diff --git a/src/goose/toolkit/developer.py b/src/goose/toolkit/developer.py
index 062b1b40..450ce244 100644
--- a/src/goose/toolkit/developer.py
+++ b/src/goose/toolkit/developer.py
@@ -1,6 +1,7 @@
 from pathlib import Path
 from subprocess import CompletedProcess, run
-from typing import List
+from typing import List, Dict
+import os
 from goose.utils.check_shell_command import is_dangerous_command
 
 from exchange import Message
@@ -30,6 +31,10 @@ class Developer(Toolkit):
     We also include some default shell strategies in the prompt, such as using ripgrep
     """
 
+    def __init__(self, *args: object, **kwargs: Dict[str, object]) -> None:
+        super().__init__(*args, **kwargs)
+        self.timestamps: Dict[str, float] = {}
+
     def system(self) -> str:
         """Retrieve system configuration details for developer"""
         hints_path = Path(".goosehints")
@@ -65,7 +70,7 @@ def update_plan(self, tasks: List[dict]) -> List[dict]:
         table.add_column("Status", justify="left")
 
         # Mapping of statuses to emojis for better visual representation in the table.
-        emoji = {"planned": "⏳", "complete": "✅", "failed": "❌", "in-progress": "🕓"}
+        emoji = {"planned": "⏳", "complete": "✅", "failed": "❌", "in-progress": "🕑"}
         for i, entry in enumerate(tasks):
             table.add_row(str(i), entry["description"], emoji[entry["status"]])
 
@@ -124,6 +129,8 @@ def read_file(self, path: str) -> str:
         language = get_language(path)
         content = Path(path).expanduser().read_text()
         self.notifier.log(Panel.fit(Markdown(f"```\ncat {path}\n```"), box=box.MINIMAL))
+        # Record the last read timestamp
+        self.timestamps[path] = os.path.getmtime(path)
         return f"```{language}\n{content}\n```"
 
     @tool
@@ -183,12 +190,24 @@ def write_file(self, path: str, content: str) -> str:
         # this method is dynamically attached to functions in the Goose framework
         self.notifier.log(Panel.fit(Markdown(md), title=path))
 
-        # Prepare the path and create any necessary parent directories
         _path = Path(path)
+        if path in self.timestamps:
+            last_read_timestamp = self.timestamps.get(path, 0.0)
+            current_timestamp = os.path.getmtime(path)
+            if current_timestamp > last_read_timestamp:
+                raise RuntimeError(
+                    f"File '{path}' has been modified since it was last read."
+                    + " Read the file to incorporate changes or update your plan."
+                )
+
+        # Prepare the path and create any necessary parent directories
         _path.parent.mkdir(parents=True, exist_ok=True)
 
         # Write the content to the file
         _path.write_text(content)
 
+        # Update the last read timestamp after writing to the file
+        self.timestamps[path] = os.path.getmtime(path)
+
         # Return a success message
-        return f"Succesfully wrote to {path}"
+        return f"Successfully wrote to {path}"
diff --git a/tests/toolkit/test_developer.py b/tests/toolkit/test_developer.py
index a3a291af..e36c498c 100644
--- a/tests/toolkit/test_developer.py
+++ b/tests/toolkit/test_developer.py
@@ -93,3 +93,24 @@ def test_write_file(temp_dir, developer_toolkit):
     content = "Hello World"
     developer_toolkit.write_file(test_file.as_posix(), content)
     assert test_file.read_text() == content
+
+
+def test_write_file_prevent_write_if_changed(temp_dir, developer_toolkit):
+    test_file = temp_dir / "test.txt"
+    content = "Hello World"
+    updated_content = "Hello Universe"
+
+    # Initial write to record the timestamp
+    developer_toolkit.write_file(test_file.as_posix(), content)
+    developer_toolkit.read_file(test_file.as_posix())
+
+    import time
+
+    # Modify file externally to simulate change
+    time.sleep(1)
+    test_file.write_text(updated_content)
+
+    # Try to write through toolkit and check for the raised exception
+    with pytest.raises(RuntimeError, match="has been modified"):
+        developer_toolkit.write_file(test_file.as_posix(), content)
+    assert test_file.read_text() == updated_content