diff --git a/src/core.rs b/src/core.rs
index 131c312..54f9a82 100644
--- a/src/core.rs
+++ b/src/core.rs
@@ -14,7 +14,9 @@ use std::fs::File;
 pub struct XContext {
     pub conn: RustConnection,
     pub root: u32,
+    #[allow(dead_code)]
     pub width: u16,
+    #[allow(dead_code)]
     pub height: u16,
 }
 
@@ -46,28 +48,36 @@ impl XContext {
     }
 }
 
-/// Capture a rectangular part of the screen.
+/// Capture a rectangular part of the screen.  
 ///
-/// `ctx`  – connection + screen info  
-/// `x,y` – top-left corner of the rectangle  
+/// `ctxt`  – connection + screen info\
+/// `x_coord,y_coord` – top-left corner of the rectangle\
 /// `w,h` – size of the rectangle  
 ///
 /// Returns: a `Vec<u8>` containing RGBA pixel data.
-pub fn capture_rect(ctx: &XContext, x: u16, y: u16, w: u16, h: u16) -> anyhow::Result<Vec<u8>> {
+pub fn capture_rect(
+    ctxt: &XContext,
+    top_left_x: u16,
+    top_left_y: u16,
+    width: u16,
+    height: u16,
+) -> anyhow::Result<Vec<u8>> {
     // X11 uses the number 2 for "ZPixmap", which means: return full pixel data.
     let format_zpixmap: u8 = 2;
+    let x_coord = i16::try_from(top_left_x).unwrap_or(0);
+    let y_coord = i16::try_from(top_left_y).unwrap_or(0);
 
     // Ask X11 to send us the raw pixels in the requested rectangle.
     // This returns X11's native pixel format (usually B,G,R,unused).
-    let reply = ctx
+    let reply = ctxt
         .conn
         .get_image(
             format_zpixmap.into(),
-            ctx.root,
-            x as i16,
-            y as i16,
-            w,
-            h,
+            ctxt.root,
+            x_coord,
+            y_coord,
+            width,
+            height,
             u32::MAX,
         )?
         .reply()?;
@@ -76,7 +86,7 @@ pub fn capture_rect(ctx: &XContext, x: u16, y: u16, w: u16, h: u16) -> anyhow::R
 
     // Prepare a buffer for RGBA output.
     // Each pixel = 4 bytes (R, G, B, A).
-    let mut out = Vec::with_capacity((w as usize) * (h as usize) * 4);
+    let mut out = Vec::with_capacity((width as usize) * (height as usize) * 4);
 
     // Convert each incoming pixel from X11's format (B, G, R, X)
     // into the common RGBA format that PNG expects.
@@ -92,11 +102,11 @@ pub fn capture_rect(ctx: &XContext, x: u16, y: u16, w: u16, h: u16) -> anyhow::R
     Ok(out)
 }
 
-/// Save an RGBA pixel buffer as a PNG file.
+/// Save an RGBA pixel buffer as a PNG file.  
 ///
-/// `path`   – where to write the file  
-/// `width`  – image width in pixels  
-/// `height` – image height in pixels  
+/// `path`   – where to write the file\
+/// `width`  – image width in pixels\
+/// `height` – image height in pixels\
 /// `rgba`   – pixel data in RGBA format  
 pub fn save_png(path: &str, width: u16, height: u16, rgba: &[u8]) -> anyhow::Result<()> {
     let file = File::create(path)?;
diff --git a/src/window.rs b/src/window.rs
index 244f744..18c3193 100644
--- a/src/window.rs
+++ b/src/window.rs
@@ -1,3 +1,79 @@
-fn main() {
-    println!("Hello");
+mod core;
+
+use core::{XContext, capture_rect, save_png};
+
+use chrono::Local;
+use std::fs;
+use x11rb::protocol::xproto::{AtomEnum, ConnectionExt, GetGeometryReply, Window};
+
+fn main() -> anyhow::Result<()> {
+    // Connect to X11 and load screen info.
+    let ctx = XContext::new()?;
+
+    // Try to get the currently active window using EWMH (_NET_ACTIVE_WINDOW).
+    let window = get_active_window(&ctx).unwrap_or_else(|| {
+        eprintln!("Could not get active window. Falling back to input focus.");
+        get_focused_window(&ctx).unwrap_or(ctx.root)
+    });
+
+    // Read the size and position of that window.
+    let geom = get_window_geometry(&ctx, window)?;
+
+    let x = u16::try_from(geom.x.max(0)).unwrap();
+    let y = u16::try_from(geom.y.max(0)).unwrap();
+
+    // Capture only the window rectangle.
+    let img = capture_rect(&ctx, x, y, geom.width, geom.height)?;
+
+    // Build output path: ~/Pictures/Screenshots/window_TIMESTAMP.png
+    let timestamp = Local::now().format("%Y%m%d%H%M%S").to_string();
+
+    let mut path = dirs::home_dir().unwrap_or_else(|| ".".into());
+    path.push("Pictures");
+    path.push("Screenshots");
+    fs::create_dir_all(&path)?;
+    path.push(format!("window_{timestamp}.png"));
+
+    let path_str = path.to_string_lossy();
+    save_png(&path_str, geom.width, geom.height, &img)?;
+
+    println!("Saved {path_str}");
+
+    Ok(())
+}
+
+/// Ask the window manager for the active window using the EWMH protocol.
+///
+/// This works on most modern Linux desktops.
+/// Returns None if the WM does not support this.
+fn get_active_window(ctx: &XContext) -> Option<Window> {
+    let atom = ctx
+        .conn
+        .intern_atom(false, b"_NET_ACTIVE_WINDOW")
+        .ok()?
+        .reply()
+        .ok()?
+        .atom;
+
+    let reply = ctx
+        .conn
+        .get_property(false, ctx.root, atom, AtomEnum::WINDOW, 0, 1)
+        .ok()?
+        .reply()
+        .ok()?;
+
+    // The active window ID is stored as a 32-bit value.
+    reply.value32().and_then(|mut iter| iter.next())
+}
+
+/// Fallback method: get the window that currently has keyboard focus.
+fn get_focused_window(ctx: &XContext) -> Option<Window> {
+    let reply = ctx.conn.get_input_focus().ok()?.reply().ok()?;
+    Some(reply.focus)
+}
+
+/// Read x, y, width, height of a window.
+fn get_window_geometry(ctx: &XContext, win: Window) -> anyhow::Result<GetGeometryReply> {
+    let geom = ctx.conn.get_geometry(win)?.reply()?;
+    Ok(geom)
 }