diff --git a/exercise/static/exercise/chapter.js b/exercise/static/exercise/chapter.js
index 659102fc6..d6b64810a 100644
--- a/exercise/static/exercise/chapter.js
+++ b/exercise/static/exercise/chapter.js
@@ -453,14 +453,16 @@
     },
 
     // Submit the formData to given url and then execute the callback.
-    submitAjax: function(url, formData, callback) {
+    submitAjax: function(url, formData, ajaxParams, callback) {
+      ajaxParams = ajaxParams ?? {};
+      ajaxParams.dataType = ajaxParams.dataType ?? "html";
       var exercise = this;
       $.ajax(url, {
         type: "POST",
         data: formData,
         contentType: false,
         processData: false,
-        dataType: "html"
+        ...ajaxParams,
       }).fail(function(xhr, textStatus, errorThrown) {
         //$(form_element).find(":input").prop("disabled", false);
         //exercise.showLoader("error");
@@ -596,24 +598,24 @@
           out_content.html("<p>Evaluating</p>");
 
           var url = exercise.url;
-          exercise.submitAjax(url, formData, function(data) {
-            const content = $(data);
-            // Look for error alerts in the feedback, but skip the hidden element
-            // that is always included: <div class="quiz-submit-error alert alert-danger hide">
+          exercise.submitAjax(url, formData, {dataType: "json"}, function(data) {
+            output.find(data.messages.selector).replaceWith(data.messages.html);
+
+            // Look for error alerts in the feedback
+            const content = $(data.page.content);
             const alerts = content.find('.alert-danger:not(.hide)');
-            if (!alerts.length) {
-              var poll_url = content.find(".exercise-wait").attr("data-poll-url");
-              output.attr('data-poll-url', poll_url);
-
-              exercise.updateSubmission(content);
-            } else if (alerts.contents().text()
-            .indexOf("The grading queue is not configured.") >= 0) {
-              output.find(exercise.settings.ae_result_selector)
-              .html(content.find(".alert:not(.hide)").text());
-              output.find(exercise.settings.ae_result_selector).append(content.find(".grading-task").text());
+            output.find(data.messages.selector).append(alerts);
+
+            if (data.submission) {
+              output.attr('data-poll-url', data.submission.poll_url);
+              output.attr('data-ready-url', data.submission.ready_url);
+
+              exercise.updateSubmission();
             } else {
-              output.find(exercise.settings.ae_result_selector)
-              .html(alerts.contents());
+              out_content.html("<p>Failed to submit:</p>")
+              for(const err of data.errors) {
+                out_content.append("<p>" + err + "</p>")
+              }
             }
           });
         });
@@ -636,7 +638,7 @@
           } else {
             formData.set('__aplus__', JSON.stringify({hash: hash}));
           }
-          exercise.submitAjax(url, formData, function(data) {
+          exercise.submitAjax(url, formData, {}, function(data) {
             //$(form_element).find(":input").prop("disabled", false);
             //exercise.hideLoader();
             var input = $(data);
diff --git a/exercise/views.py b/exercise/views.py
index ad95a6875..cb18ccce4 100644
--- a/exercise/views.py
+++ b/exercise/views.py
@@ -16,6 +16,8 @@
 from course.models import CourseModule
 from course.viewbase import CourseInstanceBaseView, EnrollableViewMixin
 from lib.helpers import query_dict_to_list_of_tuples, safe_file_name
+from lib.json import json_response_with_messages
+from lib.mime_request import accepts_mimes, MIMERequest
 from lib.remote_page import RemotePageNotFound, request_for_response
 from lib.viewbase import BaseRedirectMixin, BaseView
 from userprofile.models import UserProfile
@@ -141,7 +143,8 @@ def get(self, request: HttpRequest, *args: Any, **kwargs: Any) -> HttpResponse:
                            latest_enrollment_submission_data=all_enroll_data,
                            **kwargs)
 
-    def post(self, request: HttpRequest, *args: Any, **kwargs: Any) -> HttpResponse:
+    @accepts_mimes(["text/html", "application/json"])
+    def post(self, request: MIMERequest, *args: Any, **kwargs: Any) -> HttpResponse:
         # Stop submit trials for e.g. chapters.
         # However, allow posts from exercises switched to maintenance status.
         if not self.exercise.is_submittable:
@@ -149,7 +152,7 @@ def post(self, request: HttpRequest, *args: Any, **kwargs: Any) -> HttpResponse:
 
         new_submission = None
         page = ExercisePage(self.exercise)
-        _submission_status, submission_allowed, _issues, students = (
+        _submission_status, submission_allowed, issues, students = (
             self.submission_check(True, request)
         )
         if submission_allowed:
@@ -212,7 +215,17 @@ def post(self, request: HttpRequest, *args: Any, **kwargs: Any) -> HttpResponse:
 
             # Redirect non AJAX content page request back.
             if not request.is_ajax() and "__r" in request.GET:
-                return self.redirect(request.GET["__r"], backup=self.exercise);
+                return self.redirect(request.GET["__r"], backup=self.exercise)
+
+        if request.expected_mime == "application/json":
+            return json_response_with_messages(
+                request,
+                {
+                    "page": page,
+                    "submission": new_submission,
+                    "errors": issues,
+                }
+            )
 
         self.get_summary_submissions()
         return self.render_to_response(self.get_context_data(
diff --git a/lib/json.py b/lib/json.py
new file mode 100644
index 000000000..fc4d8f48c
--- /dev/null
+++ b/lib/json.py
@@ -0,0 +1,48 @@
+from typing import Any, Type
+from json import JSONEncoder
+
+from django.core.serializers.json import DjangoJSONEncoder
+from django.http import HttpRequest, JsonResponse
+from django.shortcuts import render
+
+from exercise.models import ExercisePage, Submission
+
+
+class AJAXJSONEncoder(DjangoJSONEncoder):
+    """Custom JSON encoder to implement encoding of our own types.
+
+    The purpose is different from the API serializers: this is meant for
+    returning specialized data about the object that is used in the site
+    javascript, instead of just serializing the object.
+    """
+    def default(self, obj: Any) -> Any:
+        if isinstance(obj, Submission):
+            return {
+                "id": obj.id,
+                "poll_url": obj.get_url("submission-poll"),
+                "ready_url": obj.get_url(
+                    getattr(self, "submission_poll_ready_url_name", "submission")
+                ),
+            }
+        elif isinstance(obj, ExercisePage):
+            return {
+                "content": obj.content,
+                "errors": obj.errors,
+            }
+
+        return super().default(obj)
+
+
+def json_response_with_messages(
+        request: HttpRequest,
+        data: dict,
+        encoder: Type[JSONEncoder] = AJAXJSONEncoder,
+        *args,
+        **kwargs,
+        ) -> JsonResponse:
+    data["messages"] = {
+        "selector": ".site-messages",
+        "html": render(request, "_messages.html").content.decode(),
+    }
+
+    return JsonResponse(data, encoder, *args, **kwargs)
diff --git a/lib/mime_request.py b/lib/mime_request.py
new file mode 100644
index 000000000..4af767267
--- /dev/null
+++ b/lib/mime_request.py
@@ -0,0 +1,107 @@
+from __future__ import annotations
+import functools
+from typing import Any, cast, List, Optional, Type
+
+from django.http import HttpRequest
+
+_mime_request_classes = {}
+def _mime_request_class(request: HttpRequest) -> Type[MIMERequest]:
+    """Return a MIMERequest class with the request's class as a parent class"""
+    if request.__class__ not in _mime_request_classes:
+        class _MIMERequest(MIMERequest, request.__class__):
+            ...
+
+        _mime_request_classes[request.__class__] = _MIMERequest
+
+    return _mime_request_classes[request.__class__]
+
+
+class MIMERequest(HttpRequest):
+    """Django HttpRequest but with <expected_mime> field. See accepts_mimes(...)"""
+    expected_mime: str
+
+    def __init__(self):
+        raise NotImplementedError("__init__() is not implemented. Use cast() instead.")
+
+    @staticmethod
+    def cast(request: HttpRequest, acceptable_mimes: List[str]) -> MIMERequest:
+        """Cast the given request to a MIMERequest, and return it.
+
+        Note that this changes the type of given original request to MIMERequest.
+        """
+        # Some trickery to add expected_mime to the request and change the type
+        # _mime_request_class is required because the request class is different
+        # depending on the situation. E.g. WSGIRequest vs HttpRequest
+        request.__class__ = _mime_request_class(request)
+        request = cast(MIMERequest, request)
+        request.expected_mime = accepted_mime(acceptable_mimes, request.headers.get("Accept"))
+        return request
+
+
+def accepts_mimes(acceptable: List[str]):
+    """Function/method decorator that changes the request object type to MIMERequest.
+
+    :param acceptable: list of acceptable mime types
+
+    The request object will have a <expected_mime> attribute with the mime type
+    that the client expects the response to be in. See accepted_mime(...) for
+    how the mime type is chosen.
+    """
+    # We need a class so that the decorator can be applied to both functions and methods
+    class SignatureChooser(object):
+        def __init__(self, func):
+            self.func = func
+            functools.wraps(func)(self)
+        def __call__(self, request, *args, **kwargs):
+            """Normal function call. This is called if self.func is a function"""
+            return self.call_with_mime(None, request, *args, **kwargs)
+        def __get__(self, instance: Optional[Any], _):
+            """Return class instance method. This is called if self.func is a method"""
+            return functools.partial(self.call_with_mime, instance)
+        def call_with_mime(self, obj: Optional[Any], request: HttpRequest, *args, **kwargs):
+            request = MIMERequest.cast(request, acceptable)
+            if obj is None:
+                return self.func(request, *args, **kwargs)
+            else:
+                return self.func(obj, request, *args, **kwargs)
+
+    return SignatureChooser
+
+
+def accepted_mime(acceptable: List[str], accept_header: Optional[str]):
+    """Return which mime type in <acceptable> matches <accept_header> first.
+
+    Match priority order is the following:
+    1. Exact match over a wild card match
+    2. Earlier types in <acceptable> are prioritized
+
+    Defaults to the first item in <acceptable> if no match was found.
+
+    For example,
+        accepted_mime(["text/html", "application/json"], "text/*, application/json")
+    and
+        accepted_mime(["text/html", "application/json"], "application/*")
+    will return "application/json" but
+        accepted_mime(["text/html", "application/json"], "text/html, application/json")
+    and
+        accepted_mime(["text/html", "application/json"], "text/*, application/*")
+    will return "text/html".
+    """
+    if accept_header is None or len(acceptable) == 1:
+        return acceptable[0]
+
+    accepts = [mime.split(";")[0].strip() for mime in accept_header.split(",")]
+
+    # Check for exact match first
+    for mime in acceptable:
+        if mime in accepts:
+            return mime
+
+    # Check for wildcard match
+    for mime in acceptable:
+        mime.split("/")
+        if f"{mime[0]}/*" in accepts or f"*/{mime[1]}" in accepts:
+            return mime
+
+    # Default to first element
+    return acceptable[0]
diff --git a/templates/_messages.html b/templates/_messages.html
index d50532173..2f02a0d03 100644
--- a/templates/_messages.html
+++ b/templates/_messages.html
@@ -1,8 +1,10 @@
 {% if messages %}
-    {% for message in messages %}
-        <div class="alert alert-{% if message.level == 10 %}success{% elif message.level == 40 %}danger{% else %}{{ message.tags }}{% endif %} clearfix site-message" role="alert">
-            <span class="glyphicon glyphicon-{% if message.level == 25 %}check{% else %}warning-sign{% endif %}" aria-hidden="true"></span>
-            <div class="message">{{ message|safe }}</div>
-        </div>
-    {% endfor %}
+    <div class="site-messages">
+        {% for message in messages %}
+            <div class="alert alert-{% if message.level == 10 %}success{% elif message.level == 40 %}danger{% else %}{{ message.tags }}{% endif %} clearfix site-message" role="alert">
+                <span class="glyphicon glyphicon-{% if message.level == 25 %}check{% else %}warning-sign{% endif %}" aria-hidden="true"></span>
+                <div class="message">{{ message|safe }}</div>
+            </div>
+        {% endfor %}
+    </div>
 {% endif %}