diff --git a/Cargo.lock b/Cargo.lock
index 2baf233..7981f42 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,6 +2,243 @@
 # It is not intended for manual editing.
 version = 3
 
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+dependencies = [
+ "anstyle",
+ "anstyle-parse",
+ "anstyle-query",
+ "anstyle-wincon",
+ "colorchoice",
+ "is_terminal_polyfill",
+ "utf8parse",
+]
+
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+
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 [[package]]
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+ "windows_aarch64_msvc",
+ "windows_i686_gnu",
+ "windows_i686_gnullvm",
+ "windows_i686_msvc",
+ "windows_x86_64_gnu",
+ "windows_x86_64_gnullvm",
+ "windows_x86_64_msvc",
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diff --git a/Cargo.toml b/Cargo.toml
index b9957f2..fb16fe3 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,3 +6,8 @@ publish = false
 
 
 [dependencies]
+anyhow = "1.0"
+
+[dependencies.clap]
+version = "4.5"
+features = ["derive"]
diff --git a/src/dirs.rs b/src/dirs.rs
new file mode 100644
index 0000000..5c8c0be
--- /dev/null
+++ b/src/dirs.rs
@@ -0,0 +1,55 @@
+use std::fs;
+use std::path::PathBuf;
+use std::sync::OnceLock;
+
+use anyhow::Result;
+
+
+const APP_NAME: &str = env!("CARGO_PKG_NAME");
+const APP_ORG: &str = "valeth";
+
+static CONFIG: OnceLock<PathBuf> = OnceLock::new();
+static DATA: OnceLock<PathBuf> = OnceLock::new();
+static CACHE: OnceLock<PathBuf> = OnceLock::new();
+
+
+pub fn config_path() -> &'static PathBuf {
+    CONFIG.get_or_init(|| init("XDG_CONFIG_HOME", ".config").unwrap())
+}
+
+pub fn data_path() -> &'static PathBuf {
+    DATA.get_or_init(|| init("XDG_DATA_HOME", ".local/share").unwrap())
+}
+
+pub fn cache_path() -> &'static PathBuf {
+    CACHE.get_or_init(|| init("XDG_CACHE_HOME", ".cache").unwrap())
+}
+
+
+fn init(xdg_var: &str, fallback_home_path: &str) -> Result<PathBuf> {
+    let path = xdg_path_with_fallback(xdg_var, fallback_home_path)?;
+
+    if !path.exists() {
+        fs::create_dir_all(&path)?;
+    }
+
+    Ok(path)
+}
+
+
+fn xdg_path_with_fallback(xdg_var: &str, fallback_home_path: &str) -> Result<PathBuf> {
+    use std::env;
+
+    let user_home = env::var("HOME").expect("HOME variable is not set");
+    let user_home = PathBuf::from(user_home);
+
+    let apply_fallback = |e| match e {
+        env::VarError::NotPresent => Ok(user_home.join(fallback_home_path)),
+        _ => Err(e.into()),
+    };
+
+    env::var(xdg_var)
+        .map(PathBuf::from)
+        .or_else(apply_fallback)
+        .map(|path| path.join(APP_ORG).join(APP_NAME))
+}
diff --git a/src/main.rs b/src/main.rs
index 7527576..f21fce4 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,128 @@
-fn main() {
-    println!("hello");
+mod dirs;
+
+
+use std::ffi::OsStr;
+use std::fs;
+use std::io::{Read, Write};
+use std::path::PathBuf;
+
+use anyhow::{bail, ensure, Result};
+use clap::{Parser, Subcommand};
+
+
+#[derive(Debug, Parser)]
+pub struct Args {
+    #[command(subcommand)]
+    cmd: Command,
+}
+
+#[derive(Debug, Subcommand)]
+enum Command {
+    /// Add a project
+    Add { path: PathBuf },
+
+    /// List existing projects
+    List,
+}
+
+
+#[derive(Debug, Default)]
+struct Projects {
+    list: Vec<PathBuf>,
+}
+
+
+fn main() -> Result<()> {
+    let args = Args::parse();
+
+    let mut projects = read_projects_file()?;
+
+    let result = match &args.cmd {
+        Command::Add { path } => add_project(&mut projects, path),
+        Command::List => list_projects(&projects),
+    };
+
+    if let Err(err) = result {
+        eprintln!("{err}");
+        std::process::exit(1);
+    }
+
+    Ok(())
+}
+
+
+fn add_project<P>(projects: &mut Projects, path: P) -> Result<()>
+where
+    P: Into<PathBuf>,
+{
+    let path = path.into();
+
+    ensure!(path.is_dir(), "Project path does not exists");
+    ensure!(
+        !projects.list.contains(&path.to_path_buf()),
+        "Project path already registered"
+    );
+
+    projects.list.push(path);
+    write_projects_file(projects)?;
+
+    Ok(())
+}
+
+
+fn list_projects(projects: &Projects) -> Result<()> {
+    for project in &projects.list {
+        println!("{project:?}")
+    }
+
+    Ok(())
+}
+
+fn write_projects_file(projects: &Projects) -> Result<()> {
+    let projects_file = dirs::data_path().join("projects");
+
+    let mut file = fs::OpenOptions::new()
+        .write(true)
+        .create(true)
+        .truncate(true)
+        .open(projects_file)?;
+
+    for project_path in &projects.list {
+        let os_str = project_path.as_os_str();
+        let bytes = os_str.as_encoded_bytes();
+        file.write_all(bytes)?;
+        file.write_all(b"\n")?;
+    }
+
+    Ok(())
+}
+
+
+fn read_projects_file() -> Result<Projects> {
+    let projects_file = dirs::data_path().join("projects");
+
+    if !projects_file.exists() {
+        return Ok(Projects::default());
+    }
+
+    let mut file = std::fs::File::open(projects_file)?;
+
+    let mut buf = Vec::new();
+    file.read_to_end(&mut buf)?;
+
+
+    let list = buf
+        .split(|&x| x == b'\n')
+        .filter_map(|chunk| {
+            // FIXME: not a good idea to store the OsStr
+            let os_str = unsafe { OsStr::from_encoded_bytes_unchecked(chunk) };
+            if os_str.is_empty() {
+                None
+            } else {
+                Some(PathBuf::from(os_str))
+            }
+        })
+        .collect();
+
+    Ok(Projects { list })
 }