diff --git a/Cargo.toml b/Cargo.toml
index e750b6c..3d04189 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -12,6 +12,7 @@ percent-encoding = "1.0.1"
 hyper = "0.12.10"
 log = "0.4.6"
 beautylog = "0.1.0"
+notify = "4.0.10"
 
 [[bin]]
 name = "mars-server"
diff --git a/src/lib.rs b/src/lib.rs
index 8e54835..08549d9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,7 +1,14 @@
-use std::io;
+#[macro_use]
+extern crate log;
+
+use std::{io, thread};
 use std::process::{Command, ExitStatus};
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 use std::fs::{File, create_dir_all};
+use std::sync::mpsc::channel;
+use std::time::Duration;
+
+use notify::{Watcher, RecursiveMode, DebouncedEvent, watcher};
 
 use notify_rust::Notification;
 
@@ -100,6 +107,29 @@ pub fn builder_arguments_from_string(uri: &str) -> (PathBuf, Vec<String>) {
     (path, args)
 }
 
+/// Watches a directory and builds it when a modification occurs.
+pub fn watch<P: AsRef<Path>>(p: P) -> Result<(), Error> {
+    let path = PathBuf::from(p.as_ref());
+    thread::spawn(move || {
+        let (tx, rx) = channel();
+        let mut watcher = watcher(tx, Duration::from_secs(10)).unwrap();
+        watcher.watch(&path, RecursiveMode::Recursive).unwrap();
+
+        loop {
+            match rx.recv() {
+                Ok(DebouncedEvent::NoticeWrite(_)) => {
+                    let builder = GeneralBuilder::new();
+                    builder.build(&path, &vec![]).ok();
+                },
+                Err(e) => error!("watch error: {:?}", e),
+                _ => (),
+            }
+        }
+    });
+
+    Ok(())
+}
+
 /// A general builders that contains many builders and can build any type of code.
 pub struct GeneralBuilder {
     /// The path to the success icon.
diff --git a/src/server.rs b/src/server.rs
index 32c7be1..19a8640 100644
--- a/src/server.rs
+++ b/src/server.rs
@@ -1,7 +1,7 @@
 #[macro_use]
 extern crate log;
 
-use std::thread;
+use std::{thread, env};
 use std::sync::{Mutex, Arc, mpsc};
 
 use colored::*;
@@ -12,12 +12,20 @@ use hyper::{Body, Response, Server};
 use hyper::service::service_fn_ok;
 use hyper::rt::Future;
 
-use mars::{GeneralBuilder, builder_arguments_from_string};
+use mars::{GeneralBuilder, builder_arguments_from_string, watch};
 
 fn main() {
 
     beautylog::init(log::LevelFilter::Info).ok();
 
+    let args = env::args().collect::<Vec<_>>();
+
+    if args.len() == 3 && args[1] == "-w" {
+        if let Err(e) = watch(&args[2]) {
+            error!("{:?}", e);
+        }
+    }
+
     let (tx, rx) = mpsc::channel();
 
     let tasks = Arc::new(Mutex::new(vec![]));