diff --git a/CHANGELOG.md b/CHANGELOG.md
index 611790d2e..b99160c73 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+# Changed
+- Source validation happens before simulation upload and raises an error if no source is present.
+
 ## [2.3.0] - 2023-6-30
 
 ### Added
diff --git a/tests/test_web/test_webapi.py b/tests/test_web/test_webapi.py
index 026cbf969..36801e9c7 100644
--- a/tests/test_web/test_webapi.py
+++ b/tests/test_web/test_webapi.py
@@ -9,7 +9,7 @@
 
 from responses import matchers
 
-from tidy3d import Simulation
+from tidy3d.exceptions import SetupError
 from tidy3d.web.environment import Env
 from tidy3d.web.webapi import delete, delete_old, download, download_json, run
 from tidy3d.web.webapi import download_log, estimate_cost, get_info, get_run_info, get_tasks
@@ -32,7 +32,14 @@
 
 def make_sim():
     """Makes a simulation."""
-    return td.Simulation(size=(1, 1, 1), grid_spec=td.GridSpec.auto(wavelength=1.0), run_time=1e-12)
+    pulse = td.GaussianPulse(freq0=200e12, fwidth=20e12)
+    pt_dipole = td.PointDipole(source_time=pulse, polarization="Ex")
+    return td.Simulation(
+        size=(1, 1, 1),
+        grid_spec=td.GridSpec.auto(wavelength=1.0),
+        run_time=1e-12,
+        sources=[pt_dipole],
+    )
 
 
 @pytest.fixture
@@ -226,6 +233,14 @@ def mock_webapi(
     """Mocks all webapi operation."""
 
 
+@responses.activate
+def test_source_validation(mock_upload):
+    sim = make_sim().copy(update={"sources": []})
+    assert upload(sim, TASK_NAME, PROJECT_NAME, source_required=False)
+    with pytest.raises(SetupError):
+        upload(sim, TASK_NAME, PROJECT_NAME)
+
+
 @responses.activate
 def test_upload(mock_upload):
     sim = make_sim()
@@ -453,7 +468,7 @@ def test_main(mock_webapi, monkeypatch, mock_job_status):
     # batch_data = run_async(sims, folder_name=PROJECT_NAME)
 
     def save_sim_to_path(path: str) -> None:
-        sim = Simulation(size=(1, 1, 1), grid_spec=td.GridSpec.auto(wavelength=1.0), run_time=1e-12)
+        sim = make_sim()
         sim.to_file(path)
 
     monkeypatch.setattr("builtins.input", lambda _: "Y")
diff --git a/tidy3d/components/simulation.py b/tidy3d/components/simulation.py
index 3db87ea3b..c51ca9673 100644
--- a/tidy3d/components/simulation.py
+++ b/tidy3d/components/simulation.py
@@ -579,7 +579,7 @@ def _warn_monitor_simulation_frequency_range(cls, val, values):
 
         source_ranges = [source.source_time.frequency_range() for source in values["sources"]]
         if not source_ranges:
-            log.warning("No sources in simulation.")
+            log.info("No sources in simulation.")
             return val
 
         freq_min = min((freq_range[0] for freq_range in source_ranges), default=0.0)
@@ -890,14 +890,22 @@ def _validate_tfsf_nonuniform_grid(self) -> None:
 
     """ Pre submit validation (before web.upload()) """
 
-    def validate_pre_upload(self) -> None:
-        """Validate the fully initialized simulation is ok for upload to our servers."""
+    def validate_pre_upload(self, source_required: bool = True) -> None:
+        """Validate the fully initialized simulation is ok for upload to our servers.
+
+        Parameters
+        ----------
+        source_required: bool = True
+            If ``True``, validation will fail in case no sources are found in the simulation.
+        """
         self._validate_size()
         self._validate_monitor_size()
         self._validate_datasets_not_none()
         self._validate_tfsf_structure_intersections()
         # self._validate_run_time()
         _ = self.volumetric_structures
+        if source_required and len(self.sources) == 0:
+            raise SetupError("No sources in simulation.")
 
     def _validate_size(self) -> None:
         """Ensures the simulation is within size limits before simulation is uploaded."""
diff --git a/tidy3d/plugins/mode/web.py b/tidy3d/plugins/mode/web.py
index 8aadf7beb..16847a8f2 100644
--- a/tidy3d/plugins/mode/web.py
+++ b/tidy3d/plugins/mode/web.py
@@ -189,7 +189,7 @@ def create(
             mode_spec = mode_solver.mode_spec.copy(update={"precision": "single"})
             mode_solver = mode_solver.copy(update={"mode_spec": mode_spec})
 
-        mode_solver.simulation.validate_pre_upload()
+        mode_solver.simulation.validate_pre_upload(source_required=False)
         resp = http.post(
             MODESOLVER_API,
             {
diff --git a/tidy3d/web/webapi.py b/tidy3d/web/webapi.py
index df738fbf4..61c0f79d4 100644
--- a/tidy3d/web/webapi.py
+++ b/tidy3d/web/webapi.py
@@ -142,6 +142,7 @@ def upload(  # pylint:disable=too-many-locals,too-many-arguments
     progress_callback: Callable[[float], None] = None,
     simulation_type: str = "tidy3d",
     parent_tasks: List[str] = None,
+    source_required: bool = True,
 ) -> TaskId:
     """Upload simulation to server, but do not start running :class:`.Simulation`.
 
@@ -164,6 +165,8 @@ def upload(  # pylint:disable=too-many-locals,too-many-arguments
         Type of simulation being uploaded.
     parent_tasks : List[str]
         List of related task ids.
+    source_required: bool = True
+        If ``True``, simulations without sources will raise an error before being uploaded.
 
     Returns
     -------
@@ -175,7 +178,7 @@ def upload(  # pylint:disable=too-many-locals,too-many-arguments
     To start the simulation running, must call :meth:`start` after uploaded.
     """
 
-    simulation.validate_pre_upload()
+    simulation.validate_pre_upload(source_required=source_required)
     log.debug("Creating task.")
 
     task = SimulationTask.create(