diff --git a/cache-sync.wit b/cache-sync.wit
new file mode 100644
index 0000000..01e0d8e
--- /dev/null
+++ b/cache-sync.wit
@@ -0,0 +1,53 @@
+/// FastEdge cache interface (synchronous variant).
+interface cache-sync {
+  use cache-types.{payload, error};
+
+  /// Get the value associated with `key`.
+  ///
+  /// Returns:
+  /// - `ok(some(value))` if the key exists.
+  /// - `ok(none)` if the key does not exist.
+  /// - `err(error)` if the operation fails.
+  get: func(key: string) -> result<option<payload>, error>;
+
+  /// Set the value for `key` with an optional expiry.
+  ///
+  /// If the key already exists, its current value is overwritten.
+  /// If the key does not exist, a new key-value pair is created.
+  ///
+  /// `ttl-ms` is the time-to-live in milliseconds. Pass `none` for no expiry.
+  ///
+  /// Returns `err(error)` if the operation fails.
+  set: func(key: string, value: payload, ttl-ms: option<u64>) -> result<_, error>;
+
+  /// Delete the key-value pair associated with `key`.
+  ///
+  /// If the key does not exist, this operation is a no-op.
+  ///
+  /// Returns `err(error)` if the operation fails.
+  delete: func(key: string) -> result<_, error>;
+
+  /// Check whether `key` exists in the cache.
+  ///
+  /// Returns:
+  /// - `ok(true)` if the key exists.
+  /// - `ok(false)` if the key does not exist.
+  /// - `err(error)` if the operation fails.
+  exists: func(key: string) -> result<bool, error>;
+
+  /// Increment the integer value stored at `key` by `delta`.
+  ///
+  /// If the key does not exist, it is initialised to `0` before incrementing.
+  /// The operation is atomic. `delta` may be negative to decrement.
+  ///
+  /// Returns the new value after the increment, or `err(error)` if the
+  /// operation fails (for example, if the stored value is not an integer).
+  incr: func(key: string, delta: s64) -> result<s64, error>;
+
+  /// Set or update the expiry of `key` to `ttl-ms` milliseconds from now.
+  ///
+  /// If the key does not exist, returns `ok(false)`.
+  /// If the expiry was updated successfully, returns `ok(true)`.
+  /// Returns `err(error)` if the operation fails.
+  expire: func(key: string, ttl-ms: u64) -> result<bool, error>;
+}
diff --git a/cache-types.wit b/cache-types.wit
new file mode 100644
index 0000000..ea98bf8
--- /dev/null
+++ b/cache-types.wit
@@ -0,0 +1,15 @@
+/// Shared cache types for cache interfaces.
+interface cache-types {
+  type payload = list<u8>;
+
+  /// The set of errors that may be returned by cache operations.
+  variant error {
+    /// The requesting component does not have access to the specified cache
+    /// (which may or may not exist).
+    access-denied,
+    /// An unexpected internal error occurred.
+    internal-error,
+    /// An implementation-specific error occurred (for example, I/O).
+    other(string)
+  }
+}
diff --git a/world.wit b/world.wit
index 33587c9..f319593 100644
--- a/world.wit
+++ b/world.wit
@@ -7,6 +7,7 @@ world reactor {
     import secret;
     import key-value;
     import utils;
+    import cache-sync;
 
     export http-handler;
 }
\ No newline at end of file