diff --git a/guard/src/rules/eval_context.rs b/guard/src/rules/eval_context.rs
index 1ff1216b..1ba80b00 100644
--- a/guard/src/rules/eval_context.rs
+++ b/guard/src/rules/eval_context.rs
@@ -1194,6 +1194,7 @@ pub(crate) enum FunctionName {
     ToLower,
     ToUpper,
     UrlDecode,
+    Key, // <-- add this line
 }
 
 impl FunctionName {
@@ -1213,6 +1214,7 @@ impl FunctionName {
             | FunctionName::ParseEpoch
             | FunctionName::ParseChar => 1,
             FunctionName::Now => 0,
+            FunctionName::Key => 1, // key expects 1 argument
         }
     }
 }
@@ -1235,6 +1237,7 @@ impl std::fmt::Display for FunctionName {
             FunctionName::ToLower => "to_lower",
             FunctionName::ToUpper => "to_upper",
             FunctionName::UrlDecode => "url_decode",
+            FunctionName::Key => "key",
         };
         write!(f, "{}", name)
     }
@@ -1260,6 +1263,7 @@ impl TryFrom<&str> for FunctionName {
             "to_lower" => Ok(FunctionName::ToLower),
             "to_upper" => Ok(FunctionName::ToUpper),
             "url_decode" => Ok(FunctionName::UrlDecode),
+            "key" => Ok(FunctionName::Key),
             _ => Err(Error::ParseError(format!(
                 "No function with the name '{name}' exists.",
             ))),
@@ -1282,6 +1286,7 @@ struct ParseBooleanFunction;
 struct ParseCharFunction;
 struct ParseEpochFunction;
 struct NowFunction;
+struct KeyFunction;
 
 trait Callable {
     fn call(&self, args: &[Vec<QueryResult>]) -> Result<Vec<Option<PathAwareValue>>>;
@@ -1305,6 +1310,7 @@ impl Callable for FunctionName {
             FunctionName::ParseChar => ParseCharFunction.call(args),
             FunctionName::ParseEpoch => ParseEpochFunction.call(args),
             FunctionName::Now => NowFunction.call(args),
+            FunctionName::Key => KeyFunction.call(args),
         }
     }
 }
@@ -2471,6 +2477,13 @@ pub(crate) fn resolve_function<'value, 'eval, 'loc: 'value>(
         .collect::<Vec<_>>())
 }
 
+impl Callable for KeyFunction {
+    fn call(&self, args: &[Vec<QueryResult>]) -> Result<Vec<Option<PathAwareValue>>> {
+        use crate::rules::functions::key::key;
+        Ok(vec![Some(key(&args[0]))])
+    }
+}
+
 #[cfg(test)]
 #[path = "eval_context_tests.rs"]
 pub(super) mod eval_context_tests;
diff --git a/guard/src/rules/functions.rs b/guard/src/rules/functions.rs
index 8dc36276..d31b788d 100644
--- a/guard/src/rules/functions.rs
+++ b/guard/src/rules/functions.rs
@@ -1,4 +1,5 @@
 pub(crate) mod collections;
 pub mod converters;
 pub mod date_time;
+pub(crate) mod key;
 pub(crate) mod strings;
diff --git a/guard/src/rules/functions/key.rs b/guard/src/rules/functions/key.rs
new file mode 100644
index 00000000..5fec3135
--- /dev/null
+++ b/guard/src/rules/functions/key.rs
@@ -0,0 +1,27 @@
+use crate::rules::path_value::{Path, PathAwareValue};
+use crate::rules::QueryResult;
+
+#[cfg(test)]
+#[path = "key_tests.rs"]
+mod key_tests;
+
+pub(crate) fn key(args: &[QueryResult]) -> PathAwareValue {
+    // Return the key (logical id) for the first resolved argument
+    for arg in args {
+        match arg {
+            QueryResult::Resolved(val) | QueryResult::Literal(val) => {
+                let path = val.self_path();
+                // Use relative() to get the last segment/key
+                let key = path.relative();
+                return PathAwareValue::String((path.clone(), key.to_string()));
+            }
+            QueryResult::UnResolved(unresolved) => {
+                let path = unresolved.traversed_to.self_path();
+                let key = path.relative();
+                return PathAwareValue::String((path.clone(), key.to_string()));
+            }
+        }
+    }
+    // If no key found, return empty string at root
+    PathAwareValue::String((Path::root(), String::new()))
+}
diff --git a/guard/src/rules/functions/key_tests.rs b/guard/src/rules/functions/key_tests.rs
new file mode 100644
index 00000000..8acb2b66
--- /dev/null
+++ b/guard/src/rules/functions/key_tests.rs
@@ -0,0 +1,27 @@
+#[cfg(test)]
+use crate::rules::functions::key;
+use crate::rules::path_value::{Path, PathAwareValue};
+use crate::rules::QueryResult;
+use std::rc::Rc;
+
+#[test]
+fn test_key_function_returns_last_segment() {
+    let path = Path::new("/Resources/MyBucket".to_string(), 0, 0);
+    let value = PathAwareValue::String((path.clone(), "test-value".to_string()));
+    let result = key::key(&[QueryResult::Resolved(Rc::new(value))]);
+    if let PathAwareValue::String((_, key_str)) = result {
+        assert_eq!(key_str, "MyBucket");
+    } else {
+        panic!("Expected String result");
+    }
+}
+
+#[test]
+fn test_key_function_empty_args() {
+    let result = key::key(&[]);
+    if let PathAwareValue::String((_, key_str)) = result {
+        assert_eq!(key_str, "");
+    } else {
+        panic!("Expected String result");
+    }
+}