diff --git a/alembic/versions/3836d6b8e3f6_failed_submissions_and_next_grading_.py b/alembic/versions/3836d6b8e3f6_failed_submissions_and_next_grading_.py
new file mode 100644
index 0000000..8035045
--- /dev/null
+++ b/alembic/versions/3836d6b8e3f6_failed_submissions_and_next_grading_.py
@@ -0,0 +1,31 @@
+"""failed_submissions and next_grading_allowed_at columns added to grading_job table
+
+Revision ID: 3836d6b8e3f6
+Revises: 4baf7c606f77
+Create Date: 2025-11-09 13:03:28.701620
+
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = '3836d6b8e3f6'
+down_revision: Union[str, Sequence[str], None] = '4baf7c606f77'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.add_column('exercise_progress', sa.Column('skipped', sa.BOOLEAN(), nullable=False))
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_column('exercise_progress', 'skipped')
+    # ### end Alembic commands ###
diff --git a/app/api/v1/grading_job.py b/app/api/v1/grading_job.py
index 00cc80a..1ae63be 100644
--- a/app/api/v1/grading_job.py
+++ b/app/api/v1/grading_job.py
@@ -3,6 +3,7 @@
 from datetime import datetime
 from uuid import uuid4
 
+import sqlalchemy as sa
 from aio_pika import Message
 from aio_pika.abc import AbstractRobustChannel
 from fastapi import APIRouter, Depends, HTTPException
@@ -18,6 +19,8 @@
 from app.mq.message_queue import get_mq_channel
 from app.util import get_datetime_now
 
+INITIAL_JOB_STATUS = "pending"
+
 router = APIRouter(
     prefix="/grading-jobs",
     tags=["grading jobs"],
@@ -30,10 +33,12 @@ async def submit_grading_job(job_msg: dict, session: AsyncSession, ch: AbstractR
         id=job_msg["job_id"],
         tan_code=job_msg["tan_code"],
         exercise_id=job_msg["exercise_id"],
-        status="pending",
+        status=INITIAL_JOB_STATUS,
         started=now
     ))
 
+    await session.commit()
+
     job_msg["job_id"] = str(job_msg["job_id"])
 
     exchange = await ch.get_exchange(MQ_EXCHANGE_NAME)
@@ -53,6 +58,21 @@ async def create_submission(new_submission: ExerciseSubmission, session: AsyncSe
     if not exercise_progress:
         raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail="Tried to submit to an inactive exercise.")
 
+    if exercise_progress.next_grading_allowed_at and exercise_progress.next_grading_allowed_at > now:
+        raise HTTPException(status_code=status.HTTP_429_TOO_MANY_REQUESTS,
+                            detail=f"Next grading allowed at {exercise_progress.next_grading_allowed_at}")
+
+    stmt = select(GradingJob).where(sa.and_(GradingJob.exercise_id == new_submission.exercise_id,
+                                            GradingJob.tan_code == new_submission.tan_code,
+                                            GradingJob.status == INITIAL_JOB_STATUS))
+
+    result = await session.execute(stmt)
+    grading_job = result.scalars().first()
+
+    if grading_job:
+        raise HTTPException(status_code=status.HTTP_429_TOO_MANY_REQUESTS,
+                            detail="Previous grading job still in progress!")
+
     try:
         job_msg = {
             "job_id": uuid4(),
diff --git a/app/db/model/exercise.py b/app/db/model/exercise.py
index 7324bcd..d674eff 100644
--- a/app/db/model/exercise.py
+++ b/app/db/model/exercise.py
@@ -59,6 +59,8 @@ class ExerciseProgress(Base):
     start_time = sa.Column(sa.DateTime(timezone=True), nullable=False)
     end_time = sa.Column(sa.DateTime(timezone=True), nullable=True)
     skipped = sa.Column(sa.BOOLEAN, nullable=False)
+    failed_submissions = sa.Column(sa.INTEGER, nullable=False, default=0)
+    next_grading_allowed_at = sa.Column(sa.DateTime(timezone=True), nullable=True)
 
 
 class Competition(Base):
diff --git a/app/mq/message_queue.py b/app/mq/message_queue.py
index 81bcd04..2281a10 100644
--- a/app/mq/message_queue.py
+++ b/app/mq/message_queue.py
@@ -8,7 +8,7 @@
 
 async def get_mq_channel() -> AbstractRobustChannel:
     uri = f"amqp://{MQ_USER}:{MQ_PWD}@{MQ_URL}:{MQ_PORT}"
-    logging.debug('connect to: ', uri)
+    logging.debug(f'connect to:  {uri}')
     connection = await aio_pika.connect_robust(uri)
 
     async with connection:
diff --git a/tests/test_grading_job.py b/tests/test_grading_job.py
index cb2c675..f90a888 100644
--- a/tests/test_grading_job.py
+++ b/tests/test_grading_job.py
@@ -1,5 +1,5 @@
 import asyncio
-from datetime import timezone, datetime
+from datetime import datetime
 from unittest.mock import MagicMock, ANY, AsyncMock
 
 from aio_pika.abc import AbstractRobustChannel
@@ -39,7 +39,7 @@ async def get_mq_connection_override() -> AbstractRobustChannel:
 
         def get_datetime_now_override():
             def now():
-                yield datetime(2026, 10, 7, 19, 31, 0, tzinfo=timezone.utc)
+                yield datetime(2026, 10, 7, 19, 37, 0)
 
             return now
 
@@ -86,3 +86,65 @@ async def get_mq_connection_override() -> AbstractRobustChannel:
         assert response.status_code == status.HTTP_400_BAD_REQUEST
         channel_mock.get_exchange.assert_not_awaited()
         exchange_mock.publish.assert_not_awaited()
+
+    def test_early_grading_job_submission(self):
+        channel_mock, exchange_mock = setup_mocks()
+
+        async def get_mq_connection_override() -> AbstractRobustChannel:
+            yield channel_mock  # noqa
+
+        def get_datetime_now_override():
+            def now():
+                yield datetime(2025, 10, 7, 19, 31, 0)
+
+            return now
+
+        app.dependency_overrides[get_datetime_now] = get_datetime_now_override()
+        app.dependency_overrides[get_session] = get_override_dependency(self.engine)
+        app.dependency_overrides[get_mq_channel] = get_mq_connection_override
+
+        client = TestClient(app)
+
+        exercise_submission = {
+            "tan_code": "test-tan-1",
+            "exercise_id": 2,
+            "solution_code": "addi r0 r0 r0"
+        }
+
+        response = client.post("/grading-jobs", json=exercise_submission)
+
+        print(response.json())
+
+        assert response.status_code == status.HTTP_429_TOO_MANY_REQUESTS
+        assert response.json()["detail"] == "Next grading allowed at 2025-10-07 19:35:00"
+
+    def test_post_job_with_pending_job(self):
+        channel_mock, exchange_mock = setup_mocks()
+
+        async def get_mq_connection_override() -> AbstractRobustChannel:
+            yield channel_mock  # noqa
+
+        def get_datetime_now_override():
+            def now():
+                yield datetime(2025, 10, 7, 19, 50, 0)
+
+            return now
+
+        app.dependency_overrides[get_datetime_now] = get_datetime_now_override()
+        app.dependency_overrides[get_session] = get_override_dependency(self.engine)
+        app.dependency_overrides[get_mq_channel] = get_mq_connection_override
+
+        client = TestClient(app)
+
+        exercise_submission = {
+            "tan_code": "test-tan-4",
+            "exercise_id": 1,
+            "solution_code": "addi r0 r0 r0"
+        }
+
+        response = client.post("/grading-jobs", json=exercise_submission)
+
+        print(response.json())
+
+        assert response.status_code == status.HTTP_429_TOO_MANY_REQUESTS
+        assert response.json()["detail"] == "Previous grading job still in progress!"
diff --git a/tests/util/db_util.py b/tests/util/db_util.py
index cf10a03..64c1385 100644
--- a/tests/util/db_util.py
+++ b/tests/util/db_util.py
@@ -3,10 +3,10 @@
 from sqlalchemy.ext.asyncio import AsyncSession, AsyncEngine, async_sessionmaker
 
 from app.db.database import Base
-from app.db.model import Exercise, Tan, LoggingEvent
+from app.db.model import Exercise, Tan, LoggingEvent, GradingJob
 from app.db.model.exercise import ExerciseProgress, Competition, TestCase
 from tests.util.demo_data import COMPETITIONS, TANS, EXERCISES, EXERCISE_PROGRESS_ENTRIES, EXERCISE_TEST_CASES, \
-    LOGGING_EVENTS
+    LOGGING_EVENTS, GRADING_JOBS
 
 DB_URI = "sqlite+aiosqlite:///:memory:"
 
@@ -45,6 +45,9 @@ async def insert_demo_data(session_factory: async_sessionmaker):
             for test_case in EXERCISE_TEST_CASES[exercise_id]:
                 await insert_exercise_test_case(session, exercise_id, test_case)
 
+        for grading_job in GRADING_JOBS:
+            await insert_grading_job(session, grading_job)
+
 
 async def insert_exercise(session: AsyncSession, exercise: dict) -> None:
     exercise = Exercise(**exercise)
@@ -81,3 +84,9 @@ async def insert_exercise_test_case(session: AsyncSession, exercise_id: int, tes
     test_case = TestCase(exercise_id=exercise_id, **test_case)
     session.add(test_case)
     await session.commit()
+
+
+async def insert_grading_job(session: AsyncSession, grading_job: dict) -> None:
+    grading_job = GradingJob(**grading_job)
+    session.add(grading_job)
+    await session.commit()
diff --git a/tests/util/demo_data.py b/tests/util/demo_data.py
index ca730c7..dcd7623 100644
--- a/tests/util/demo_data.py
+++ b/tests/util/demo_data.py
@@ -1,4 +1,5 @@
 from datetime import datetime, timezone
+from uuid import uuid4
 
 COMPETITIONS = [
     {
@@ -24,6 +25,10 @@
         "competition_id": 1,
         "valid_from": datetime(2025, 10, 7, 18, 0, 0, tzinfo=timezone.utc),
     },
+    {
+        "code": "test-tan-4",
+        "competition_id": 1,
+    },
     {
         "code": "logging-test-tan",
         "competition_id": 1,
@@ -94,7 +99,8 @@
         "exercise_id": 2,
         "start_time": datetime(2025, 10, 7, 19, 30, 0, tzinfo=timezone.utc),
         "end_time": None,
-        "skipped": False
+        "skipped": False,
+        "next_grading_allowed_at": datetime(2025, 10, 7, 19, 35, 0, tzinfo=timezone.utc)
     },
     {
         "id": 3,
@@ -112,6 +118,25 @@
         "end_time": datetime(2025, 10, 7, 20, 0, 0, tzinfo=timezone.utc),
         "skipped": False
     },
+    {
+        "id": 5,
+        "tan_code": "test-tan-4",
+        "exercise_id": 1,
+        "start_time": datetime(2025, 10, 7, 19, 0, 0, tzinfo=timezone.utc),
+        "end_time": None,
+        "skipped": False
+    },
+
+]
+
+GRADING_JOBS = [
+    {
+        "id": uuid4(),
+        "tan_code": "test-tan-4",
+        "exercise_id": 1,
+        "status": "pending",
+        "started": datetime(2025, 10, 7, 18, 0, 0, tzinfo=timezone.utc),
+    }
 ]
 
 EXERCISE_TEST_CASES = {