diff --git a/codex-rs/ext/memories/src/lib.rs b/codex-rs/ext/memories/src/lib.rs
index d17c4c4956..25120c7a3a 100644
--- a/codex-rs/ext/memories/src/lib.rs
+++ b/codex-rs/ext/memories/src/lib.rs
@@ -15,7 +15,7 @@ pub(crate) const MAX_SEARCH_RESULTS: usize = 200;
 pub(crate) const DEFAULT_READ_MAX_TOKENS: usize = 20_000;
 pub(crate) const MEMORY_TOOL_DEVELOPER_INSTRUCTIONS_SUMMARY_TOKEN_LIMIT: usize = 2_500;
 
-pub(crate) const MEMORY_TOOLS_NAMESPACE: &str = "memories/";
+pub(crate) const MEMORY_TOOLS_NAMESPACE: &str = "memories";
 pub(crate) const ADD_AD_HOC_NOTE_TOOL_NAME: &str = "add_ad_hoc_note";
 pub(crate) const LIST_TOOL_NAME: &str = "list";
 pub(crate) const READ_TOOL_NAME: &str = "read";
diff --git a/codex-rs/ext/memories/src/metrics.rs b/codex-rs/ext/memories/src/metrics.rs
index 610a3cb9ed..443156b724 100644
--- a/codex-rs/ext/memories/src/metrics.rs
+++ b/codex-rs/ext/memories/src/metrics.rs
@@ -15,7 +15,7 @@ pub(crate) fn record_tool_call(
         return;
     };
 
-    let tool = format!("{MEMORY_TOOLS_NAMESPACE}{operation}");
+    let tool = format!("{MEMORY_TOOLS_NAMESPACE}/{operation}");
     let _ = metrics_client.counter(
         MEMORIES_TOOL_CALL_METRIC,
         /*inc*/ 1,
diff --git a/codex-rs/ext/memories/src/tests.rs b/codex-rs/ext/memories/src/tests.rs
index fbb23bd7ac..b70c5f802d 100644
--- a/codex-rs/ext/memories/src/tests.rs
+++ b/codex-rs/ext/memories/src/tests.rs
@@ -22,6 +22,16 @@ use crate::extension::MemoriesExtension;
 use crate::extension::MemoriesExtensionConfig;
 use crate::local::LocalMemoriesBackend;
 
+#[test]
+fn memory_tool_namespace_matches_responses_api_identifier() {
+    assert!(!crate::MEMORY_TOOLS_NAMESPACE.is_empty());
+    assert!(
+        crate::MEMORY_TOOLS_NAMESPACE
+            .bytes()
+            .all(|byte| byte.is_ascii_alphanumeric() || matches!(byte, b'_' | b'-'))
+    );
+}
+
 #[test]
 fn tools_are_not_contributed_without_thread_config() {
     let extension = MemoriesExtension::default();