {
+  const { actionSchema } = getSchemas(server)
+
   return [
     {
       method: 'get',
diff --git a/src/server/plugins/engine/routes/repeaters/item-delete.ts b/src/server/plugins/engine/routes/repeaters/item-delete.ts
index ad18c92ae..c8e962df4 100644
--- a/src/server/plugins/engine/routes/repeaters/item-delete.ts
+++ b/src/server/plugins/engine/routes/repeaters/item-delete.ts
@@ -3,10 +3,12 @@ import Boom from '@hapi/boom'
 import {
   type ResponseToolkit,
   type RouteOptions,
+  type Server,
   type ServerRoute
 } from '@hapi/hapi'
 import Joi from 'joi'
 
+import { getSchemas } from '~/src/server/plugins/engine/helpers.js'
 import { FileUploadPageController } from '~/src/server/plugins/engine/pageControllers/FileUploadPageController.js'
 import { RepeatPageController } from '~/src/server/plugins/engine/pageControllers/RepeatPageController.js'
 import { redirectOrMakeHandler } from '~/src/server/plugins/engine/routes/index.js'
@@ -17,7 +19,6 @@ import {
   type FormRequestRefs
 } from '~/src/server/routes/types.js'
 import {
-  actionSchema,
   confirmSchema,
   crumbSchema,
   itemIdSchema,
@@ -70,9 +71,12 @@ function postHandler(
 }
 
 export function getRoutes(
+  server: Server,
   getRouteOptions: RouteOptions<FormRequestRefs>,
   postRouteOptions: RouteOptions<FormRequestPayloadRefs>
 ): (ServerRoute<FormRequestRefs> | ServerRoute<FormRequestPayloadRefs>)[] {
+  const { actionSchema } = getSchemas(server)
+
   return [
     {
       method: 'get',
diff --git a/src/server/plugins/engine/routes/repeaters/summary.ts b/src/server/plugins/engine/routes/repeaters/summary.ts
index 557980dca..214208b6a 100644
--- a/src/server/plugins/engine/routes/repeaters/summary.ts
+++ b/src/server/plugins/engine/routes/repeaters/summary.ts
@@ -4,10 +4,12 @@ import Boom from '@hapi/boom'
 import {
   type ResponseToolkit,
   type RouteOptions,
+  type Server,
   type ServerRoute
 } from '@hapi/hapi'
 import Joi from 'joi'
 
+import { getSchemas } from '~/src/server/plugins/engine/helpers.js'
 import { RepeatPageController } from '~/src/server/plugins/engine/pageControllers/RepeatPageController.js'
 import { redirectOrMakeHandler } from '~/src/server/plugins/engine/routes/index.js'
 import {
@@ -17,7 +19,6 @@ import {
   type FormRequestRefs
 } from '~/src/server/routes/types.js'
 import {
-  actionSchema,
   crumbSchema,
   pathSchema,
   stateSchema
@@ -56,9 +57,12 @@ function postHandler(
 }
 
 export function getRoutes(
+  server: Server,
   getRouteOptions: RouteOptions<FormRequestRefs>,
   postRouteOptions: RouteOptions<FormRequestPayloadRefs>
 ): (ServerRoute<FormRequestRefs> | ServerRoute<FormRequestPayloadRefs>)[] {
+  const { actionSchema } = getSchemas(server)
+
   return [
     {
       method: 'get',
diff --git a/src/server/plugins/engine/types.ts b/src/server/plugins/engine/types.ts
index 3a566d6ff..106d055cf 100644
--- a/src/server/plugins/engine/types.ts
+++ b/src/server/plugins/engine/types.ts
@@ -383,4 +383,6 @@ export interface PluginOptions {
   preparePageEventRequestOptions?: PreparePageEventRequestOptions
   onRequest?: OnRequestCallback
   baseUrl: string // base URL of the application, protocol and hostname e.g. "https://myapp.com"
+  buttons?: PluginProperties['forms-engine-plugin']['buttons']
+  actionHandlers?: PluginProperties['forms-engine-plugin']['actionHandlers']
 }
diff --git a/src/server/plugins/engine/views/index.html b/src/server/plugins/engine/views/index.html
index af3258c88..3fa2cee0d 100644
--- a/src/server/plugins/engine/views/index.html
+++ b/src/server/plugins/engine/views/index.html
@@ -1,8 +1,15 @@
-{% extends baseLayoutPath %}
+{% extends "govuk/template.njk" %}
 
 {% from "govuk/components/error-summary/macro.njk" import govukErrorSummary %}
+{% from "govuk/components/button/macro.njk" import govukButton %}
 {% from "partials/components.html" import componentList with context %}
 
+{% block beforeContent %}
+  {% if backLink %}
+    {{ govukBackLink(backLink) }}
+  {% endif %}
+{% endblock %}
+
 {% block content %}
   <div class="govuk-grid-row">
     <div class="govuk-grid-column-two-thirds">
@@ -25,9 +32,37 @@
 
       {% block form %}
         {% if page.allowContinue %}
-          {% include "partials/form.html" %}
+          <form method="post" novalidate>
+            <input type="hidden" name="crumb" value="{{ crumb }}">
+
+            {% block formComponents %}
+              {{ componentList(components) }}
+            {% endblock %}
+
+            {% block formButtons %}
+              <div class="govuk-button-group">
+                {{ govukButton({
+                  text: "Start now" if isStartPage else "Continue",
+                  isStartButton: isStartPage,
+                  preventDoubleClick: true
+                }) }}
+
+                {% if allowSaveAndReturn %}
+                  {{ govukButton({
+                    text: "Save and return",
+                    classes: "govuk-button--secondary",
+                    name: "action",
+                    value: "save-and-return",
+                    preventDoubleClick: true
+                  }) }}
+                {% endif %}
+              </div>
+            {% endblock %}
+          </form>
         {% else %}
-          {{ componentList(components) }}
+          {% block nonFormComponents %}
+            {{ componentList(components) }}
+          {% endblock %}
         {% endif %}
       {% endblock %}
     </div>
diff --git a/src/server/plugins/engine/views/partials/form.html b/src/server/plugins/engine/views/partials/form.html
index fb3476725..36eedf704 100644
--- a/src/server/plugins/engine/views/partials/form.html
+++ b/src/server/plugins/engine/views/partials/form.html
@@ -4,23 +4,27 @@
 <form method="post" novalidate>
   <input type="hidden" name="crumb" value="{{ crumb }}">
 
-  {{ componentList(components) }}
+  {% block components %}
+    {{ componentList(components) }}
+  {% endblock %}
 
-  <div class="govuk-button-group">
-    {{ govukButton({
-      text: "Start now" if isStartPage else "Continue",
-      isStartButton: isStartPage,
-      preventDoubleClick: true
-    }) }}
-
-    {% if allowSaveAndReturn %}
+  {% block buttons %}
+    <div class="govuk-button-group">
       {{ govukButton({
-        text: "Save and return",
-        classes: "govuk-button--secondary",
-        name: "action",
-        value: "save-and-return",
+        text: "Start now" if isStartPage else "Continue",
+        isStartButton: isStartPage,
         preventDoubleClick: true
       }) }}
-    {% endif %}
-  </div>
+
+      {% if allowSaveAndReturn %}
+        {{ govukButton({
+          text: "Save and return",
+          classes: "govuk-button--secondary",
+          name: "action",
+          value: "save-and-return",
+          preventDoubleClick: true
+        }) }}
+      {% endif %}
+    </div>
+  {% endblock %}
 </form>
diff --git a/src/server/plugins/nunjucks/types.js b/src/server/plugins/nunjucks/types.js
index 2ad7ad3d7..530ea3b70 100644
--- a/src/server/plugins/nunjucks/types.js
+++ b/src/server/plugins/nunjucks/types.js
@@ -17,6 +17,7 @@
  * @property {string} [currentPath] - Current path
  * @property {string} [previewMode] - Preview mode
  * @property {string} [slug] - Form slug
+ * @property {object[]} [buttons] - Button override
  * @property {FormContext} [context] - the current form context
  */
 
diff --git a/src/server/schemas/index.ts b/src/server/schemas/index.ts
index 38006860c..4ff6824f3 100644
--- a/src/server/schemas/index.ts
+++ b/src/server/schemas/index.ts
@@ -7,7 +7,7 @@ export const stateSchema = Joi.string<FormStatus>()
   .valid(FormStatus.Draft, FormStatus.Live)
   .required()
 
-export const actionSchema = Joi.string<FormAction>()
+const actionSchema = Joi.string<FormAction>()
   .valid(
     FormAction.Continue,
     FormAction.Validate,
@@ -24,7 +24,7 @@ export const itemIdSchema = Joi.string().uuid().required()
 export const crumbSchema = Joi.string().optional().allow('')
 export const confirmSchema = Joi.boolean().empty(false)
 
-export const paramsSchema = Joi.object<FormPayloadParams>()
+const paramsSchema = Joi.object<FormPayloadParams>()
   .keys({
     action: actionSchema,
     confirm: confirmSchema,
@@ -33,3 +33,13 @@ export const paramsSchema = Joi.object<FormPayloadParams>()
   })
   .default({})
   .optional()
+
+export function buildActionSchema(customActions: string[]) {
+  return actionSchema.valid(...customActions)
+}
+
+export function buildParamsSchema(customActions: string[]) {
+  return paramsSchema.alter({
+    action: (schema) => schema.valid(...customActions)
+  })
+}
diff --git a/src/typings/hapi/index.d.ts b/src/typings/hapi/index.d.ts
index 8067b4e43..0852e8acb 100644
--- a/src/typings/hapi/index.d.ts
+++ b/src/typings/hapi/index.d.ts
@@ -2,11 +2,13 @@
 
 import { type Plugin } from '@hapi/hapi'
 import { type ServerYar, type Yar } from '@hapi/yar'
+import { type Schema as JoiSchema } from 'joi'
 import { type Logger } from 'pino'
 
 import { type FormModel } from '~/src/server/plugins/engine/models/index.js'
 import { type PluginOptions } from '~/src/server/plugins/engine/types.ts'
 import {
+  type FormAction,
   type FormRequest,
   type FormRequestPayload
 } from '~/src/server/routes/types.js'
@@ -26,6 +28,19 @@ declare module '@hapi/hapi' {
         request: FormRequest | FormRequestPayload | null
       ) => Record<string, unknown> | Promise<Record<string, unknown>>
       saveAndReturn?: PluginOptions['saveAndReturn']
+      buttons?: {
+        text: string
+        name?: string
+        action?: string
+      }[]
+      actionHandlers: Record<
+        FormAction | string,
+        (request: FormRequestPayload, context: FormContext) => Promise<string>
+      >
+      schemas: {
+        actionSchema: JoiSchema
+        paramsSchema: JoiSchema
+      }
     }
   }