diff --git a/pyproject.toml b/pyproject.toml
index f361a18..5cbb9d3 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -10,6 +10,7 @@ requires-python = ">=3.10"
 dependencies = [
   "toml",
   "alive-progress",
+  "types-toml",
 ]
 authors = [
   {name = "Alexander Wainwright", email = "code@figtree.dev"},
@@ -35,7 +36,7 @@ line-length = 80
 select = [
   "B",
   "W",
-  # "ANN",
+  "ANN",
   "FIX",
   "S",
   "F",        # Pyflakes rules
diff --git a/src/emulsion/config.py b/src/emulsion/config.py
index a0c49de..a7130bf 100644
--- a/src/emulsion/config.py
+++ b/src/emulsion/config.py
@@ -1,12 +1,13 @@
 import copy
 import os
 from pathlib import Path
+from typing import Any
 
 import toml
 
 # Default Schema
 # This defines the "First Class" feel of the app, but is fully overridable.
-DEFAULT_CONFIG = {
+DEFAULT_CONFIG: dict[str, Any] = {
 	"sidecar": {
 		"extension": ".xmp"
 	},
@@ -55,19 +56,19 @@ DEFAULT_CONFIG = {
 }
 
 
-def get_config_path():
+def get_config_path() -> Path:
 	xdg_config_home = os.environ.get(
-		'XDG_CONFIG_HOME', Path('~/.config').expanduser()
+		'XDG_CONFIG_HOME', str(Path('~/.config').expanduser())
 	)
 	return Path(xdg_config_home) / 'emulsion' / 'config.toml'
 
 
 class ConfigLoader:
-	def __init__(self, path=None):
+	def __init__(self, path: Path | None = None) -> None:
 		self.path: Path = path or get_config_path()
-		self.config = copy.deepcopy(DEFAULT_CONFIG)
+		self.config: dict[str, Any] = copy.deepcopy(DEFAULT_CONFIG)
 
-	def load(self):
+	def load(self) -> dict[str, Any]:
 		"""
 		Loads the config from disk and merges it into the defaults.
 		Returns the full config dictionary.
@@ -85,7 +86,7 @@ class ConfigLoader:
 
 		return self.config
 
-	def _merge(self, base, update):
+	def _merge(self, base: dict[str, Any], update: dict[str, Any]) -> None:
 		"""
 		Recursively merges 'update' dict into 'base' dict.
 		"""
@@ -99,7 +100,7 @@ class ConfigLoader:
 			else:
 				base[key] = value
 
-	def save_defaults(self, current_defaults):
+	def save_defaults(self, current_defaults: dict[str, Any]) -> bool:
 		"""
 		Helpers to write a new config file (for --init-config). This is a bit
 		tricky because we don't want to just dump the massive DEFAULT_CONFIG. We
@@ -111,13 +112,13 @@ class ConfigLoader:
 		# doesn't do that.
 
 		# Ensure directory exists
-		self.path.parent.mkdir(parents=True)
+		self.path.parent.mkdir(parents=True, exist_ok=True)
 
 		# We probably only want to write if it doesn't exist, to avoid
 		# clobbering.
-		if self.path.exists:
+		if self.path.exists():
 			return False
 
-		with self.path.open(encoding='utf-8') as f:
+		with self.path.open('w', encoding='utf-8') as f:
 			toml.dump(current_defaults, f)
 		return True
diff --git a/src/emulsion/executor.py b/src/emulsion/executor.py
index 468ca1d..945b091 100644
--- a/src/emulsion/executor.py
+++ b/src/emulsion/executor.py
@@ -1,21 +1,28 @@
 import datetime
 import shlex
 import subprocess
+from argparse import Namespace
 from concurrent.futures import ThreadPoolExecutor, as_completed
 from pathlib import Path
+from typing import Any
 
 from alive_progress import alive_bar
 
 
 class Executor:
-	def __init__(self, config):
+	def __init__(self, config: dict[str, Any]) -> None:
 		self.config = config
-		self.mappings = config.get('mappings', {})
-		self.sidecar_ext = config.get('sidecar', {}).get('extension', '.xmp')
+		self.mappings: dict[str, Any] = config.get('mappings', {})
+		self.sidecar_ext: str = config.get(
+				'sidecar', {}).get('extension', '.xmp')
 		if not self.sidecar_ext.startswith('.'):
 			self.sidecar_ext = f".{self.sidecar_ext}"
 
-	def run_batch(self, files, resolved_values, options):
+	def run_batch(
+		self, files: list[str],
+		resolved_values: dict[str, str],
+		options: Namespace
+	) -> None:
 		"""
 		Main execution entry point.
 		files: List of file paths
@@ -23,11 +30,11 @@ class Executor:
 		options: Dictionary/Namespace of process options (dry_run, workers,
 		         base_date, etc.)
 		"""
-		extensions = ['.jpg', '.jpeg', '.tif', '.tiff']
 		# Filter supported files
+		extensions = ['.jpg', '.jpeg', '.tif', '.tiff']
 		valid_files = [
 			f for f in files
-			if Path(f).suffix in extensions
+			if Path(f).suffix.lower() in extensions
 		]
 
 		if not valid_files:
@@ -55,7 +62,7 @@ class Executor:
 		print(f"Processing {total_files} file(s)...")
 
 		# Prepare tasks
-		tasks = []
+		tasks: list[tuple[list[str], str, str]] = []
 		for i, f in enumerate(valid_files):
 			# Calculate timestamp
 			ts_dt = base_dt + datetime.timedelta(seconds=i * time_increment)
@@ -63,7 +70,7 @@ class Executor:
 
 			# Determine file targets (Sidecar logic)
 			target_path, sidecar_source = self._determine_paths(
-				f, options.embed
+				Path(f), options.embed
 			)
 
 			# Build Command
@@ -98,14 +105,16 @@ class Executor:
 
 				bar()
 
-	def _determine_paths(self, original_file, embed):
+	def _determine_paths(
+			self, original_file: Path, embed: bool
+	) -> tuple[Path, Path | None]:
 		"""
 		Returns (target_path, sidecar_source_if_needed)
 		"""
 		if embed:
-			return original_file, None
+			return Path(original_file), None
 
-		target_path = f"{original_file}{self.sidecar_ext}"
+		target_path = Path(f'{original_file}{self.sidecar_ext}')
 
 		# If sidecar doesn't exist, we need to tell ExifTool to read from source
 		# and write to the new sidecar file.
@@ -115,8 +124,12 @@ class Executor:
 		return target_path, None
 
 	def _build_cmd(
-		self, file_path, field_values, timestamp_str, sidecar_source=None
-	):
+		self,
+		file_path: Path,
+		field_values: dict[str, str],
+		timestamp_str: str,
+		sidecar_source: Path | None = None
+	) -> list[str]:
 		current_year = datetime.datetime.now().year
 
 		# Core setup
@@ -153,14 +166,14 @@ class Executor:
 		if sidecar_source:
 			# -srcfile SOURCE TARGET
 			cmd.append("-srcfile")
-			cmd.append(file_path)
-			cmd.append(sidecar_source)
+			cmd.append(str(file_path))
+			cmd.append(str(sidecar_source))
 		else:
-			cmd.append(file_path)
+			cmd.append(str(file_path))
 
 		return cmd
 
-	def _run_exiftool(self, cmd, dry_run):
+	def _run_exiftool(self, cmd: list[str], dry_run: bool) -> tuple[bool, str]:
 		if dry_run:
 			safe_cmd = shlex.join(cmd)
 			return True, f"[DRY RUN] {safe_cmd}"
@@ -178,7 +191,7 @@ class Executor:
 		except FileNotFoundError:
 			return False, "Error: 'exiftool' not found. Please install it."
 
-	def _parse_date(self, dt_str):
+	def _parse_date(self, dt_str: str | None) -> datetime.datetime:
 		if not dt_str:
 			# Should be handled by resolver/validator, but safe fallback
 			return datetime.datetime.now()
diff --git a/src/emulsion/main.py b/src/emulsion/main.py
index b310e8f..01c40a5 100644
--- a/src/emulsion/main.py
+++ b/src/emulsion/main.py
@@ -3,20 +3,21 @@ import datetime
 import os
 import sys
 from importlib.metadata import PackageNotFoundError, version
+from typing import Any
 
 from emulsion.config import ConfigLoader
 from emulsion.executor import Executor
 from emulsion.resolver import ValueResolver
 
 
-def get_version():
+def get_version() -> str:
 	try:
 		return version('emulsion')
 	except PackageNotFoundError:
 		return 'unknown'
 
 
-def parse_args():
+def parse_args() -> argparse.Namespace:
 	parser = argparse.ArgumentParser(
 		description='A tool for updating exif tags'
 	)
@@ -107,7 +108,7 @@ def parse_args():
 	return parser.parse_args()
 
 
-def prompt_for_defaults(config):
+def prompt_for_defaults(config: dict[str, Any]) -> None:
 	"""
 	Prompts the user for default values to populate the initial config.
 	"""
@@ -140,7 +141,7 @@ def prompt_for_defaults(config):
 			print('Invalid number, keeping default.')
 
 
-def main():
+def main() -> None:
 	try:
 		# 1. Load Config
 		loader = ConfigLoader()
@@ -188,7 +189,7 @@ def main():
 
 		# 3. Prepare Inputs for Resolver
 		# We need to mash --author and --field author=... into one dict
-		user_inputs = {}
+		user_inputs: dict[str, Any] = {}
 
 		# First-Class args
 		for field in ['author', 'lab', 'make', 'model', 'lens', 'film']:
diff --git a/src/emulsion/resolver.py b/src/emulsion/resolver.py
index a2f14d0..2f719fd 100644
--- a/src/emulsion/resolver.py
+++ b/src/emulsion/resolver.py
@@ -1,16 +1,19 @@
 import sys
+from typing import Any
 
 
 class ValueResolver:
-	def __init__(self, config):
+	def __init__(self, config: dict[str, Any]) -> None:
 		"""
 		config: The loaded configuration dictionary containing 'mappings' and
 		'defaults'.
 		"""
-		self.mappings = config.get('mappings', {})
-		self.defaults = config.get('defaults', {})
+		self.mappings: dict[str, Any] = config.get('mappings', {})
+		self.defaults: dict[str, Any] = config.get('defaults', {})
 
-	def resolve(self, cli_args, interactive=True):
+	def resolve(
+			self, cli_args: dict[str, Any], interactive: bool = True
+		) -> dict[str, str]:
 		"""
 		Resolves the final values for all fields.
 
@@ -40,7 +43,7 @@ class ValueResolver:
 		# 3. Identify Prompts
 		# We look at the 'mappings' to see which fields want to be prompted.
 		if interactive:
-			fields_to_prompt = []
+			fields_to_prompt: list[str] = []
 			for field_name, schema in self.mappings.items():
 				# Check if prompt is requested
 				if (isinstance(schema, dict)
@@ -62,9 +65,12 @@ class ValueResolver:
 				sys.exit(1)
 
 		# Remove any fields that are still None/Empty (optional, but cleaner)
-		return {k: v for k, v in resolved.items() if v}
+		# Also cast values to string
+		return {k: str(v) for k, v in resolved.items() if v}
 
-	def _prompt_user(self, field_name, resolved_dict):
+	def _prompt_user(
+			self, field_name: str, resolved_dict: dict[str, Any]
+	) -> None:
 		"""
 		Helper to prompt a single field.
 		"""