From 4948a9d2737fa7d2f5ad5a2f64ddf65fb0acf849 Mon Sep 17 00:00:00 2001
From: arun <arun@openai.com>
Date: Tue, 26 May 2026 19:01:52 +0000
Subject: [PATCH] Hide app-only MCP tools from model

---
 codex-rs/codex-mcp/src/tools.rs             | 19 +++++++
 codex-rs/core/src/mcp_tool_exposure.rs      |  9 ++-
 codex-rs/core/src/mcp_tool_exposure_test.rs | 61 +++++++++++++++++++++
 3 files changed, 87 insertions(+), 2 deletions(-)

diff --git a/codex-rs/codex-mcp/src/tools.rs b/codex-rs/codex-mcp/src/tools.rs
index 83cbfd5e74..7767fac2c0 100644
--- a/codex-rs/codex-mcp/src/tools.rs
+++ b/codex-rs/codex-mcp/src/tools.rs
@@ -59,6 +59,22 @@ impl ToolInfo {
     pub fn canonical_tool_name(&self) -> ToolName {
         ToolName::namespaced(self.callable_namespace.clone(), self.callable_name.clone())
     }
+
+    /// Returns whether MCP Apps metadata allows this tool to be presented to the model.
+    pub fn is_model_visible(&self) -> bool {
+        self.tool
+            .meta
+            .as_deref()
+            .and_then(|meta| meta.get(META_UI))
+            .and_then(JsonValue::as_object)
+            .and_then(|ui| ui.get(META_UI_VISIBILITY))
+            .and_then(JsonValue::as_array)
+            .is_none_or(|visibility| {
+                visibility
+                    .iter()
+                    .any(|value| value.as_str() == Some(META_UI_VISIBILITY_MODEL))
+            })
+    }
 }
 
 pub fn declared_openai_file_input_param_names(
@@ -261,6 +277,9 @@ const MCP_TOOL_NAME_DELIMITER: &str = "__";
 const MAX_TOOL_NAME_LENGTH: usize = 64;
 const CALLABLE_NAME_HASH_LEN: usize = 12;
 const META_OPENAI_FILE_PARAMS: &str = "openai/fileParams";
+const META_UI: &str = "ui";
+const META_UI_VISIBILITY: &str = "visibility";
+const META_UI_VISIBILITY_MODEL: &str = "model";
 
 fn callable_namespace_with_prefix(namespace: &str, prefix_mcp_tool_names: bool) -> String {
     if !prefix_mcp_tool_names || namespace.starts_with(LEGACY_MCP_TOOL_NAME_PREFIX) {
diff --git a/codex-rs/core/src/mcp_tool_exposure.rs b/codex-rs/core/src/mcp_tool_exposure.rs
index e58be65f9c..e544133d61 100644
--- a/codex-rs/core/src/mcp_tool_exposure.rs
+++ b/codex-rs/core/src/mcp_tool_exposure.rs
@@ -20,10 +20,15 @@ pub(crate) fn build_mcp_tool_exposure(
     config: &Config,
     search_tool_enabled: bool,
 ) -> McpToolExposure {
-    let mut deferred_tools = filter_non_codex_apps_mcp_tools_only(all_mcp_tools);
+    let model_visible_tools = all_mcp_tools
+        .iter()
+        .filter(|tool| tool.is_model_visible())
+        .cloned()
+        .collect::<Vec<_>>();
+    let mut deferred_tools = filter_non_codex_apps_mcp_tools_only(&model_visible_tools);
     if let Some(connectors) = connectors {
         deferred_tools.extend(filter_codex_apps_mcp_tools(
-            all_mcp_tools,
+            &model_visible_tools,
             connectors,
             config,
         ));
diff --git a/codex-rs/core/src/mcp_tool_exposure_test.rs b/codex-rs/core/src/mcp_tool_exposure_test.rs
index 367baaf4a0..95be76aeeb 100644
--- a/codex-rs/core/src/mcp_tool_exposure_test.rs
+++ b/codex-rs/core/src/mcp_tool_exposure_test.rs
@@ -7,6 +7,7 @@ use codex_mcp::ToolInfo;
 use codex_tools::ToolName;
 use pretty_assertions::assert_eq;
 use rmcp::model::JsonObject;
+use rmcp::model::Meta;
 use rmcp::model::Tool;
 
 use super::*;
@@ -79,6 +80,20 @@ fn numbered_mcp_tools(count: usize) -> Vec<ToolInfo> {
         .collect()
 }
 
+fn with_ui_visibility(mut tool: ToolInfo, visibility: &[&str]) -> ToolInfo {
+    tool.tool.meta = Some(Meta(
+        serde_json::json!({
+            "ui": {
+                "visibility": visibility,
+            },
+        })
+        .as_object()
+        .expect("object")
+        .clone(),
+    ));
+    tool
+}
+
 fn tool_names(tools: &[ToolInfo]) -> HashSet<ToolName> {
     tools
         .iter()
@@ -86,6 +101,52 @@ fn tool_names(tools: &[ToolInfo]) -> HashSet<ToolName> {
         .collect()
 }
 
+#[tokio::test]
+async fn hides_app_only_tools_from_model_exposure() {
+    let config = test_config().await;
+    let public_tool = make_mcp_tool(
+        "rmcp",
+        "public_tool",
+        "mcp__rmcp",
+        "public_tool",
+        /*connector_id*/ None,
+        /*connector_name*/ None,
+    );
+    let app_only_tool = with_ui_visibility(
+        make_mcp_tool(
+            "rmcp",
+            "app_only_tool",
+            "mcp__rmcp",
+            "app_only_tool",
+            /*connector_id*/ None,
+            /*connector_name*/ None,
+        ),
+        &["app"],
+    );
+    let model_only_tool = with_ui_visibility(
+        make_mcp_tool(
+            "rmcp",
+            "model_only_tool",
+            "mcp__rmcp",
+            "model_only_tool",
+            /*connector_id*/ None,
+            /*connector_name*/ None,
+        ),
+        &["model"],
+    );
+    let mcp_tools = vec![public_tool.clone(), app_only_tool, model_only_tool.clone()];
+
+    let exposure = build_mcp_tool_exposure(
+        &mcp_tools, /*connectors*/ None, &config, /*search_tool_enabled*/ true,
+    );
+
+    assert_eq!(
+        tool_names(&exposure.direct_tools),
+        tool_names(&[public_tool, model_only_tool])
+    );
+    assert!(exposure.deferred_tools.is_none());
+}
+
 #[tokio::test]
 async fn directly_exposes_small_effective_tool_sets() {
     let config = test_config().await;