diff --git a/ExternalApps/HelloWorld/tactility.properties b/ExternalApps/HelloWorld/tactility.properties
new file mode 100644
index 00000000..14c0bdfb
--- /dev/null
+++ b/ExternalApps/HelloWorld/tactility.properties
@@ -0,0 +1,2 @@
+[sdk]
+version = 0.4.0-dev
diff --git a/ExternalApps/HelloWorld/ttbuild.py b/ExternalApps/HelloWorld/ttbuild.py
index 5f7c9a15..204b969a 100644
--- a/ExternalApps/HelloWorld/ttbuild.py
+++ b/ExternalApps/HelloWorld/ttbuild.py
@@ -2,10 +2,29 @@ import sys
 import os
 import urllib.request
 import zipfile
+import configparser
+import time
+import json
 
 esp_platforms = ["esp32", "esp32s3"]
 ttbuild_path = '.ttbuild'
 ttbuild_version = '0.1.0'
+ttbuild_properties_file = 'tactility.properties'
+ttbuild_cdn = "https://cdn.tactility.one"
+
+def download_file(url, filepath):
+    request = urllib.request.Request(
+        url,
+        data=None,
+        headers={
+            'User-Agent': f"Tactility Build Tool {ttbuild_version}"
+        }
+    )
+    response = urllib.request.urlopen(request)
+    file = open(filepath, mode='wb')
+    file.write(response.read())
+    file.close()
+    return True
 
 def print_warning(message):
     if sys.platform == 'win32':
@@ -45,6 +64,8 @@ def validate_environment():
         exit_with_error("IDF is not installed or activated. Ensure you installed the toolset and ran the export command.")
     if os.environ.get('TACTILITY_SDK_PATH') is not None:
         print_warning("TACTILITY_SDK_PATH is set, but will be ignored by this command")
+    if not os.path.exists(ttbuild_properties_file):
+        exit_with_error(f"{ttbuild_properties_file} file not found")
 
 def setup_environment():
     os.makedirs(ttbuild_path, exist_ok=True)
@@ -52,36 +73,50 @@ def setup_environment():
 def get_sdk_dir(version, platform):
     return os.path.join(ttbuild_path, f"{version}-{platform}", 'TactilitySDK')
 
+def get_sdk_version():
+    parser = configparser.RawConfigParser()
+    parser.read(ttbuild_properties_file)
+    sdk_dict = dict(parser.items('sdk'))
+    if not 'version' in sdk_dict:
+        exit_with_error(f"Could not find 'version' in [sdk] section in {ttbuild_properties_file}")
+    return sdk_dict['version']
+
 def get_sdk_root_dir(version, platform):
     return os.path.join(ttbuild_path, f"{version}-{platform}")
 
 def get_sdk_url(version, platform):
-    return f"https://cdn.tactility.one/TactilitySDK-{version}-{platform}.zip"
+    return f"{ttbuild_cdn}/TactilitySDK-{version}-{platform}.zip"
 
 def sdk_exists(version, platform):
     sdk_dir = get_sdk_dir(version, platform)
     return os.path.isdir(sdk_dir)
 
+def should_update_sdk_json():
+    json_filepath = os.path.join(ttbuild_path, "sdk.json")
+    if os.path.exists(json_filepath):
+        json_modification_time = os.path.getmtime(json_filepath)
+        now = time.time()
+        minimum_seconds_difference = 3600
+        return (now - json_modification_time) > minimum_seconds_difference
+    else:
+        return True
+
+def update_sdk_json():
+    json_url = f"{ttbuild_cdn}/sdk.json"
+    json_filepath = os.path.join(ttbuild_path, "sdk.json")
+    return download_file(json_url, json_filepath)
+
 def sdk_download(version, platform):
     sdk_root_dir = get_sdk_root_dir(version, platform)
     os.makedirs(sdk_root_dir, exist_ok=True)
     sdk_url = get_sdk_url(version, platform)
     print(f"Downloading SDK version {version} for {platform} from {sdk_url}")
-    request = urllib.request.Request(
-        sdk_url,
-        data=None,
-        headers={
-            'User-Agent': f"Tactility Build Tool {ttbuild_version}"
-        }
-    )
-    response = urllib.request.urlopen(request)
     filepath = os.path.join(sdk_root_dir, f"{version}-{platform}.zip")
-    file = open(filepath, mode='wb')
-    file.write(response.read())
-    file.close()
-    with zipfile.ZipFile(filepath, 'r') as zip_ref:
-        zip_ref.extractall(sdk_root_dir)
-    return True
+    if download_file(sdk_url, filepath):
+        with zipfile.ZipFile(filepath, 'r') as zip_ref:
+            zip_ref.extractall(sdk_root_dir)
+    else:
+        exit_with_error("Failed to download SDK")
 
 def sdk_download_all(version, platforms):
     for platform in platforms:
@@ -90,6 +125,16 @@ def sdk_download_all(version, platforms):
         else:
             print(f"Using cached download for SDK version {version} and platform {platform}")
 
+def validate_version_and_platforms(sdk_json, sdk_version, platforms_to_build):
+    version_map = sdk_json['versions']
+    if not sdk_version in version_map:
+        exit_with_error(f"Version not found: {sdk_version}")
+    version_data = version_map[sdk_version]
+    available_platforms = version_data['platforms']
+    for desired_platform in platforms_to_build:
+        if not desired_platform in available_platforms:
+            exit_with_error(f"Platform {desired_platform} is not available. Available ones: {available_platforms}")
+
 if __name__ == "__main__":
     print(f"Tactility Build System v{ttbuild_version}")
     # Environment
@@ -103,9 +148,17 @@ if __name__ == "__main__":
     if not is_valid_platform_name(platform_arg):
         print_help()
         exit_with_error("Invalid platform name")
+    # Update SDK cache
+    if should_update_sdk_json():
+        update_sdk_json()
+    json_file_path = os.path.join(ttbuild_path, 'sdk.json')
+    json_file = open(json_file_path)
+    sdk_json = json.load(json_file)
+    if not 'versions' in sdk_json:
+        exit_with_error("version data not found in sdk.json")
     # Build
     platforms_to_build = esp_platforms if platform_arg == "all" else [platform_arg]
-    sdk_version = '0.4.0-dev'
+    sdk_version = get_sdk_version()
+    validate_version_and_platforms(sdk_json, sdk_version, platforms_to_build)
     sdk_download_all(sdk_version, platforms_to_build)
     build(sdk_version, platforms_to_build)
-