diff --git a/Cargo.toml b/Cargo.toml
index eefa32a..d1637fb 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,3 +1,6 @@
+[workspace]
+members = [".", "crates/*"]
+
 [package]
 authors = ["Takahiro Sato <harehare1110@gmail.com>"]
 categories = ["command-line-utilities", "text-processing"]
diff --git a/crates/mq-desktop/Cargo.toml b/crates/mq-desktop/Cargo.toml
new file mode 100644
index 0000000..0e1c282
--- /dev/null
+++ b/crates/mq-desktop/Cargo.toml
@@ -0,0 +1,14 @@
+[package]
+name = "mq-desktop"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+eframe = "0.31.0"
+egui_commonmark = { version = "0.20.0", features = ["better_syntax_highlighting", "svg", "fetch"] }
+mq-lang = "0.5.19"
+mq-markdown = "0.5.19"
+notify = "8.2.0"
+syntect = "5.3.0"
+clap = { version = "4.5.21", features = ["derive"] }
+anyhow = "1.0.93"
diff --git a/crates/mq-desktop/src/main.rs b/crates/mq-desktop/src/main.rs
new file mode 100644
index 0000000..3c6c6ad
--- /dev/null
+++ b/crates/mq-desktop/src/main.rs
@@ -0,0 +1,322 @@
+use anyhow::Result;
+use clap::Parser;
+use eframe::egui;
+use egui_commonmark::{CommonMarkCache, CommonMarkViewer};
+use notify::{Watcher, RecursiveMode};
+use std::path::PathBuf;
+use std::sync::mpsc::{channel, Receiver};
+use std::fs;
+use std::time::{Duration, Instant};
+use mq_markdown::Markdown;
+
+const COLOR_BRAND_BLUE: egui::Color32 = egui::Color32::from_rgb(97, 175, 239); // #61AFEF
+const _COLOR_BRAND_DARK: egui::Color32 = egui::Color32::from_rgb(43, 87, 115);  // #2B5773
+
+#[derive(Parser, Debug)]
+#[command(author, version, about, long_about = None)]
+struct Args {
+    /// Markdown file to preview
+    file: Option<PathBuf>,
+}
+
+fn main() -> Result<()> {
+    let args = Args::parse();
+
+    let options = eframe::NativeOptions {
+        viewport: egui::ViewportBuilder::default()
+            .with_inner_size([1280.0, 720.0])
+            .with_title("MQ Desktop"),
+        ..Default::default()
+    };
+
+    eframe::run_native(
+        "MQ Desktop",
+        options,
+        Box::new(|cc| {
+            let mut app = MQApp::new(cc, args.file);
+            app.load_file();
+            Ok(Box::new(app))
+        }),
+    ).map_err(|e| anyhow::anyhow!("eframe error: {}", e))
+}
+
+struct TocEntry {
+    level: u32,
+    text: String,
+}
+
+#[derive(PartialEq)]
+enum ViewMode {
+    Original,
+    QueryResult,
+}
+
+struct MQApp {
+    file_path: Option<PathBuf>,
+    markdown_content: String,
+    query: String,
+    query_result: Option<String>,
+    toc: Vec<TocEntry>,
+    cache: CommonMarkCache,
+    rx: Option<Receiver<notify::Result<notify::Event>>>,
+    _watcher: Option<notify::RecommendedWatcher>,
+    last_query_change: Option<Instant>,
+    view_mode: ViewMode,
+    dark_mode: bool,
+}
+
+impl MQApp {
+    fn new(cc: &eframe::CreationContext<'_>, file_path: Option<PathBuf>) -> Self {
+        let (tx, rx) = channel();
+        let mut watcher = None;
+        let ctx = cc.egui_ctx.clone();
+
+        if let Some(ref path) = file_path {
+            let mut w = notify::recommended_watcher(move |res| {
+                if tx.send(res).is_ok() {
+                    ctx.request_repaint();
+                }
+            }).expect("Failed to create watcher");
+            w.watch(path, RecursiveMode::NonRecursive).expect("Failed to watch file");
+            watcher = Some(w);
+        }
+
+        Self {
+            file_path,
+            markdown_content: String::new(),
+            query: "select *".to_string(),
+            query_result: None,
+            toc: Vec::new(),
+            cache: CommonMarkCache::default(),
+            rx: Some(rx),
+            _watcher: watcher,
+            last_query_change: None,
+            view_mode: ViewMode::QueryResult,
+            dark_mode: true,
+        }
+    }
+
+    fn load_file(&mut self) {
+        if let Some(ref path) = self.file_path {
+            if let Ok(content) = fs::read_to_string(path) {
+                self.markdown_content = content;
+                self.update_toc();
+                self.run_query();
+            }
+        }
+    }
+
+    fn update_toc(&mut self) {
+        let mut toc = Vec::new();
+        if let Ok(markdown) = self.markdown_content.parse::<Markdown>() {
+            for node in &markdown.nodes {
+                self.extract_headings(node, &mut toc);
+            }
+        }
+        self.toc = toc;
+    }
+
+    fn extract_headings(&self, node: &mq_markdown::Node, toc: &mut Vec<TocEntry>) {
+        use mq_markdown::Node;
+        match node {
+            Node::Heading(h) => {
+                let mut text = String::new();
+                for child in &h.values {
+                    self.extract_text(child, &mut text);
+                }
+                toc.push(TocEntry {
+                    level: h.depth as u32,
+                    text,
+                });
+            }
+            Node::Blockquote(b) => {
+                for child in &b.values {
+                    self.extract_headings(child, toc);
+                }
+            }
+            Node::List(l) => {
+                for child in &l.values {
+                    self.extract_headings(child, toc);
+                }
+            }
+            _ => {}
+        }
+    }
+
+    fn extract_text(&self, node: &mq_markdown::Node, text: &mut String) {
+        use mq_markdown::Node;
+        match node {
+            Node::Text(t) => text.push_str(&t.value),
+            Node::CodeInline(c) => text.push_str(&c.value),
+            Node::Emphasis(e) => {
+                for child in &e.values {
+                    self.extract_text(child, text);
+                }
+            }
+            Node::Strong(s) => {
+                for child in &s.values {
+                    self.extract_text(child, text);
+                }
+            }
+            Node::Delete(d) => {
+                for child in &d.values {
+                    self.extract_text(child, text);
+                }
+            }
+            _ => {}
+        }
+    }
+
+    fn run_query(&mut self) {
+        let mut engine = mq_lang::DefaultEngine::default();
+        engine.load_builtin_module();
+
+        let input = mq_lang::parse_markdown_input(&self.markdown_content);
+
+        match input {
+            Ok(input_values) => {
+                match engine.eval(&self.query, input_values.into_iter()) {
+                    Ok(results) => {
+                        if results.is_empty() {
+                            self.query_result = Some("No results found.".to_string());
+                        } else {
+                            let result_strings: Vec<String> = results.into_iter().map(|v| {
+                                match v {
+                                    mq_lang::RuntimeValue::Markdown(node, _) => node.to_string(),
+                                    mq_lang::RuntimeValue::String(s) => s,
+                                    _ => format!("{:?}", v),
+                                }
+                            }).collect();
+                            self.query_result = Some(result_strings.join("\n\n"));
+                        }
+                    }
+                    Err(e) => {
+                        self.query_result = Some(format!("Query Error: {}", e));
+                    }
+                }
+            }
+            Err(e) => {
+                self.query_result = Some(format!("Parse Error: {}", e));
+            }
+        }
+    }
+
+    fn apply_styling(&self, ctx: &egui::Context) {
+        if self.dark_mode {
+            ctx.set_visuals(egui::Visuals::dark());
+        } else {
+            ctx.set_visuals(egui::Visuals::light());
+        }
+    }
+}
+
+impl eframe::App for MQApp {
+    fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
+        self.apply_styling(ctx);
+
+        let mut should_reload = false;
+        if let Some(ref rx) = self.rx {
+            while let Ok(_) = rx.try_recv() {
+                should_reload = true;
+            }
+        }
+        if should_reload {
+            self.load_file();
+        }
+
+        if let Some(last_change) = self.last_query_change {
+            if last_change.elapsed() >= Duration::from_millis(300) {
+                self.run_query();
+                self.last_query_change = None;
+            } else {
+                ctx.request_repaint_after(Duration::from_millis(100));
+            }
+        }
+
+        egui::SidePanel::left("toc_panel")
+            .resizable(true)
+            .default_width(250.0)
+            .show(ctx, |ui| {
+                ui.add_space(10.0);
+                ui.heading(egui::RichText::new("Contents").color(COLOR_BRAND_BLUE));
+                ui.separator();
+                egui::ScrollArea::vertical().show(ui, |ui| {
+                    for entry in &self.toc {
+                        let indent = (entry.level as f32 - 1.0) * 12.0;
+                        ui.add_space(4.0);
+                        ui.horizontal(|ui| {
+                            ui.add_space(indent);
+                            if ui.selectable_label(false, &entry.text).clicked() {
+                                // Scroll logic would go here
+                            }
+                        });
+                    }
+                });
+            });
+
+        egui::TopBottomPanel::top("header_panel").show(ctx, |ui| {
+            ui.horizontal(|ui| {
+                ui.heading(egui::RichText::new("mq").strong().color(COLOR_BRAND_BLUE));
+                ui.label("desktop");
+
+                ui.with_layout(egui::Layout::right_to_left(egui::Align::Center), |ui| {
+                    if ui.button(if self.dark_mode { "🌙" } else { "☀️" }).clicked() {
+                        self.dark_mode = !self.dark_mode;
+                    }
+                    ui.separator();
+                    if let Some(ref path) = self.file_path {
+                        ui.label(egui::RichText::new(path.to_string_lossy()).small());
+                    }
+                });
+            });
+        });
+
+        egui::TopBottomPanel::top("query_panel").show(ctx, |ui| {
+            ui.add_space(5.0);
+            ui.vertical(|ui| {
+                ui.horizontal(|ui| {
+                    ui.label(egui::RichText::new("Query").strong());
+                    let response = ui.add(
+                        egui::TextEdit::singleline(&mut self.query)
+                            .desired_width(f32::INFINITY)
+                            .hint_text("e.g. select * where .h2")
+                    );
+                    if response.changed() {
+                        self.last_query_change = Some(Instant::now());
+                    }
+                });
+
+                ui.horizontal(|ui| {
+                    ui.selectable_value(&mut self.view_mode, ViewMode::QueryResult, "Query Result");
+                    ui.selectable_value(&mut self.view_mode, ViewMode::Original, "Original Preview");
+
+                    ui.with_layout(egui::Layout::right_to_left(egui::Align::Center), |ui| {
+                        let button = egui::Button::new(egui::RichText::new("Run").color(egui::Color32::WHITE))
+                            .fill(COLOR_BRAND_BLUE);
+                        if ui.add(button).clicked() {
+                            self.run_query();
+                            self.last_query_change = None;
+                        }
+                    });
+                });
+            });
+            ui.add_space(5.0);
+        });
+
+        egui::CentralPanel::default().show(ctx, |ui| {
+            egui::ScrollArea::vertical().show(ui, |ui| {
+                let display_content = match self.view_mode {
+                    ViewMode::QueryResult => self.query_result.as_deref().unwrap_or("No query results yet."),
+                    ViewMode::Original => &self.markdown_content,
+                };
+                if display_content.is_empty() {
+                    ui.centered_and_justified(|ui| {
+                        ui.label("No content to display.");
+                    });
+                } else {
+                    CommonMarkViewer::new().show(ui, &mut self.cache, display_content);
+                }
+            });
+        });
+    }
+}