diff --git a/utoipa/src/openapi/info.rs b/utoipa/src/openapi/info.rs
index 967f7ea3..a4b3d5df 100644
--- a/utoipa/src/openapi/info.rs
+++ b/utoipa/src/openapi/info.rs
@@ -6,6 +6,8 @@
 //! [info]: <https://spec.openapis.org/oas/latest.html#info-object>
 //! [openapi_trait]: ../../trait.OpenApi.html
 //! [derive]: ../../derive.OpenApi.html
+use std::collections::HashMap;
+
 use serde::{Deserialize, Serialize};
 
 use super::{builder, set_value};
@@ -66,6 +68,10 @@ builder! {
 
         /// Document version typically the API version.
         pub version: String,
+
+        /// Optional extensions "x-something"
+        #[serde(skip_serializing_if = "Option::is_none", flatten)]
+        pub extensions: Option<HashMap<String, serde_json::Value>>,
     }
 }
 
@@ -120,6 +126,11 @@ impl InfoBuilder {
     pub fn license(mut self, license: Option<License>) -> Self {
         set_value!(self license license)
     }
+
+    /// Add openapi extensions (x-something) of the API.
+    pub fn extensions(mut self, extensions: Option<HashMap<String, serde_json::Value>>) -> Self {
+        set_value!(self extensions extensions)
+    }
 }
 
 builder! {
diff --git a/utoipa/src/openapi/path.rs b/utoipa/src/openapi/path.rs
index f3a53874..c81acc4f 100644
--- a/utoipa/src/openapi/path.rs
+++ b/utoipa/src/openapi/path.rs
@@ -1,7 +1,7 @@
 //! Implements [OpenAPI Path Object][paths] types.
 //!
 //! [paths]: https://spec.openapis.org/oas/latest.html#paths-object
-use std::iter;
+use std::{collections::HashMap, iter};
 
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
@@ -34,6 +34,10 @@ builder! {
         /// Map of relative paths with [`PathItem`]s holding [`Operation`]s matching
         /// api endpoints.
         pub paths: PathsMap<String, PathItem>,
+
+        /// Optional extensions "x-something"
+        #[serde(skip_serializing_if = "Option::is_none", flatten)]
+        pub extensions: Option<HashMap<String, serde_json::Value>>,
     }
 }
 
@@ -97,6 +101,11 @@ impl PathsBuilder {
 
         self
     }
+
+    /// Add extensions to the paths section.
+    pub fn extensions(mut self, extensions: Option<HashMap<String, serde_json::Value>>) -> Self {
+        set_value!(self extensions extensions)
+    }
 }
 
 builder! {
@@ -135,6 +144,10 @@ builder! {
         /// per [`PathItemType`].
         #[serde(flatten)]
         pub operations: PathsMap<PathItemType, Operation>,
+
+        /// Optional extensions "x-something"
+        #[serde(skip_serializing_if = "Option::is_none", flatten)]
+        pub extensions: Option<HashMap<String, serde_json::Value>>,
     }
 }
 
@@ -184,6 +197,11 @@ impl PathItemBuilder {
     pub fn parameters<I: IntoIterator<Item = Parameter>>(mut self, parameters: Option<I>) -> Self {
         set_value!(self parameters parameters.map(|parameters| parameters.into_iter().collect()))
     }
+
+    /// Add openapi extensions (x-something) to this [`PathItem`].
+    pub fn extensions(mut self, extensions: Option<HashMap<String, serde_json::Value>>) -> Self {
+        set_value!(self extensions extensions)
+    }
 }
 
 /// Path item operation type.
@@ -295,6 +313,10 @@ builder! {
         /// Alternative [`Server`]s for this [`Operation`].
         #[serde(skip_serializing_if = "Option::is_none")]
         pub servers: Option<Vec<Server>>,
+
+        /// Optional extensions "x-something"
+        #[serde(skip_serializing_if = "Option::is_none", flatten)]
+        pub extensions: Option<HashMap<String, serde_json::Value>>,
     }
 }
 
@@ -436,6 +458,11 @@ impl OperationBuilder {
 
         self
     }
+
+    /// Add openapi extensions (x-something) of the [`Operation`].
+    pub fn extensions(mut self, extensions: Option<HashMap<String, serde_json::Value>>) -> Self {
+        set_value!(self extensions extensions)
+    }
 }
 
 builder! {
@@ -506,6 +533,10 @@ builder! {
         /// within [`Parameter::schema`] if defined.
         #[serde(skip_serializing_if = "Option::is_none")]
         example: Option<Value>,
+
+        /// Optional extensions "x-something"
+        #[serde(skip_serializing_if = "Option::is_none", flatten)]
+        pub extensions: Option<HashMap<String, serde_json::Value>>,
     }
 }
 
@@ -577,6 +608,11 @@ impl ParameterBuilder {
     pub fn example(mut self, example: Option<Value>) -> Self {
         set_value!(self example example)
     }
+
+    /// Add openapi extensions (x-something) to the [`Parameter`].
+    pub fn extensions(mut self, extensions: Option<HashMap<String, serde_json::Value>>) -> Self {
+        set_value!(self extensions extensions)
+    }
 }
 
 /// In definition of [`Parameter`].
diff --git a/utoipa/src/openapi/response.rs b/utoipa/src/openapi/response.rs
index 9b0f1409..a75eb183 100644
--- a/utoipa/src/openapi/response.rs
+++ b/utoipa/src/openapi/response.rs
@@ -1,7 +1,7 @@
 //! Implements [OpenApi Responses][responses].
 //!
 //! [responses]: https://spec.openapis.org/oas/latest.html#responses-object
-use std::collections::BTreeMap;
+use std::collections::{BTreeMap, HashMap};
 
 use indexmap::IndexMap;
 use serde::{Deserialize, Serialize};
@@ -118,6 +118,10 @@ builder! {
         /// will create and show default example according to the first entry in `content` map.
         #[serde(skip_serializing_if = "IndexMap::is_empty", default)]
         pub content: IndexMap<String, Content>,
+
+        /// Optional extensions "x-something"
+        #[serde(skip_serializing_if = "Option::is_none", flatten)]
+        pub extensions: Option<HashMap<String, serde_json::Value>>,
     }
 }
 
@@ -152,6 +156,11 @@ impl ResponseBuilder {
 
         self
     }
+
+    /// Add openapi extensions (x-something) to the [`Header`].
+    pub fn extensions(mut self, extensions: Option<HashMap<String, serde_json::Value>>) -> Self {
+        set_value!(self extensions extensions)
+    }
 }
 
 impl From<ResponseBuilder> for RefOr<Response> {
diff --git a/utoipa/src/openapi/security.rs b/utoipa/src/openapi/security.rs
index bb86a0be..f5011d99 100644
--- a/utoipa/src/openapi/security.rs
+++ b/utoipa/src/openapi/security.rs
@@ -3,7 +3,10 @@
 //! Refer to [`SecurityScheme`] for usage and more details.
 //!
 //! [security]: https://spec.openapis.org/oas/latest.html#security-scheme-object
-use std::{collections::BTreeMap, iter};
+use std::{
+    collections::{BTreeMap, HashMap},
+    iter,
+};
 
 use serde::{Deserialize, Serialize};
 
@@ -352,6 +355,10 @@ pub struct OAuth2 {
     /// Optional description for the [`OAuth2`] [`Flow`] [`SecurityScheme`].
     #[serde(skip_serializing_if = "Option::is_none")]
     pub description: Option<String>,
+
+    /// Optional extensions "x-something"
+    #[serde(skip_serializing_if = "Option::is_none", flatten)]
+    pub extensions: Option<HashMap<String, serde_json::Value>>,
 }
 
 impl OAuth2 {
@@ -391,6 +398,7 @@ impl OAuth2 {
                     .into_iter()
                     .map(|auth_flow| (String::from(auth_flow.get_type_as_str()), auth_flow)),
             ),
+            extensions: None,
             description: None,
         }
     }
@@ -433,6 +441,7 @@ impl OAuth2 {
                     .into_iter()
                     .map(|auth_flow| (String::from(auth_flow.get_type_as_str()), auth_flow)),
             ),
+            extensions: None,
             description: Some(description.into()),
         }
     }
diff --git a/utoipa/src/openapi/tag.rs b/utoipa/src/openapi/tag.rs
index e232801c..d2ee6a8f 100644
--- a/utoipa/src/openapi/tag.rs
+++ b/utoipa/src/openapi/tag.rs
@@ -1,6 +1,8 @@
 //! Implements [OpenAPI Tag Object][tag] types.
 //!
 //! [tag]: https://spec.openapis.org/oas/latest.html#tag-object
+use std::collections::HashMap;
+
 use serde::{Deserialize, Serialize};
 
 use super::{builder, external_docs::ExternalDocs, set_value};
@@ -28,6 +30,10 @@ builder! {
         /// Additional external documentation for the tag.
         #[serde(skip_serializing_if = "Option::is_none")]
         pub external_docs: Option<ExternalDocs>,
+
+        /// Optional extensions "x-something"
+        #[serde(skip_serializing_if = "Option::is_none", flatten)]
+        pub extensions: Option<HashMap<String, serde_json::Value>>,
     }
 }
 
@@ -56,4 +62,9 @@ impl TagBuilder {
     pub fn external_docs(mut self, external_docs: Option<ExternalDocs>) -> Self {
         set_value!(self external_docs external_docs)
     }
+
+    /// Add openapi extensions (x-something) to the tag.
+    pub fn extensions(mut self, extensions: Option<HashMap<String, serde_json::Value>>) -> Self {
+        set_value!(self extensions extensions)
+    }
 }