diff --git a/execution.py b/execution.py
index c45317593..00e4c2aae 100644
--- a/execution.py
+++ b/execution.py
@@ -1113,6 +1113,32 @@ def full_type_name(klass):
         return klass.__qualname__
     return module + '.' + klass.__qualname__
 
+def node_not_executable_reason(class_def, class_type):
+    """Return a human-readable reason the node cannot be executed, or None if it's fine.
+
+    Catches a node whose declared entry point doesn't resolve to a real method
+    (e.g. a V1 ``FUNCTION = "invert"`` where the method is misspelled, or a V3 node
+    missing its ``execute`` override). Running this during validation surfaces the
+    problem before execution starts, instead of after upstream nodes have run.
+
+    Only the class is inspected; the node is never instantiated here, so a node's
+    ``__init__`` side effects cannot run (or fail) during validation.
+    """
+    try:
+        if issubclass(class_def, _ComfyNodeInternal):
+            # V3: validates that execute()/define_schema() overrides exist.
+            class_def.VALIDATE_CLASS()
+            return None
+        # V1: FUNCTION names the method to call; it must exist on the class.
+        function_name = getattr(class_def, "FUNCTION", None)
+        if function_name is None:
+            return f"'{class_type}' does not define FUNCTION"
+        if not callable(getattr(class_def, function_name, None)):
+            return f"'{class_type}' has no method '{function_name}' (declared in FUNCTION)"
+        return None
+    except Exception as ex:
+        return str(ex)
+
 async def validate_prompt(prompt_id, prompt, partial_execution_list: Union[list[str], None]):
     outputs = set()
     for x in prompt:
@@ -1148,6 +1174,35 @@ async def validate_prompt(prompt_id, prompt, partial_execution_list: Union[list[
             }
             return (False, error, [], {})
 
+        # Make sure the node is actually executable (its FUNCTION/execute entry
+        # point resolves to a real method) before we touch any schema-derived
+        # attributes below or start execution. Catches code typos up front and
+        # attributes the error to the offending node.
+        not_executable = node_not_executable_reason(class_, class_type)
+        if not_executable is not None:
+            node_title = prompt[x].get('_meta', {}).get('title', class_type)
+            error = {
+                "type": "invalid_node_definition",
+                "message": "Node is not executable",
+                "details": f"{not_executable} (Node ID '#{x}')",
+                "extra_info": {
+                    "node_id": x,
+                    "class_type": class_type,
+                    "node_title": node_title,
+                }
+            }
+            node_errors = {x: {
+                "errors": [{
+                    "type": "invalid_node_definition",
+                    "message": "Node is not executable",
+                    "details": not_executable,
+                    "extra_info": {},
+                }],
+                "dependent_outputs": [],
+                "class_type": class_type,
+            }}
+            return (False, error, [], node_errors)
+
         if hasattr(class_, 'OUTPUT_NODE') and class_.OUTPUT_NODE is True:
             if partial_execution_list is None or x in partial_execution_list:
                 outputs.add(x)
diff --git a/tests-unit/execution_test/validate_node_executable_test.py b/tests-unit/execution_test/validate_node_executable_test.py
new file mode 100644
index 000000000..694163b58
--- /dev/null
+++ b/tests-unit/execution_test/validate_node_executable_test.py
@@ -0,0 +1,137 @@
+"""Tests for pre-execution validation that a node is actually executable.
+
+validate_prompt rejects a node whose declared entry point does not resolve to a
+real method (a V1 FUNCTION typo, or a V3 node missing its execute override) before
+any node runs, attributing the error to the offending node.
+"""
+import asyncio
+
+import nodes
+from comfy_api.latest import io
+from execution import node_not_executable_reason, validate_prompt
+
+
+class _GoodV1Node:
+    @classmethod
+    def INPUT_TYPES(cls):
+        return {"required": {}}
+
+    RETURN_TYPES = ("IMAGE",)
+    FUNCTION = "run"
+    OUTPUT_NODE = True
+    CATEGORY = "Test"
+
+    def run(self):
+        return (None,)
+
+
+class _TypoV1Node:
+    @classmethod
+    def INPUT_TYPES(cls):
+        return {"required": {}}
+
+    RETURN_TYPES = ("IMAGE",)
+    FUNCTION = "invert"  # method below is misspelled
+    OUTPUT_NODE = True
+    CATEGORY = "Test"
+
+    def invvert(self):
+        return (None,)
+
+
+class _SideEffectInitV1Node:
+    """Valid class-level method, but a constructor that must never run in validation."""
+    @classmethod
+    def INPUT_TYPES(cls):
+        return {"required": {}}
+
+    RETURN_TYPES = ("IMAGE",)
+    FUNCTION = "run"
+    OUTPUT_NODE = True
+    CATEGORY = "Test"
+
+    def __init__(self):
+        raise RuntimeError("__init__ must not run during validation")
+
+    def run(self):
+        return (None,)
+
+
+def _v3_schema(node_id):
+    return io.Schema(
+        node_id=node_id,
+        display_name=node_id,
+        category="Test",
+        inputs=[],
+        outputs=[io.Image.Output()],
+        is_output_node=True,
+    )
+
+
+class _GoodV3Node(io.ComfyNode):
+    @classmethod
+    def define_schema(cls):
+        return _v3_schema("GoodV3Node")
+
+    @classmethod
+    def execute(cls):
+        return io.NodeOutput(None)
+
+
+class _TypoV3Node(io.ComfyNode):
+    @classmethod
+    def define_schema(cls):
+        return _v3_schema("TypoV3Node")
+
+    @classmethod
+    def exicute(cls):  # typo: should be "execute"
+        return io.NodeOutput(None)
+
+
+def _register(class_type, class_def):
+    nodes.NODE_CLASS_MAPPINGS[class_type] = class_def
+
+
+def _validate(class_type):
+    prompt = {"1": {"class_type": class_type, "inputs": {}}}
+    return asyncio.run(validate_prompt("pid", prompt, None))
+
+
+def test_good_node_passes():
+    _register("GoodV1Node", _GoodV1Node)
+    assert node_not_executable_reason(_GoodV1Node, "GoodV1Node") is None
+    valid, _, _, _ = _validate("GoodV1Node")
+    assert valid is True
+
+
+def test_typo_node_rejected_with_node_error():
+    _register("TypoV1Node", _TypoV1Node)
+    valid, error, _, node_errors = _validate("TypoV1Node")
+    assert valid is False
+    assert error["type"] == "invalid_node_definition"
+    assert node_errors["1"]["class_type"] == "TypoV1Node"
+    assert node_errors["1"]["errors"][0]["type"] == "invalid_node_definition"
+    assert "invert" in node_errors["1"]["errors"][0]["details"]
+
+
+def test_validation_does_not_instantiate_node():
+    """A valid node is not constructed during validation, so __init__ never runs."""
+    _register("SideEffectInitV1Node", _SideEffectInitV1Node)
+    assert node_not_executable_reason(_SideEffectInitV1Node, "SideEffectInitV1Node") is None
+    valid, _, _, _ = _validate("SideEffectInitV1Node")
+    assert valid is True
+
+
+def test_good_v3_node_passes():
+    _register("GoodV3Node", _GoodV3Node)
+    assert node_not_executable_reason(_GoodV3Node, "GoodV3Node") is None
+    valid, _, _, _ = _validate("GoodV3Node")
+    assert valid is True
+
+
+def test_typo_v3_node_rejected_with_node_error():
+    _register("TypoV3Node", _TypoV3Node)
+    valid, error, _, node_errors = _validate("TypoV3Node")
+    assert valid is False
+    assert error["type"] == "invalid_node_definition"
+    assert node_errors["1"]["errors"][0]["type"] == "invalid_node_definition"