diff --git a/buildbot_nix/__init__.py b/buildbot_nix/__init__.py
index d86f31b..ab16883 100644
--- a/buildbot_nix/__init__.py
+++ b/buildbot_nix/__init__.py
@@ -453,13 +453,21 @@ class NixEvalCommand(buildstep.ShellMixin, steps.BuildStep):
 
         return result
 
-def make_job_evaluator(name: str, settings: EvaluatorSettings, flake: bool) -> NixEvalCommand:
+def make_job_evaluator(name: str, settings: EvaluatorSettings, flake: bool, incoming_ref_data: dict[str, Any]) -> NixEvalCommand:
     actual_command = []
 
+    try:
+        eval_parameter_json_repr = json.dumps(incoming_ref_data)
+    except ValueError as e:
+        msg = f"Failed to serialize incoming ref data for {name}"
+        raise BuildbotNixError(msg) from e
+
     if flake:
         actual_command += ["--flake", f".#{FLAKE_TARGET_ATTRIBUTE_FOR_JOBS}"]
     else:
-        actual_command += ["--expr", "import ./.ci/buildbot.nix"]
+        # TODO: escape for Nix the JSON…
+        actual_command += ["--expr",
+                           f"import ./.ci/buildbot.nix {{ incoming_ref_data = ''{eval_parameter_json_repr}''; }}"]
 
     return NixEvalCommand(
         env={},
@@ -504,6 +512,14 @@ class NixConfigure(buildstep.CommandMixin, steps.BuildStep):
         except Exception:
             configure_log: Log = yield self.addLog("stdio")
 
+        # This information can be passed at job evaluation time
+        # to skip some jobs, e.g. expensive jobs, etc.
+        incoming_ref_data = {
+            # TODO: please just denormalize it properly.
+            'event': {
+                key: value for key, (value, _) in self.getProperties().asDict() if key.startswith('event.')
+            }
+        }
         # Takes precedence.
         configure_log.addStdout("checking if there's a .ci/buildbot.nix...\n")
         ci_buildbot_defn_exists = yield self.pathExists('build/.ci/buildbot.nix')
@@ -514,7 +530,8 @@ class NixConfigure(buildstep.CommandMixin, steps.BuildStep):
                     make_job_evaluator(
                         "evaluate `.ci/buildbot.nix` jobs",
                         self.evaluator_settings,
-                        False
+                        False,
+                        incoming_ref_data
                     )
                 ]
             )
@@ -527,7 +544,8 @@ class NixConfigure(buildstep.CommandMixin, steps.BuildStep):
                     make_job_evaluator(
                         "evaluate `flake.nix` jobs",
                         self.evaluator_settings,
-                        True
+                        True,
+                        incoming_ref_data
                     )
                 ]
             )