diff --git a/src/executors/mod.rs b/src/executors/mod.rs
index fdc8e75dc3..d977984bae 100644
--- a/src/executors/mod.rs
+++ b/src/executors/mod.rs
@@ -1 +1,26 @@
-pub trait Executor {}
+use crate::AflError;
+use crate::inputs::Input;
+use crate::observers::Observer;
+
+pub enum ExitKind {
+    Ok,
+    Crash,
+    OOM,
+    Timeout
+}
+
+pub trait Executor {
+
+    fn run_target(&mut self) -> Result<ExitKind, AflError>;
+
+    fn place_input(&mut self, entry: Box<dyn Input>) -> Result<(), AflError>;
+
+}
+
+// TODO abstract classes? how?
+pub struct ExecutorBase {
+
+    observers: Vec<Box<dyn Observer>>,
+    cur_input: Box<dyn Input>
+
+}
\ No newline at end of file
diff --git a/src/lib.rs b/src/lib.rs
index 9c6b412040..a8038b6d77 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -10,6 +10,7 @@ pub mod monitors;
 pub mod mutators;
 pub mod stages;
 pub mod utils;
+pub mod observers;
 
 #[derive(Error, Debug)]
 pub enum AflError {
diff --git a/src/observers/mod.rs b/src/observers/mod.rs
new file mode 100644
index 0000000000..22d8a103d7
--- /dev/null
+++ b/src/observers/mod.rs
@@ -0,0 +1,15 @@
+use crate::AflError;
+
+pub trait Observer {
+
+    fn flush(&mut self) -> Result<(), AflError> {
+        Ok(())
+    }
+
+    fn reset(&mut self) -> Result<(), AflError>;
+
+    fn post_exec(&mut self) -> Result<(), AflError> {
+        Ok(())
+    }
+
+}