diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4ce0a74ac..541d2e980 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,20 @@
 # Changelog
 
-## [v0.3.0] - 2025-06-10
+## [v0.3.1] - 2025-06-10
+
+### Added
+- New pytest marker `dry_runnable` for tests that can run without inference.
+- Enhanced `make` targets with dry-run capabilities for improved test coverage:
+  - `make test-xdist` (or `make t`): Runs all non-inference tests **plus inference tests** that support dry-runs - fast and resource-efficient
+  - `make test-inference` (or `make ti`): Runs tests requiring actual inference, with actual inference (slow and costly)
+- Parallel test execution using `pytest-xdist` (`-n auto`) enabled for:
+  - GitHub Actions workflows
+  - Codex test targets
+  
+### Changed
+- Domain validation is now less restrictive in pipeline TOML: the `definition` attribute is now `Optional`
+
+## [v0.3.0] - 2025-06-09
 
 ### Highlights
 
diff --git a/Makefile b/Makefile
index fc6c08af4..4366989f3 100644
--- a/Makefile
+++ b/Makefile
@@ -16,6 +16,8 @@ VENV_PIPELEX := $(VIRTUAL_ENV)/bin/pipelex
 
 UV_MIN_VERSION = $(shell grep -m1 'required-version' pyproject.toml | sed -E 's/.*= *"([^<>=, ]+).*/\1/')
 
+USUAL_PYTEST_MARKERS := "(dry_runnable or not (inference or llm or imgg or ocr)) and not (needs_output or pipelex_api)"
+
 define PRINT_TITLE
     $(eval PROJECT_PART := [$(PROJECT_NAME)])
     $(eval TARGET_PART := ($@))
@@ -203,17 +205,17 @@ cleanall: cleanderived cleanenv cleanlibraries
 codex-tests: env
 	$(call PRINT_TITLE,"Unit testing for Codex")
 	@echo "• Running unit tests for Codex (excluding inference and codex_disabled)"
-	$(VENV_PYTEST) --exitfirst --quiet -m "not (inference or codex_disabled or pipelex_api)" || [ $$? = 5 ]
+	$(VENV_PYTEST) -n auto --exitfirst --quiet -m "(dry_runnable or not inference) and not (needs_output or pipelex_api)" || [ $$? = 5 ]
 
 gha-tests: env
 	$(call PRINT_TITLE,"Unit testing for github actions")
 	@echo "• Running unit tests for github actions (excluding inference and gha_disabled)"
-	$(VENV_PYTEST) --exitfirst --quiet -m "not (inference or gha_disabled or pipelex_api)" || [ $$? = 5 ]
+	$(VENV_PYTEST) -n auto --exitfirst --quiet -m "(dry_runnable or not inference) and not (gha_disabled or pipelex_api)" || [ $$? = 5 ]
 
 run-all-tests: env
 	$(call PRINT_TITLE,"Running all unit tests")
 	@echo "• Running all unit tests"
-	$(VENV_PYTEST) --exitfirst --quiet
+	$(VENV_PYTEST) -n auto --exitfirst --quiet
 
 run-manual-trigger-gha-tests: env
 	$(call PRINT_TITLE,"Running GHA tests")
@@ -229,18 +231,18 @@ test: env
 	$(call PRINT_TITLE,"Unit testing without prints but displaying logs via pytest for WARNING level and above")
 	@echo "• Running unit tests"
 	@if [ -n "$(TEST)" ]; then \
-		$(VENV_PYTEST) -s -o log_cli=true -o log_level=WARNING -k "$(TEST)" $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
+		$(VENV_PYTEST) -s -m $(USUAL_PYTEST_MARKERS) -o log_cli=true -o log_level=WARNING -k "$(TEST)" $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
 	else \
-		$(VENV_PYTEST) -s -o log_cli=true -o log_level=WARNING $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
+		$(VENV_PYTEST) -s -m $(USUAL_PYTEST_MARKERS) -o log_cli=true -o log_level=WARNING $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
 	fi
 
 test-xdist: env
 	$(call PRINT_TITLE,"Unit testing without prints but displaying logs via pytest for WARNING level and above")
 	@echo "• Running unit tests"
 	@if [ -n "$(TEST)" ]; then \
-		$(VENV_PYTEST) -n auto -o log_level=WARNING -k "$(TEST)" $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
+		$(VENV_PYTEST) -n auto -m $(USUAL_PYTEST_MARKERS) -o log_level=WARNING -k "$(TEST)" $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
 	else \
-		$(VENV_PYTEST) -n auto -o log_level=WARNING $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
+		$(VENV_PYTEST) -n auto -m $(USUAL_PYTEST_MARKERS) -o log_level=WARNING $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
 	fi
 
 t: test-xdist
@@ -250,9 +252,9 @@ test-quiet: env
 	$(call PRINT_TITLE,"Unit testing without prints but displaying logs via pytest for WARNING level and above")
 	@echo "• Running unit tests"
 	@if [ -n "$(TEST)" ]; then \
-		$(VENV_PYTEST) -o log_cli=true -o log_level=WARNING -k "$(TEST)" $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
+		$(VENV_PYTEST) -m $(USUAL_PYTEST_MARKERS) -o log_cli=true -o log_level=WARNING -k "$(TEST)" $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
 	else \
-		$(VENV_PYTEST) -o log_cli=true -o log_level=WARNING $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
+		$(VENV_PYTEST) -m $(USUAL_PYTEST_MARKERS) -o log_cli=true -o log_level=WARNING $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
 	fi
 
 tq: test-quiet
@@ -262,9 +264,9 @@ test-with-prints: env
 	$(call PRINT_TITLE,"Unit testing with prints and our rich logs")
 	@echo "• Running unit tests"
 	@if [ -n "$(TEST)" ]; then \
-		$(VENV_PYTEST) -s -k "$(TEST)" $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
+		$(VENV_PYTEST) -s -m $(USUAL_PYTEST_MARKERS) -k "$(TEST)" $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
 	else \
-		$(VENV_PYTEST) -s $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
+		$(VENV_PYTEST) -s -m $(USUAL_PYTEST_MARKERS) $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
 	fi
 
 tp: test-with-prints
@@ -273,9 +275,9 @@ tp: test-with-prints
 test-inference: env
 	$(call PRINT_TITLE,"Unit testing")
 	@if [ -n "$(TEST)" ]; then \
-		$(VENV_PYTEST) --exitfirst -m "inference and not imgg" -s -k "$(TEST)" $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
+		$(VENV_PYTEST) --pipe-run-mode live --exitfirst -m "inference and not imgg" -s -k "$(TEST)" $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
 	else \
-		$(VENV_PYTEST) --exitfirst -m "inference and not imgg" -s $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
+		$(VENV_PYTEST) --pipe-run-mode live --exitfirst -m "inference and not imgg" -s $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
 	fi
 
 ti: test-inference
@@ -284,9 +286,9 @@ ti: test-inference
 test-ocr: env
 	$(call PRINT_TITLE,"Unit testing ocr")
 	@if [ -n "$(TEST)" ]; then \
-		$(VENV_PYTEST) --exitfirst -m "ocr" -s -k "$(TEST)" $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
+		$(VENV_PYTEST) --pipe-run-mode live --exitfirst -m "ocr" -s -k "$(TEST)" $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
 	else \
-		$(VENV_PYTEST) --exitfirst -m "ocr" -s $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
+		$(VENV_PYTEST) --pipe-run-mode live --exitfirst -m "ocr" -s $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
 	fi
 
 to: test-ocr
@@ -295,9 +297,9 @@ to: test-ocr
 test-imgg: env
 	$(call PRINT_TITLE,"Unit testing")
 	@if [ -n "$(TEST)" ]; then \
-		$(VENV_PYTEST) --exitfirst -m "imgg" -s -k "$(TEST)" $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
+		$(VENV_PYTEST) --pipe-run-mode live --exitfirst -m "imgg" -s -k "$(TEST)" $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
 	else \
-		$(VENV_PYTEST) --exitfirst -m "imgg" -s $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
+		$(VENV_PYTEST) --pipe-run-mode live --exitfirst -m "imgg" -s $(if $(filter 1,$(VERBOSE)),-v,$(if $(filter 2,$(VERBOSE)),-vv,$(if $(filter 3,$(VERBOSE)),-vvv,))); \
 	fi
 
 tg: test-imgg
diff --git a/pipelex/core/domain.py b/pipelex/core/domain.py
index 3d2081c3c..04cfbd35d 100644
--- a/pipelex/core/domain.py
+++ b/pipelex/core/domain.py
@@ -13,7 +13,7 @@ class SpecialDomain(StrEnum):
 
 class Domain(BaseModel):
     code: str
-    definition: str
+    definition: Optional[str] = None
     system_prompt: Optional[str] = None
     system_prompt_to_structure: Optional[str] = None
     prompt_template_to_structure: Optional[str] = None
@@ -24,4 +24,4 @@ def __str__(self):
 
     @classmethod
     def make_default(cls) -> Self:
-        return cls(code=SpecialDomain.NATIVE, definition="")
+        return cls(code=SpecialDomain.NATIVE)
diff --git a/pipelex/libraries/library_manager.py b/pipelex/libraries/library_manager.py
index 1871e70ff..f527f9f75 100644
--- a/pipelex/libraries/library_manager.py
+++ b/pipelex/libraries/library_manager.py
@@ -128,7 +128,10 @@ def _load_combo_libraries(self, library_paths: List[str]):
             library_name = toml_path.stem
             domain_code = library_dict.get("domain")
             if domain_code is None:
-                raise LibraryParsingError(f"Error loafing library '{library_name}' which has no domain set at '{toml_path}'")
+                raise LibraryParsingError(
+                    f"Error loading library '{library_name}' which has no domain set at '{toml_path}'. "
+                    "Just write 'domain = \"my_domain\"' at the top of the file."
+                )
             domain_definition = library_dict.get("definition")
             if domain_definition is None:
                 # we skip the domain without definition, it must be defined one and only one time in the domain library
@@ -177,10 +180,6 @@ def _load_combo_libraries(self, library_paths: List[str]):
 
     def _load_library_dict(self, library_name: str, library_dict: Dict[str, Any], component_type: LibraryComponent):
         if domain_code := library_dict.pop("domain", None):
-            if not self.domain_library.get_domain(domain_code=domain_code):
-                raise LibraryParsingError(
-                    f"Domain '{domain_code}' is has not been defined in the domain libraryn make sure it has exactlyone definition"
-                )
             # domain is set at the root of the library
             self._load_library_components_from_recursive_dict(
                 domain_code=domain_code,
diff --git a/pipelex/pipelex.toml b/pipelex/pipelex.toml
index d7a47ff48..79431a752 100644
--- a/pipelex/pipelex.toml
+++ b/pipelex/pipelex.toml
@@ -244,4 +244,4 @@ pipe_stack_limit = 20
 
 [pipelex.dry_run_config]
 apply_to_jinja2_rendering = false
-text_gen_truncate_length = 256
\ No newline at end of file
+text_gen_truncate_length = 256
diff --git a/pyproject.toml b/pyproject.toml
index 252d88222..1130c1845 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "pipelex"
-version = "0.3.0"
+version = "0.3.1"
 description = "Pipelex is an open-source dev tool based on a simple declarative language that lets you define replicable, structured, composable LLM pipelines."
 authors = [{ name = "Evotis S.A.S.", email = "evotis@pipelex.com" }]
 maintainers = [{ name = "Pipelex staff", email = "oss@pipelex.com" }]
@@ -208,6 +208,7 @@ markers = [
     "ocr: slow and costly due to ocr inference calls",
     "gha_disabled: tests that should not run in GitHub Actions",
     "codex_disabled: tests that should not run in Codex",
+    "dry_runnable: tests that can be run in dry-run mode",
 ]
 minversion = "8.0"
 
diff --git a/tests/pipelex/pipelex_asynch/test_pipe_batch.py b/tests/pipelex/pipelex_asynch/test_pipe_batch.py
index d2b9eb4a3..be772c723 100644
--- a/tests/pipelex/pipelex_asynch/test_pipe_batch.py
+++ b/tests/pipelex/pipelex_asynch/test_pipe_batch.py
@@ -10,6 +10,7 @@
 from pipelex.hub import get_pipe_router, get_pipeline_tracker, get_report_delegate
 
 
+@pytest.mark.dry_runnable
 @pytest.mark.llm
 @pytest.mark.inference
 @pytest.mark.asyncio(loop_scope="class")
diff --git a/tests/pipelex/pipelex_asynch/test_pipe_imgg.py b/tests/pipelex/pipelex_asynch/test_pipe_imgg.py
index ad501bcfb..3ef3e5f71 100644
--- a/tests/pipelex/pipelex_asynch/test_pipe_imgg.py
+++ b/tests/pipelex/pipelex_asynch/test_pipe_imgg.py
@@ -11,6 +11,7 @@
 from tests.pipelex.test_data import IMGGTestCases
 
 
+@pytest.mark.dry_runnable
 @pytest.mark.imgg
 @pytest.mark.inference
 @pytest.mark.asyncio(loop_scope="class")
diff --git a/tests/pipelex/pipelex_asynch/test_pipe_llm.py b/tests/pipelex/pipelex_asynch/test_pipe_llm.py
index 6b895a69d..86535a7ca 100644
--- a/tests/pipelex/pipelex_asynch/test_pipe_llm.py
+++ b/tests/pipelex/pipelex_asynch/test_pipe_llm.py
@@ -16,6 +16,7 @@
 from tests.pipelex.test_data import PipeTestCases
 
 
+@pytest.mark.dry_runnable
 @pytest.mark.llm
 @pytest.mark.inference
 @pytest.mark.asyncio(loop_scope="class")
diff --git a/tests/pipelex/pipelex_asynch/test_pipe_ocr.py b/tests/pipelex/pipelex_asynch/test_pipe_ocr.py
index 9ebe82096..349da9321 100644
--- a/tests/pipelex/pipelex_asynch/test_pipe_ocr.py
+++ b/tests/pipelex/pipelex_asynch/test_pipe_ocr.py
@@ -13,6 +13,7 @@
 from tests.pipelex.test_data import PipeOcrTestCases
 
 
+@pytest.mark.dry_runnable
 @pytest.mark.ocr
 @pytest.mark.inference
 @pytest.mark.asyncio(loop_scope="class")
diff --git a/tests/pipelex/pipelex_asynch/test_pipe_running_variants.py b/tests/pipelex/pipelex_asynch/test_pipe_running_variants.py
index ba7ab0c20..023a733e7 100644
--- a/tests/pipelex/pipelex_asynch/test_pipe_running_variants.py
+++ b/tests/pipelex/pipelex_asynch/test_pipe_running_variants.py
@@ -17,6 +17,7 @@
 from tests.pipelex.test_data import PipeTestCases
 
 
+@pytest.mark.dry_runnable
 @pytest.mark.llm
 @pytest.mark.ocr
 @pytest.mark.inference
diff --git a/tests/test_pipelines/failure_modes.toml b/tests/test_pipelines/failure_modes.toml
index 6abb942ea..a46283c99 100644
--- a/tests/test_pipelines/failure_modes.toml
+++ b/tests/test_pipelines/failure_modes.toml
@@ -1,7 +1,6 @@
 
 
 domain = "failure_modes"
-definition = "This domain is for testing failure modes"
 
 [concept]