diff --git a/crates/matrix-sdk/Cargo.toml b/crates/matrix-sdk/Cargo.toml
index 9ecf5d38c9d..155d4e8c4d6 100644
--- a/crates/matrix-sdk/Cargo.toml
+++ b/crates/matrix-sdk/Cargo.toml
@@ -55,6 +55,7 @@ experimental-sliding-sync = [
     "reqwest/gzip",
     "dep:eyeball-im-util",
 ]
+experimental-widget-api = []
 
 docsrs = ["e2e-encryption", "sqlite", "sso-login", "qrcode", "image-proc"]
 
diff --git a/crates/matrix-sdk/src/lib.rs b/crates/matrix-sdk/src/lib.rs
index ecadc8c710b..ad0057f6eef 100644
--- a/crates/matrix-sdk/src/lib.rs
+++ b/crates/matrix-sdk/src/lib.rs
@@ -34,6 +34,8 @@ pub mod attachment;
 mod authentication;
 mod client;
 pub mod config;
+#[cfg(feature = "e2e-encryption")]
+pub mod encryption;
 mod error;
 pub mod event_handler;
 mod http_client;
@@ -43,13 +45,12 @@ pub mod notification_settings;
 #[cfg(feature = "experimental-oidc")]
 pub mod oidc;
 pub mod room;
-pub mod sync;
-
 #[cfg(feature = "experimental-sliding-sync")]
 pub mod sliding_sync;
+pub mod sync;
+#[cfg(feature = "experimental-widget-api")]
+pub mod widget;
 
-#[cfg(feature = "e2e-encryption")]
-pub mod encryption;
 pub use account::Account;
 pub use authentication::{AuthApi, AuthSession};
 pub use client::{Client, ClientBuildError, ClientBuilder, LoopCtrl, SendRequest, UnknownToken};
diff --git a/crates/matrix-sdk/src/widget/mod.rs b/crates/matrix-sdk/src/widget/mod.rs
new file mode 100644
index 00000000000..aab47402d6d
--- /dev/null
+++ b/crates/matrix-sdk/src/widget/mod.rs
@@ -0,0 +1,52 @@
+//! Client widget API implementation.
+
+use tokio::sync::mpsc::{Receiver, Sender};
+
+use crate::room::Room as JoinedRoom;
+
+mod permissions;
+
+pub use self::permissions::{Permissions, PermissionsProvider};
+
+/// Describes a widget.
+#[derive(Debug)]
+pub struct Widget {
+    /// Information about the widget.
+    pub info: Info,
+    /// Communication channels with a widget.
+    pub comm: Comm,
+}
+
+/// Information about a widget.
+#[derive(Debug)]
+pub struct Info {
+    /// Widget's unique identifier.
+    pub id: String,
+    /// Whether or not the widget should be initialized on load message
+    /// (`ContentLoad` message), or upon creation/attaching of the widget to
+    /// the SDK's state machine that drives the API.
+    pub init_on_load: bool,
+}
+
+/// Communication "pipes" with a widget.
+#[derive(Debug)]
+pub struct Comm {
+    /// Raw incoming messages from the widget (normally, formatted as JSON).
+    pub from: Receiver<String>,
+    /// Raw outgoing messages from the client (SDK) to the widget (normally
+    /// formatted as JSON).
+    pub to: Sender<String>,
+}
+
+/// Starts a client widget API state machine for a given `widget` in a given
+/// joined `room`. The function returns once the widget is disconnected or any
+/// terminal error occurs.
+///
+/// Not implemented yet, currently always panics.
+pub async fn run_widget_api(
+    _room: JoinedRoom,
+    _widget: Widget,
+    _permissions_provider: impl PermissionsProvider,
+) -> Result<(), ()> {
+    todo!()
+}
diff --git a/crates/matrix-sdk/src/widget/permissions.rs b/crates/matrix-sdk/src/widget/permissions.rs
new file mode 100644
index 00000000000..9ebe1392676
--- /dev/null
+++ b/crates/matrix-sdk/src/widget/permissions.rs
@@ -0,0 +1,46 @@
+//! Types and traits related to the permissions that a widget can request from a
+//! client.
+
+use async_trait::async_trait;
+
+use crate::ruma::events::{MessageLikeEventType, StateEventType};
+
+/// Must be implemented by a component that provides functionality of deciding
+/// whether a widget is allowed to use certain capabilities (typically by
+/// providing a prompt to the user).
+#[async_trait]
+pub trait PermissionsProvider: Send + Sync + 'static {
+    /// Receives a request for given permissions and returns the actual
+    /// permissions that the clients grants to a given widget (usually by
+    /// prompting the user).
+    async fn acquire_permissions(&self, permissions: Permissions) -> Permissions;
+}
+
+/// Permissions that a widget can request from a client.
+#[derive(Debug)]
+pub struct Permissions {
+    /// Types of the messages that a widget wants to be able to fetch.
+    pub read: Vec<EventFilter>,
+    /// Types of the messages that a widget wants to be able to send.
+    pub send: Vec<EventFilter>,
+}
+
+/// Different kinds of filters that could be applied to the timeline events.
+#[derive(Debug)]
+pub enum EventFilter {
+    /// Message-like events.
+    MessageLike {
+        /// The type of the message-like event.
+        event_type: MessageLikeEventType,
+        /// Additional filter for the msgtype, currently only used for
+        /// `m.room.message`.
+        msgtype: Option<String>,
+    },
+    /// State events.
+    State {
+        /// The type of the state event.
+        event_type: StateEventType,
+        /// State key that could be `None`, `None` means "any state key".
+        state_key: Option<String>,
+    },
+}