diff --git a/langchain/tools/zapier/tool.py b/langchain/tools/zapier/tool.py
index f68a3562..cb1fc295 100644
--- a/langchain/tools/zapier/tool.py
+++ b/langchain/tools/zapier/tool.py
@@ -105,6 +105,7 @@ class ZapierNLARunAction(BaseTool):
     api_wrapper: ZapierNLAWrapper = Field(default_factory=ZapierNLAWrapper)
     action_id: str
     params: Optional[dict] = None
+    base_prompt: str = BASE_ZAPIER_TOOL_PROMPT
     zapier_description: str
     params_schema: Dict[str, str] = Field(default_factory=dict)
     name = ""
@@ -116,8 +117,17 @@ class ZapierNLARunAction(BaseTool):
         params_schema = values["params_schema"]
         if "instructions" in params_schema:
             del params_schema["instructions"]
+
+        # Ensure base prompt (if overrided) contains necessary input fields
+        necessary_fields = {"{zapier_description}", "{params}"}
+        if not all(field in values["base_prompt"] for field in necessary_fields):
+            raise ValueError(
+                "Your custom base Zapier prompt must contain input fields for "
+                "{zapier_description} and {params}."
+            )
+
         values["name"] = zapier_description
-        values["description"] = BASE_ZAPIER_TOOL_PROMPT.format(
+        values["description"] = values["base_prompt"].format(
             zapier_description=zapier_description,
             params=str(list(params_schema.keys())),
         )
diff --git a/tests/unit_tests/tools/test_zapier.py b/tests/unit_tests/tools/test_zapier.py
new file mode 100644
index 00000000..a4b60be9
--- /dev/null
+++ b/tests/unit_tests/tools/test_zapier.py
@@ -0,0 +1,52 @@
+"""Test building the Zapier tool, not running it."""
+import pytest
+
+from langchain.tools.zapier.prompt import BASE_ZAPIER_TOOL_PROMPT
+from langchain.tools.zapier.tool import ZapierNLARunAction
+from langchain.utilities.zapier import ZapierNLAWrapper
+
+
+def test_default_base_prompt() -> None:
+    """Test that the default prompt is being inserted."""
+    tool = ZapierNLARunAction(
+        action_id="test",
+        zapier_description="test",
+        params_schema={"test": "test"},
+        api_wrapper=ZapierNLAWrapper(zapier_nla_api_key="test"),
+    )
+
+    # Test that the base prompt was successfully assigned to the default prompt
+    assert tool.base_prompt == BASE_ZAPIER_TOOL_PROMPT
+    assert tool.description == BASE_ZAPIER_TOOL_PROMPT.format(
+        zapier_description="test",
+        params=str(list({"test": "test"}.keys())),
+    )
+
+
+def test_custom_base_prompt() -> None:
+    """Test that a custom prompt is being inserted."""
+    base_prompt = "Test. {zapier_description} and {params}."
+    tool = ZapierNLARunAction(
+        action_id="test",
+        zapier_description="test",
+        params_schema={"test": "test"},
+        base_prompt=base_prompt,
+        api_wrapper=ZapierNLAWrapper(zapier_nla_api_key="test"),
+    )
+
+    # Test that the base prompt was successfully assigned to the default prompt
+    assert tool.base_prompt == base_prompt
+    assert tool.description == "Test. test and ['test']."
+
+
+def test_custom_base_prompt_fail() -> None:
+    """Test validating an invalid custom prompt."""
+    base_prompt = "Test. {zapier_description}."
+    with pytest.raises(ValueError):
+        ZapierNLARunAction(
+            action_id="test",
+            zapier_description="test",
+            params={"test": "test"},
+            base_prompt=base_prompt,
+            api_wrapper=ZapierNLAWrapper(zapier_nla_api_key="test"),
+        )