diff --git a/src/api/change.rs b/src/api/change.rs
new file mode 100644
index 0000000..e911fae
--- /dev/null
+++ b/src/api/change.rs
@@ -0,0 +1,56 @@
+//! # TextChange
+//! this represent a range in the previous state of the string and a new content which should be
+//! replaced to it, allowing to represent any combination of deletions, insertions or replacements
+//!
+//! bulk and widespread operations will result in a TextChange effectively sending the whole new
+//! buffer, but small changes are efficient and easy to create or apply 
+//!
+//! ### examples
+//! to insert 'a' after 4th character we should send a
+//!     `TextChange { span: 4..4, content: "a".into() }`
+//!
+//! to delete a the fourth character we should send a
+//!     `TextChange { span: 3..4, content: "".into() }`
+//!
+
+/// an editor-friendly representation of a text change in a buffer
+///  span refers to previous text content
+#[derive(Clone, Debug, Default)]
+pub struct TextChange {
+	/// range of text change, as char indexes in buffer previous state
+	pub span: std::ops::Range<usize>,
+	/// new content of text inside span
+	pub content: String,
+}
+
+impl TextChange {
+	/// create a new TextChange from the difference of given strings
+	pub fn from_diff(before: &str, after: &str) -> TextChange {
+		let diff = similar::TextDiff::from_chars(before, after);
+		let mut start = 0;
+		let mut end = 0;
+		let mut from_beginning = true;
+		for op in diff.ops() {
+			match op {
+				similar::DiffOp::Equal { .. } => {
+					if from_beginning {
+						start += 1
+					} else {
+						end += 1
+					}
+				},
+				_ => {
+					end = 0;
+					from_beginning = false;
+				}
+			}
+		}
+		let end_before = before.len() - end;
+		let end_after = after.len() - end;
+
+		TextChange {
+			span: start..end_before,
+			content: after[start..end_after].to_string(),
+		}
+	}
+}
diff --git a/src/api/mod.rs b/src/api/mod.rs
index 12a6070..fcb5f3e 100644
--- a/src/api/mod.rs
+++ b/src/api/mod.rs
@@ -7,4 +7,8 @@
 /// a generic async provider for bidirectional communication
 pub mod controller;
 
+/// a generic representation of a text change
+pub mod change;
+
 pub use controller::Controller;
+pub use change::TextChange;
diff --git a/src/buffer/controller.rs b/src/buffer/controller.rs
index fd44772..52f86e2 100644
--- a/src/buffer/controller.rs
+++ b/src/buffer/controller.rs
@@ -11,7 +11,7 @@ use tonic::async_trait;
 use crate::errors::IgnorableError;
 use crate::{api::Controller, Error};
 
-use super::TextChange;
+use crate::api::TextChange;
 
 /// the buffer controller implementation
 ///
diff --git a/src/buffer/mod.rs b/src/buffer/mod.rs
index 6dde13c..1610400 100644
--- a/src/buffer/mod.rs
+++ b/src/buffer/mod.rs
@@ -12,18 +12,3 @@ pub mod controller;
 pub(crate) mod worker;
 
 pub use controller::BufferController as Controller;
-
-
-/// an editor-friendly representation of a text change in a buffer
-///
-/// TODO move in proto
-#[derive(Clone, Debug, Default)]
-pub struct TextChange {
-	/// range of text change, as byte indexes in buffer
-	pub span: std::ops::Range<usize>,
-	/// content of text change, as string
-	pub content: String,
-	/// content after this text change
-	/// note that this field will probably be dropped, don't rely on it
-	pub after: String
-}
diff --git a/src/buffer/worker.rs b/src/buffer/worker.rs
index a8f7aa1..18e9510 100644
--- a/src/buffer/worker.rs
+++ b/src/buffer/worker.rs
@@ -12,8 +12,8 @@ use crate::errors::IgnorableError;
 use crate::proto::{OperationRequest, RawOp};
 use crate::proto::buffer_client::BufferClient;
 use crate::api::controller::ControllerWorker;
+use crate::api::TextChange;
 
-use super::TextChange;
 use super::controller::BufferController;
 
 
diff --git a/src/prelude.rs b/src/prelude.rs
index e49e505..4a147be 100644
--- a/src/prelude.rs
+++ b/src/prelude.rs
@@ -11,14 +11,16 @@ pub use crate::{
 pub use	crate::ot::OperationSeq as CodempOperationSeq;
 
 #[cfg(feature = "api")]
-pub use crate::api::Controller as CodempController;
+pub use crate::api::{
+	Controller as CodempController,
+	TextChange as CodempTextChange,
+};
 	
 #[cfg(feature = "client")]
 pub use crate::{
 	client::Client as CodempClient,
 	cursor::Controller as CodempCursorController,
 	buffer::Controller as CodempBufferController,
-	buffer::TextChange as CodempTextChange,
 	Instance as CodempInstance,
 };