diff --git a/lib/commandLineParser.cpp b/lib/commandLineParser.cpp
index 2e70cca..779e90c 100644
--- a/lib/commandLineParser.cpp
+++ b/lib/commandLineParser.cpp
@@ -1,25 +1,64 @@
 #include "commandLineParser.h"
 #include <iostream>
+#include <stdexcept> // for std::invalid_argument
 
+//implement hashmap for the code
 CLI::CLI(int argc, char** argv){
-    if (argc > 0){
+    try{
+        if (arc < 2) {
+            throw std::invalid_argument("Error: No input file provided.\n
+                                         Usage: <program> <input_file>");
+        }
+        //sets program info
         programName = argv[0];
+        inputFile = argv[1]
+
+        //checks that file has correct file extension
+        if(!(CLI::IsMarkupFile(inputFile))) {
+            throw std::invalid_argument("Error: Invalid file extension. Expected a '.md' (Markdown) file.");
+        }
+        //stores remaining arguments
+        for (int i = 1; i < argc; i++){
+            args.push_back(argv[i]);
+        }
+        }
+    catch (const std::invalid_argument& e) {
+        std::cerr << e.what() << "\n";
+        PrintHelp();
+        std::exit(EXIT_FAILURE);
+    }
     }
 
-    for (int i = 1; i < argc; i++){
-        args.push_back(argv[i]);
+bool CLI::IsMarkupFile(const std::string& filename) {
+    //markdown file extension
+    const std::string requiredExtension = ".md";
+    //checks to see if it can even include extension
+    if (filename.size() <= requiredExtension.size()) {
+        return false;
     }
+    // Extracts the last N characters of the filename (where N is the length of the required extension)
+    // and checks if they match the required file extension (e.g., ".md").
+    //
+    // Example:
+    //   filename = "notes.md"
+    //   requiredExtension = ".md"
+    //   filename.substr(filename.size() - requiredExtension.size()) == ".md" → true
+    //
+    // Reference: https://en.cppreference.com/w/cpp/string/basic_string/substr
+    return filename.substr(filename.size() - requiredExtension.size()) == requiredExtension;
 }
 
+
+//place to run commands but IDK IF WE SHOULD USE A HASMAP or how we are going to get each method to run
 void CLI::RunCommands(){
     for (int i = 0; i < args.size(); i++){
-        
+
     }    
 }
 
 void CLI::PrintHelp() const{
     std::cout << "Usage:\n"
-              << " " << programName << " <input_file>\n"
+              << " " << programName << " <input_file> REQUIRED\n"
               << "Flags:\n"
               << " --o, --output <outputFile>, optional output filename\n"
               << " --w, --watch, enables watchdog\n"
diff --git a/lib/commandLineParser.h b/lib/commandLineParser.h
index 5d595bc..88c9a09 100644
--- a/lib/commandLineParser.h
+++ b/lib/commandLineParser.h
@@ -60,6 +60,17 @@ public:
     std::string GetOutputFile() const {return outputFile;}
 
 private:
+
+    /**
+     * @brief Ensures the provided filename has a .markup extension
+     *
+     * @param filename The file name to validate
+     * @return true if file ends with .markup
+     * @return false otherwise
+     * @author Preston Shultz (shultzp1@my.erau.edu)
+     */
+    static bool IsMarkupFile(const std::string& filename);
+    
     std::string programName;
     std::vector<std::string> args;
     std::string inputFile;
diff --git a/lib/watchDog.cpp b/lib/watchDog.cpp
index 0b0284c..5894935 100644
--- a/lib/watchDog.cpp
+++ b/lib/watchDog.cpp
@@ -1,63 +1,77 @@
 #include "watchdog.h"
 
 namespace fs = std::filesystem; //makes it easier to read
-
-void Watchdog::Start()
+void WatchDog::start()
 {
-    //Checks if file exist
+    //checks if file exist
     if(!fs::exists(path))
     {
-        //Returns and sets parameters to false if file doesnt exist
+        //returns and sets parameters to false if file doesnt exist
         watching = false;
-        has_initial_time = false;
+        hasInitialTime = false;
         std::cout << "WatchDog: File does not exists: " << path << std::endl;
         return;
     }
-    //Grabs intial write time
-    last_write_time = fs::last_write_time(path);
-    //Sets watchdog
+    //grabs intial write time
+    lastWriteTime = fs::last_write_time(path);
     watching = true;
-    has_initial_time = true;
+    hasInitialTime = true;
     std::cout << "WatchDog: Started" << std::endl;
 }
-
-bool Watchdog::CheckFile(){
+void WatchDog::stop(){
+    watching = false;
+}
+bool WatchDog::checkFile(){
     //If not watching returns false
     if (!watching) return false;
 
     //Checking if file was deleted
     if(!fs::exists(path))
     {
-        if (has_initial_time) {
+        if (hasInitialTime) {
             std::cout << "WatchDog: File was delete: " << path << std::endl;
-            has_initial_time = false;
+            hasInitialTime = false;
             return true;
         }
         return false;
     }
     
-    //Built in function with file system to check last write time
+    //Built in function with file system to check last write tim
     fs::file_time_type currentWriteTime = fs::last_write_time(path);
 
     //File was just created
-    if(!has_initial_time)
+    if(!hasInitialTime)
     {
-        last_write_time = currentWriteTime;
-        has_initial_time = true;
+        lastWriteTime = currentWriteTime;
+        hasInitialTime = true;
         std::cout << "WatchDog: File created: " << path << std::endl;
         return true;
     }
 
     //File modified
-    if (currentWriteTime != last_write_time)
+    if (currentWriteTime != lastWriteTime)
     {
-        last_write_time = currentWriteTime;
+        lastWriteTime = currentWriteTime;
         std::cout << "WatchDog: File modifed at " 
-                  << TimePointToString(last_write_time) << std::endl;
+                  << timePointToString(lastWriteTime) << std::endl;
         return true;      
     }
 
-    //No change
+    } catch (const fs::filesystem_error& e) {
+        // File deleted, inaccessible, or path invalid
+        if (hasInitialTime) {
+            std::cout << "WatchDog: File deleted or inaccessible: " << path << std::endl;
+            hasInitialTime = false;
+            return true;
+        }
+        return false;
+
+    } catch (const std::exception& e) {
+        std::cerr << "WatchDog: Unexpected error checking file: " << e.what() << std::endl;
+        return false;
+    }
+
+    // No change
     return false;
 }