diff --git a/src/FileSystem.php b/src/FileSystem.php
index 2c55272..c137425 100644
--- a/src/FileSystem.php
+++ b/src/FileSystem.php
@@ -10,8 +10,17 @@ use PmConverter\Exceptions\{
     DirectoryIsNotWriteableException,
     DirectoryNotExistsException};
 
+/**
+ * Helper class to work with files and directories
+ */
 class FileSystem
 {
+    /**
+     * Normalizes a given path
+     *
+     * @param string $path
+     * @return string
+     */
     public static function normalizePath(string $path): string
     {
         $path = str_replace('~', $_SERVER['HOME'], $path);
@@ -19,6 +28,8 @@ class FileSystem
     }
 
     /**
+     * Recursively creates a new directory by given path
+     *
      * @param string $path
      * @return string
      * @throws CannotCreateDirectoryException
@@ -38,6 +49,8 @@ class FileSystem
     }
 
     /**
+     * Recursively removes a given directory
+     *
      * @param string $path
      * @return void
      * @throws DirectoryIsNotReadableException
@@ -77,11 +90,10 @@ class FileSystem
     }
 
     /**
+     * Returns content of given directory path
+     *
      * @param string $path
      * @return array
-     * @throws DirectoryIsNotReadableException
-     * @throws DirectoryIsNotWriteableException
-     * @throws DirectoryNotExistsException
      */
     public static function dirContents(string $path): array
     {
@@ -92,4 +104,22 @@ class FileSystem
         }
         return $records;
     }
+
+    /**
+     * Checks if a given file is a valid collection json file
+     *
+     * @param string $path
+     * @return bool
+     */
+    public static function isCollectionFile(string $path): bool
+    {
+        $path = static::normalizePath($path);
+        return !empty($path = trim($path))
+            && str_ends_with($path, '.postman_collection.json')
+            && file_exists($path)
+            && is_readable($path)
+            && ($json = json_decode(file_get_contents($path), true))
+            && json_last_error() === JSON_ERROR_NONE
+            && isset($json['collection']['info']['name']);
+    }
 }
diff --git a/src/Processor.php b/src/Processor.php
index 945c434..382296e 100644
--- a/src/Processor.php
+++ b/src/Processor.php
@@ -92,47 +92,58 @@ class Processor
             switch ($arg) {
                 case '-f':
                 case '--file':
-                    $path = FileSystem::normalizePath($this->argv[$idx + 1]);
-                    if (empty($path) || !str_ends_with($path, '.json') || !file_exists($path) || !is_readable($path)) {
-                        throw new InvalidArgumentException('a valid json-file path is expected for -f (--file)');
+                    $rawpath = $this->argv[$idx + 1];
+                    $normpath = FileSystem::normalizePath($rawpath);
+                    if (!FileSystem::isCollectionFile($normpath)) {
+                        throw new InvalidArgumentException(
+                            sprintf("this is not a valid collection file:%s\t%s %s", PHP_EOL, $arg, $rawpath)
+                        );
                     }
                     $this->collectionPaths[] = $this->argv[$idx + 1];
                     break;
+
                 case '-o':
                 case '--output':
                     if (empty($this->argv[$idx + 1])) {
-                        throw new InvalidArgumentException('-o expected');
+                        throw new InvalidArgumentException('-o is required');
                     }
                     $this->outputPath = $this->argv[$idx + 1];
                     break;
+
                 case '-d':
                 case '--dir':
                     if (empty($this->argv[$idx + 1])) {
                         throw new InvalidArgumentException('a directory path is expected for -d (--dir)');
                     }
-                    $path = $this->argv[$idx + 1];
+                    $normpath = $this->argv[$idx + 1];
                     $files = array_filter(
-                        FileSystem::dirContents($path),
-                        static fn($filename) => str_ends_with($filename, '.json')
+                        FileSystem::dirContents($normpath),
+                        static fn($filename) => FileSystem::isCollectionFile($filename)
                     );
                     $this->collectionPaths = array_unique(array_merge($this?->collectionPaths ?? [], $files));
                     break;
+
                 case '-p':
                 case '--preserve':
                     $this->preserveOutput = true;
                     break;
+
                 case '--http':
                     $this->formats[ConvertFormat::Http->name] = ConvertFormat::Http;
                     break;
+
                 case '--curl':
                     $this->formats[ConvertFormat::Curl->name] = ConvertFormat::Curl;
                     break;
+
                 case '--wget':
                     $this->formats[ConvertFormat::Wget->name] = ConvertFormat::Wget;
                     break;
+
                 case '-v':
                 case '--version':
                     die(implode(PHP_EOL, $this->version()) . PHP_EOL);
+
                 case '-h':
                 case '--help':
                     die(implode(PHP_EOL, $this->usage()) . PHP_EOL);