diff --git a/codex-rs/core/src/tools/handlers/multi_agents_spec_tests.rs b/codex-rs/core/src/tools/handlers/multi_agents_spec_tests.rs
index ad685919f9..d74729ef21 100644
--- a/codex-rs/core/src/tools/handlers/multi_agents_spec_tests.rs
+++ b/codex-rs/core/src/tools/handlers/multi_agents_spec_tests.rs
@@ -64,8 +64,8 @@ fn spawn_agent_tool_v2_requires_task_name() {
     );
     assert!(!properties.contains_key("service_tier"));
     assert_eq!(
-        parameters.required.as_ref(),
-        Some(&vec!["task_name".to_string(), "message".to_string()])
+        parameters.required.as_deref(),
+        Some(["task_name".to_string(), "message".to_string()].as_slice())
     );
     assert_eq!(
         output_schema.expect("spawn_agent output schema").to_value()["required"],
@@ -274,8 +274,8 @@ fn send_message_tool_requires_message_and_has_no_output_schema() {
         Some("Relative or canonical task name to message (from spawn_agent).")
     );
     assert_eq!(
-        parameters.required.as_ref(),
-        Some(&vec!["target".to_string(), "message".to_string()])
+        parameters.required.as_deref(),
+        Some(["target".to_string(), "message".to_string()].as_slice())
     );
     assert_eq!(output_schema, None);
 }
@@ -315,8 +315,8 @@ fn followup_task_tool_requires_message_and_has_no_output_schema() {
     );
     assert!(!properties.contains_key("items"));
     assert_eq!(
-        parameters.required.as_ref(),
-        Some(&vec!["target".to_string(), "message".to_string()])
+        parameters.required.as_deref(),
+        Some(["target".to_string(), "message".to_string()].as_slice())
     );
     assert_eq!(output_schema, None);
 }
diff --git a/codex-rs/core/src/tools/handlers/shell_spec.rs b/codex-rs/core/src/tools/handlers/shell_spec.rs
index ca48b21220..264a214f62 100644
--- a/codex-rs/core/src/tools/handlers/shell_spec.rs
+++ b/codex-rs/core/src/tools/handlers/shell_spec.rs
@@ -262,7 +262,7 @@ fn create_approval_parameters(
         let mut additional_permissions = permission_profile_schema();
         additional_permissions.description = Some(
             "Sandboxed filesystem or network access for this command; only with `sandbox_permissions: \"with_additional_permissions\"`."
-                .to_string(),
+                .into(),
         );
         properties.insert("additional_permissions".to_string(), additional_permissions);
     }
@@ -279,7 +279,7 @@ fn permission_profile_schema() -> JsonSchema {
         /*required*/ None,
         Some(false.into()),
     );
-    schema.description = Some("Filesystem or network access request.".to_string());
+    schema.description = Some("Filesystem or network access request.".into());
     schema
 }
 
@@ -294,7 +294,7 @@ fn network_permissions_schema() -> JsonSchema {
         /*required*/ None,
         Some(false.into()),
     );
-    schema.description = Some("Network access request.".to_string());
+    schema.description = Some("Network access request.".into());
     schema
 }
 
@@ -325,7 +325,7 @@ fn file_system_permissions_schema() -> JsonSchema {
         /*required*/ None,
         Some(false.into()),
     );
-    schema.description = Some("Filesystem access request.".to_string());
+    schema.description = Some("Filesystem access request.".into());
     schema
 }
 
diff --git a/codex-rs/core/src/tools/multi_agent_tool.rs b/codex-rs/core/src/tools/multi_agent_tool.rs
index 098e433646..0e44fd92b2 100644
--- a/codex-rs/core/src/tools/multi_agent_tool.rs
+++ b/codex-rs/core/src/tools/multi_agent_tool.rs
@@ -30,7 +30,7 @@ pub(super) fn multi_agent_v2_handler(
             && let Some(properties) = tool.parameters.properties
         {
             // Argument transport requires these markers even without server encryption config.
-            for (name, schema) in properties {
+            for (name, schema) in *properties {
                 if schema.encrypted == Some(true) {
                     let property = parameters
                         .properties
diff --git a/codex-rs/tools/src/json_schema/types.rs b/codex-rs/tools/src/json_schema/types.rs
index 0792816fd3..f7868bff04 100644
--- a/codex-rs/tools/src/json_schema/types.rs
+++ b/codex-rs/tools/src/json_schema/types.rs
@@ -29,49 +29,52 @@ pub enum JsonSchemaPrimitiveType {
 #[serde(untagged)]
 pub enum JsonSchemaType {
     Single(JsonSchemaPrimitiveType),
-    Multiple(Vec<JsonSchemaPrimitiveType>),
+    Multiple(Box<[JsonSchemaPrimitiveType]>),
 }
 
 /// Generic JSON-Schema subset needed for our tool definitions.
+///
+/// Stored strings and sequences do not grow, so they do not retain spare capacity.
+/// Optional maps are boxed because most schema nodes do not contain them.
 #[derive(Debug, Clone, Default, Serialize, Deserialize, PartialEq)]
 pub struct JsonSchema {
     /// Explicit ordinary MCP server input schema limit; never sent as JSON Schema.
     #[serde(skip)]
     pub mcp_input_schema_max_bytes: Option<usize>,
     #[serde(rename = "$ref", skip_serializing_if = "Option::is_none")]
-    pub schema_ref: Option<String>,
+    pub schema_ref: Option<Box<str>>,
     #[serde(rename = "type", skip_serializing_if = "Option::is_none")]
     pub schema_type: Option<JsonSchemaType>,
     #[serde(skip_serializing_if = "Option::is_none")]
-    pub description: Option<String>,
+    pub description: Option<Box<str>>,
     /// Responses-only marker for reviewed encrypted tool parameters.
     #[serde(skip_serializing_if = "Option::is_none")]
     pub encrypted: Option<bool>,
     #[serde(rename = "enum", skip_serializing_if = "Option::is_none")]
-    pub enum_values: Option<Vec<JsonValue>>,
+    pub enum_values: Option<Box<[JsonValue]>>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub items: Option<Box<JsonSchema>>,
     #[serde(rename = "minItems", skip_serializing_if = "Option::is_none")]
     pub min_items: Option<usize>,
     #[serde(skip_serializing_if = "Option::is_none")]
-    pub properties: Option<BTreeMap<String, JsonSchema>>,
+    pub properties: Option<Box<BTreeMap<String, JsonSchema>>>,
     #[serde(skip_serializing_if = "Option::is_none")]
-    pub required: Option<Vec<String>>,
+    pub required: Option<Box<[String]>>,
     #[serde(
         rename = "additionalProperties",
         skip_serializing_if = "Option::is_none"
     )]
     pub additional_properties: Option<AdditionalProperties>,
     #[serde(rename = "anyOf", skip_serializing_if = "Option::is_none")]
-    pub any_of: Option<Vec<JsonSchema>>,
+    pub any_of: Option<Box<[JsonSchema]>>,
     #[serde(rename = "oneOf", skip_serializing_if = "Option::is_none")]
-    pub one_of: Option<Vec<JsonSchema>>,
+    pub one_of: Option<Box<[JsonSchema]>>,
     #[serde(rename = "allOf", skip_serializing_if = "Option::is_none")]
-    pub all_of: Option<Vec<JsonSchema>>,
+    pub all_of: Option<Box<[JsonSchema]>>,
     #[serde(rename = "$defs", skip_serializing_if = "Option::is_none")]
-    pub defs: Option<BTreeMap<String, JsonSchema>>,
+    pub defs: Option<Box<BTreeMap<String, JsonSchema>>>,
     #[serde(skip_serializing_if = "Option::is_none")]
-    pub definitions: Option<BTreeMap<String, JsonSchema>>,
+    pub definitions: Option<Box<BTreeMap<String, JsonSchema>>>,
 }
 
 impl JsonSchema {
@@ -79,31 +82,31 @@ impl JsonSchema {
     fn typed(schema_type: JsonSchemaPrimitiveType, description: Option<String>) -> Self {
         Self {
             schema_type: Some(JsonSchemaType::Single(schema_type)),
-            description,
+            description: description.map(String::into_boxed_str),
             ..Default::default()
         }
     }
 
     pub fn any_of(variants: Vec<JsonSchema>, description: Option<String>) -> Self {
         Self {
-            description,
-            any_of: Some(variants),
+            description: description.map(String::into_boxed_str),
+            any_of: Some(variants.into_boxed_slice()),
             ..Default::default()
         }
     }
 
     pub fn one_of(variants: Vec<JsonSchema>, description: Option<String>) -> Self {
         Self {
-            description,
-            one_of: Some(variants),
+            description: description.map(String::into_boxed_str),
+            one_of: Some(variants.into_boxed_slice()),
             ..Default::default()
         }
     }
 
     pub fn all_of(variants: Vec<JsonSchema>, description: Option<String>) -> Self {
         Self {
-            description,
-            all_of: Some(variants),
+            description: description.map(String::into_boxed_str),
+            all_of: Some(variants.into_boxed_slice()),
             ..Default::default()
         }
     }
@@ -136,8 +139,8 @@ impl JsonSchema {
     pub fn string_enum(values: Vec<JsonValue>, description: Option<String>) -> Self {
         Self {
             schema_type: Some(JsonSchemaType::Single(JsonSchemaPrimitiveType::String)),
-            description,
-            enum_values: Some(values),
+            description: description.map(String::into_boxed_str),
+            enum_values: Some(values.into_boxed_slice()),
             ..Default::default()
         }
     }
@@ -145,7 +148,7 @@ impl JsonSchema {
     pub fn array(items: JsonSchema, description: Option<String>) -> Self {
         Self {
             schema_type: Some(JsonSchemaType::Single(JsonSchemaPrimitiveType::Array)),
-            description,
+            description: description.map(String::into_boxed_str),
             items: Some(Box::new(items)),
             ..Default::default()
         }
@@ -158,8 +161,8 @@ impl JsonSchema {
     ) -> Self {
         Self {
             schema_type: Some(JsonSchemaType::Single(JsonSchemaPrimitiveType::Object)),
-            properties: Some(properties),
-            required,
+            properties: Some(Box::new(properties)),
+            required: required.map(Vec::into_boxed_slice),
             additional_properties,
             ..Default::default()
         }
diff --git a/codex-rs/tools/src/json_schema_tests.rs b/codex-rs/tools/src/json_schema_tests.rs
index 449631475d..768ae2deee 100644
--- a/codex-rs/tools/src/json_schema_tests.rs
+++ b/codex-rs/tools/src/json_schema_tests.rs
@@ -479,11 +479,11 @@ fn parse_tool_input_schema_fills_default_properties_for_nullable_object_union()
     assert_eq!(
         schema,
         JsonSchema {
-            schema_type: Some(JsonSchemaType::Multiple(vec![
+            schema_type: Some(JsonSchemaType::Multiple(Box::new([
                 JsonSchemaPrimitiveType::Object,
                 JsonSchemaPrimitiveType::Null,
-            ])),
-            properties: Some(BTreeMap::new()),
+            ]))),
+            properties: Some(Box::default()),
             ..Default::default()
         }
     );
@@ -507,10 +507,10 @@ fn parse_tool_input_schema_fills_default_items_for_nullable_array_union() {
     assert_eq!(
         schema,
         JsonSchema {
-            schema_type: Some(JsonSchemaType::Multiple(vec![
+            schema_type: Some(JsonSchemaType::Multiple(Box::new([
                 JsonSchemaPrimitiveType::Array,
                 JsonSchemaPrimitiveType::Null,
-            ])),
+            ]))),
             items: Some(Box::new(JsonSchema::string(/*description*/ None))),
             ..Default::default()
         }
@@ -650,11 +650,11 @@ fn parse_tool_input_schema_preserves_nested_nullable_type_union() {
             BTreeMap::from([(
                 "nickname".to_string(),
                 JsonSchema {
-                    schema_type: Some(JsonSchemaType::Multiple(vec![
+                    schema_type: Some(JsonSchemaType::Multiple(Box::new([
                         JsonSchemaPrimitiveType::String,
                         JsonSchemaPrimitiveType::Null,
-                    ])),
-                    description: Some("Optional nickname".to_string()),
+                    ]))),
+                    description: Some("Optional nickname".into()),
                     ..Default::default()
                 },
             )]),
@@ -837,11 +837,11 @@ fn parse_tool_input_schema_preserves_type_unions_without_rewriting_to_any_of() {
     assert_eq!(
         schema,
         JsonSchema {
-            schema_type: Some(JsonSchemaType::Multiple(vec![
+            schema_type: Some(JsonSchemaType::Multiple(Box::new([
                 JsonSchemaPrimitiveType::String,
                 JsonSchemaPrimitiveType::Null,
-            ])),
-            description: Some("optional string".to_string()),
+            ]))),
+            description: Some("optional string".into()),
             ..Default::default()
         }
     );
@@ -868,16 +868,16 @@ fn parse_tool_input_schema_preserves_explicit_enum_type_union() {
     assert_eq!(
         schema,
         JsonSchema {
-            schema_type: Some(JsonSchemaType::Multiple(vec![
+            schema_type: Some(JsonSchemaType::Multiple(Box::new([
                 JsonSchemaPrimitiveType::String,
                 JsonSchemaPrimitiveType::Null,
-            ])),
-            description: Some("optional response length".to_string()),
-            enum_values: Some(vec![
+            ]))),
+            description: Some("optional response length".into()),
+            enum_values: Some(Box::new([
                 serde_json::json!("short"),
                 serde_json::json!("medium"),
                 serde_json::json!("long"),
-            ]),
+            ])),
             ..Default::default()
         }
     );
@@ -1382,14 +1382,14 @@ fn parse_tool_input_schema_preserves_refs_and_prunes_unreachable_defs() {
         schema,
         JsonSchema {
             schema_type: Some(JsonSchemaType::Single(JsonSchemaPrimitiveType::Object)),
-            properties: Some(BTreeMap::from([(
+            properties: Some(Box::new(BTreeMap::from([(
                 "user".to_string(),
                 JsonSchema {
-                    schema_ref: Some("#/$defs/User".to_string()),
+                    schema_ref: Some("#/$defs/User".into()),
                     ..Default::default()
                 },
-            )])),
-            defs: Some(BTreeMap::from([(
+            )]))),
+            defs: Some(Box::new(BTreeMap::from([(
                 "User".to_string(),
                 JsonSchema::object(
                     BTreeMap::from([(
@@ -1399,7 +1399,7 @@ fn parse_tool_input_schema_preserves_refs_and_prunes_unreachable_defs() {
                     /*required*/ None,
                     /*additional_properties*/ None,
                 ),
-            )])),
+            )]))),
             ..Default::default()
         }
     );
@@ -1437,17 +1437,17 @@ fn parse_tool_input_schema_preserves_refs_from_properties_named_def_tables() {
         schema,
         JsonSchema {
             schema_type: Some(JsonSchemaType::Single(JsonSchemaPrimitiveType::Object)),
-            properties: Some(BTreeMap::from([(
+            properties: Some(Box::new(BTreeMap::from([(
                 "$defs".to_string(),
                 JsonSchema {
-                    schema_ref: Some("#/$defs/User".to_string()),
+                    schema_ref: Some("#/$defs/User".into()),
                     ..Default::default()
                 },
-            )])),
-            defs: Some(BTreeMap::from([(
+            )]))),
+            defs: Some(Box::new(BTreeMap::from([(
                 "User".to_string(),
                 JsonSchema::string(/*description*/ None),
-            )])),
+            )]))),
             ..Default::default()
         }
     );
@@ -1578,27 +1578,27 @@ fn parse_tool_input_schema_handles_cyclic_local_refs() {
         schema,
         JsonSchema {
             schema_type: Some(JsonSchemaType::Single(JsonSchemaPrimitiveType::Object)),
-            properties: Some(BTreeMap::from([(
+            properties: Some(Box::new(BTreeMap::from([(
                 "node".to_string(),
                 JsonSchema {
-                    schema_ref: Some("#/$defs/Node".to_string()),
+                    schema_ref: Some("#/$defs/Node".into()),
                     ..Default::default()
                 },
-            )])),
-            defs: Some(BTreeMap::from([(
+            )]))),
+            defs: Some(Box::new(BTreeMap::from([(
                 "Node".to_string(),
                 JsonSchema::object(
                     BTreeMap::from([(
                         "next".to_string(),
                         JsonSchema {
-                            schema_ref: Some("#/$defs/Node".to_string()),
+                            schema_ref: Some("#/$defs/Node".into()),
                             ..Default::default()
                         },
                     )]),
                     /*required*/ None,
                     /*additional_properties*/ None,
                 ),
-            )])),
+            )]))),
             ..Default::default()
         }
     );
@@ -1647,14 +1647,14 @@ fn parse_tool_input_schema_preserves_legacy_definitions() {
         schema,
         JsonSchema {
             schema_type: Some(JsonSchemaType::Single(JsonSchemaPrimitiveType::Object)),
-            properties: Some(BTreeMap::from([(
+            properties: Some(Box::new(BTreeMap::from([(
                 "user".to_string(),
                 JsonSchema {
-                    schema_ref: Some("#/definitions/User".to_string()),
+                    schema_ref: Some("#/definitions/User".into()),
                     ..Default::default()
                 },
-            )])),
-            definitions: Some(BTreeMap::from([
+            )]))),
+            definitions: Some(Box::new(BTreeMap::from([
                 (
                     "Profile".to_string(),
                     JsonSchema::object(
@@ -1672,7 +1672,7 @@ fn parse_tool_input_schema_preserves_legacy_definitions() {
                         BTreeMap::from([(
                             "profile".to_string(),
                             JsonSchema {
-                                schema_ref: Some("#/definitions/Profile".to_string()),
+                                schema_ref: Some("#/definitions/Profile".into()),
                                 ..Default::default()
                             },
                         )]),
@@ -1680,7 +1680,7 @@ fn parse_tool_input_schema_preserves_legacy_definitions() {
                         /*additional_properties*/ None,
                     ),
                 ),
-            ])),
+            ]))),
             ..Default::default()
         }
     );
@@ -1718,22 +1718,22 @@ fn parse_tool_input_schema_preserves_unresolved_and_external_refs() {
         schema,
         JsonSchema {
             schema_type: Some(JsonSchemaType::Single(JsonSchemaPrimitiveType::Object)),
-            properties: Some(BTreeMap::from([
+            properties: Some(Box::new(BTreeMap::from([
                 (
                     "missing".to_string(),
                     JsonSchema {
-                        schema_ref: Some("#/$defs/Missing".to_string()),
+                        schema_ref: Some("#/$defs/Missing".into()),
                         ..Default::default()
                     },
                 ),
                 (
                     "remote".to_string(),
                     JsonSchema {
-                        schema_ref: Some("https://example.com/schema.json".to_string()),
+                        schema_ref: Some("https://example.com/schema.json".into()),
                         ..Default::default()
                     },
                 ),
-            ])),
+            ]))),
             ..Default::default()
         }
     );
@@ -1778,14 +1778,14 @@ fn parse_tool_input_schema_preserves_nested_defs_ref_parent() {
         schema,
         JsonSchema {
             schema_type: Some(JsonSchemaType::Single(JsonSchemaPrimitiveType::Object)),
-            properties: Some(BTreeMap::from([(
+            properties: Some(Box::new(BTreeMap::from([(
                 "name".to_string(),
                 JsonSchema {
-                    schema_ref: Some("#/$defs/User/properties/name".to_string()),
+                    schema_ref: Some("#/$defs/User/properties/name".into()),
                     ..Default::default()
                 },
-            )])),
-            defs: Some(BTreeMap::from([(
+            )]))),
+            defs: Some(Box::new(BTreeMap::from([(
                 "User".to_string(),
                 JsonSchema::object(
                     BTreeMap::from([(
@@ -1795,7 +1795,7 @@ fn parse_tool_input_schema_preserves_nested_defs_ref_parent() {
                     /*required*/ None,
                     /*additional_properties*/ None,
                 ),
-            )])),
+            )]))),
             ..Default::default()
         }
     );
@@ -1840,23 +1840,23 @@ fn parse_tool_input_schema_preserves_percent_encoded_definition_refs() {
         schema,
         JsonSchema {
             schema_type: Some(JsonSchemaType::Single(JsonSchemaPrimitiveType::Object)),
-            properties: Some(BTreeMap::from([
+            properties: Some(Box::new(BTreeMap::from([
                 (
                     "profile".to_string(),
                     JsonSchema {
-                        schema_ref: Some("#/%24defs/Profile%7E0Name".to_string()),
+                        schema_ref: Some("#/%24defs/Profile%7E0Name".into()),
                         ..Default::default()
                     },
                 ),
                 (
                     "user".to_string(),
                     JsonSchema {
-                        schema_ref: Some("#/$defs/User%20Name".to_string()),
+                        schema_ref: Some("#/$defs/User%20Name".into()),
                         ..Default::default()
                     },
                 ),
-            ])),
-            defs: Some(BTreeMap::from([
+            ]))),
+            defs: Some(Box::new(BTreeMap::from([
                 (
                     "Profile~Name".to_string(),
                     JsonSchema::string(/*description*/ None),
@@ -1865,7 +1865,7 @@ fn parse_tool_input_schema_preserves_percent_encoded_definition_refs() {
                     "User Name".to_string(),
                     JsonSchema::string(/*description*/ None),
                 ),
-            ])),
+            ]))),
             ..Default::default()
         }
     );
@@ -1896,13 +1896,13 @@ fn parse_tool_input_schema_drops_malformed_definition_tables() {
         schema,
         JsonSchema {
             schema_type: Some(JsonSchemaType::Single(JsonSchemaPrimitiveType::Object)),
-            properties: Some(BTreeMap::from([(
+            properties: Some(Box::new(BTreeMap::from([(
                 "user".to_string(),
                 JsonSchema {
-                    schema_ref: Some("#/$defs/User".to_string()),
+                    schema_ref: Some("#/$defs/User".into()),
                     ..Default::default()
                 },
-            )])),
+            )]))),
             ..Default::default()
         }
     );
diff --git a/codex-rs/tools/src/tool_search.rs b/codex-rs/tools/src/tool_search.rs
index 829910ea8f..c25daad32f 100644
--- a/codex-rs/tools/src/tool_search.rs
+++ b/codex-rs/tools/src/tool_search.rs
@@ -177,9 +177,9 @@ fn append_function_search_text(tool: &ResponsesApiTool, parts: &mut Vec<String>)
 
 fn append_schema_search_text(schema: &JsonSchema, parts: &mut Vec<String>) {
     if let Some(description) = &schema.description {
-        push_search_part(parts, description.clone());
+        push_search_part(parts, description.to_string());
     }
-    if let Some(properties) = &schema.properties {
+    if let Some(properties) = schema.properties.as_deref() {
         for (name, schema) in properties {
             push_search_part(parts, name.clone());
             append_schema_search_text(schema, parts);
diff --git a/codex-rs/tools/src/tool_search_tests.rs b/codex-rs/tools/src/tool_search_tests.rs
index 9e34967e59..3d654aa8e6 100644
--- a/codex-rs/tools/src/tool_search_tests.rs
+++ b/codex-rs/tools/src/tool_search_tests.rs
@@ -180,7 +180,7 @@ fn default_search_text_uses_model_visible_namespace_metadata_once() {
         /*required*/ None,
         /*additional_properties*/ None,
     );
-    schedule_schema.description = Some("Schedule settings.".to_string());
+    schedule_schema.description = Some("Schedule settings.".into());
     let mut parameters = JsonSchema::object(
         BTreeMap::from([
             (
@@ -192,7 +192,7 @@ fn default_search_text_uses_model_visible_namespace_metadata_once() {
         /*required*/ None,
         /*additional_properties*/ None,
     );
-    parameters.description = Some("Automation options.".to_string());
+    parameters.description = Some("Automation options.".into());
     let spec = ToolSpec::Namespace(crate::ResponsesApiNamespace {
         name: "codex_app".to_string(),
         description: "Manage Codex automations.".to_string(),