diff --git a/src/main.rs b/src/main.rs
index 2d609ae..002fb34 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,5 +1,7 @@
 use clap::{Parser, Subcommand};
 
+use std::collections::HashSet;
+
 use std::fs;
 use std::io::{self, Write, BufRead};
 use std::path::Path;
@@ -9,6 +11,9 @@ const STORAGE_FOLDER: &str = "storage";
 const STORAGE_PATH: &str = "storage/db.mps"; // TODO: concat from STORAGE_FOLDER
 
 
+type DB = HashSet<String>;
+
+
 #[derive(Parser)]
 #[command(name = "mps", version = "0.0.1", about = "MyPasswordStorage: Tool for storing your passwords locally with git synchronization")]
 struct Cli {
@@ -33,6 +38,23 @@ enum Commands {
     
 }
 
+fn read_db() -> io::Result<DB> {
+    let file = fs::File::open(STORAGE_PATH)?;
+    let reader = io::BufReader::new(file);
+    let mut db = DB::new();
+    for line in reader.lines() {
+        match line {
+            Ok(content) => {
+                db.insert(content);
+            },
+            Err(e) => {
+                eprintln!("Error reading line , {}", e);
+            }
+        }
+    }
+    Ok(db)
+}
+
 fn is_inited() -> bool {
     let path = Path::new(STORAGE_FOLDER);
     return path.exists();
@@ -53,6 +75,14 @@ fn init() -> io::Result<()> {
 }
 
 fn add(id: &String) -> io::Result<()> {
+    let db = read_db()?;
+    if db.contains(id) {
+        // TODO: ask to edit existing in outer function which invoked this one
+        return Err(io::Error::new(
+            io::ErrorKind::InvalidInput,
+            format!("Dublicate item id: {}. Item id's must be unique.", id)
+        ))
+    }
     let mut file = fs::OpenOptions::new()
         .write(true)
         .append(true)
@@ -62,19 +92,10 @@ fn add(id: &String) -> io::Result<()> {
     Ok(())
 }
 
-// TODO: make this to return just set on values, will need later to check ids
 fn list() -> io:: Result<()> {
-    let file = fs::File::open(STORAGE_PATH)?;
-    let reader = io::BufReader::new(file);
-    for line in reader.lines() {
-        match line {
-            Ok(content) => {
-                println!("{}", content)
-            },
-            Err(e) => {
-                eprintln!("Error reading line , {}", e);
-            }
-        }
+    let db = read_db()?;
+    for item in db.iter() {
+        println!("{}", item);
     }
     Ok(())
 }