diff --git a/crates/core/src/bookmark.rs b/crates/core/src/bookmark.rs
new file mode 100644
index 0000000..0d36e3f
--- /dev/null
+++ b/crates/core/src/bookmark.rs
@@ -0,0 +1 @@
+pub struct BookmarkManager {/* TODO */}
diff --git a/crates/core/src/config.rs b/crates/core/src/config.rs
new file mode 100644
index 0000000..91554aa
--- /dev/null
+++ b/crates/core/src/config.rs
@@ -0,0 +1 @@
+pub struct AppConfig {/* TODO */}
diff --git a/crates/core/src/filter.rs b/crates/core/src/filter.rs
new file mode 100644
index 0000000..5bb720b
--- /dev/null
+++ b/crates/core/src/filter.rs
@@ -0,0 +1 @@
+pub struct Filter {/* TODO */}
diff --git a/crates/core/src/io/file_reader.rs b/crates/core/src/io/file_reader.rs
new file mode 100644
index 0000000..936af7a
--- /dev/null
+++ b/crates/core/src/io/file_reader.rs
@@ -0,0 +1,13 @@
+use crate::error::Result;
+use std::path::Path;
+
+pub struct FileReader {/* TODO */}
+
+impl FileReader {
+    pub fn open(_path: &Path) -> Result<Self> {
+        todo!()
+    }
+    pub fn file_size(&self) -> u64 {
+        todo!()
+    }
+}
diff --git a/crates/core/src/io/line_index.rs b/crates/core/src/io/line_index.rs
new file mode 100644
index 0000000..099a1e8
--- /dev/null
+++ b/crates/core/src/io/line_index.rs
@@ -0,0 +1 @@
+pub struct LineIndex {/* TODO */}
diff --git a/crates/core/src/io/mod.rs b/crates/core/src/io/mod.rs
new file mode 100644
index 0000000..6a2009d
--- /dev/null
+++ b/crates/core/src/io/mod.rs
@@ -0,0 +1,2 @@
+pub mod file_reader;
+pub mod line_index;
diff --git a/crates/core/src/lib.rs b/crates/core/src/lib.rs
index c8c9f1a..e7f0bfc 100644
--- a/crates/core/src/lib.rs
+++ b/crates/core/src/lib.rs
@@ -1,10 +1,10 @@
+pub mod bookmark;
+pub mod config;
 pub mod error;
+pub mod filter;
+pub mod io;
+pub mod parser;
+pub mod search;
+pub mod session;
 pub mod types;
-// pub mod io; — Task 4
-// pub mod search; — Task 4
-// pub mod parser; — Task 4
-// pub mod watcher; — Task 4
-// pub mod filter; — Task 4
-// pub mod bookmark; — Task 4
-// pub mod config; — Task 4
-// pub mod session; — Task 4
+pub mod watcher;
diff --git a/crates/core/src/parser/json.rs b/crates/core/src/parser/json.rs
new file mode 100644
index 0000000..25d05d0
--- /dev/null
+++ b/crates/core/src/parser/json.rs
@@ -0,0 +1,8 @@
+use crate::types::LogEntry;
+
+pub fn parse_line(_line: &str) -> Option<LogEntry> {
+    todo!()
+}
+pub fn detect_json_log(_line: &str) -> bool {
+    todo!()
+}
diff --git a/crates/core/src/parser/mod.rs b/crates/core/src/parser/mod.rs
new file mode 100644
index 0000000..22fdbb3
--- /dev/null
+++ b/crates/core/src/parser/mod.rs
@@ -0,0 +1 @@
+pub mod json;
diff --git a/crates/core/src/search/engine.rs b/crates/core/src/search/engine.rs
new file mode 100644
index 0000000..fd35e0d
--- /dev/null
+++ b/crates/core/src/search/engine.rs
@@ -0,0 +1 @@
+pub struct SearchEngine {/* TODO */}
diff --git a/crates/core/src/search/mod.rs b/crates/core/src/search/mod.rs
new file mode 100644
index 0000000..702e611
--- /dev/null
+++ b/crates/core/src/search/mod.rs
@@ -0,0 +1 @@
+pub mod engine;
diff --git a/crates/core/src/session.rs b/crates/core/src/session.rs
new file mode 100644
index 0000000..ce0e808
--- /dev/null
+++ b/crates/core/src/session.rs
@@ -0,0 +1 @@
+pub struct SessionManager {/* TODO */}
diff --git a/crates/core/src/watcher/file_watcher.rs b/crates/core/src/watcher/file_watcher.rs
new file mode 100644
index 0000000..001a391
--- /dev/null
+++ b/crates/core/src/watcher/file_watcher.rs
@@ -0,0 +1,2 @@
+pub struct FileWatcher {/* TODO */}
+pub struct SmartFollow {/* TODO */}
diff --git a/crates/core/src/watcher/mod.rs b/crates/core/src/watcher/mod.rs
new file mode 100644
index 0000000..d19e065
--- /dev/null
+++ b/crates/core/src/watcher/mod.rs
@@ -0,0 +1 @@
+pub mod file_watcher;