diff --git a/src/cli/cli.odin b/src/cli/cli.odin
index 08a6c9b..243e75d 100644
--- a/src/cli/cli.odin
+++ b/src/cli/cli.odin
@@ -5,6 +5,8 @@ import "core:fmt"
 import "core:os"
 import "core:strings"
 
+// -----------------------------------------
+
 Options :: struct {
 	verbose:     bool `args:"name=verbose"                    usage:"Enable verbose output"`,
 	compression: u16 `args:"name=compression"                 usage:"Compression level, 0-12"`,
@@ -14,25 +16,31 @@ Options :: struct {
 	// overflow:    [dynamic]string,
 }
 
-parse :: proc(working_dir: string) -> Options {
+Error :: union #shared_nil {
+	flags.Error,
+}
+
+// -----------------------------------------
+
+parse :: proc(working_dir: string) -> (Options, Error) {
 	opts: Options
 
 	err := flags.parse(&opts, os.args[1:], .Unix)
 
 	if err != nil {
 		flags.print_errors(typeid_of(Options), err, os.args[0], .Unix)
-		os.exit(1)
+		return {}, err
 	}
 
 	verify(opts, working_dir)
 
-	return opts
+	return opts, nil
 }
 
 @(private)
-verify :: proc(opts: Options, working_dir: string) {
+verify :: proc(opts: Options, working_dir: string) -> Error {
 	if opts.compression > 12 {
-		throw_error(
+		return throw_error(
 			`Invalid compression "%d". Compression higher than allowed maximum.`,
 			opts.compression,
 		)
@@ -40,13 +48,16 @@ verify :: proc(opts: Options, working_dir: string) {
 
 	input_path := os.name(opts.input)
 	if !os.is_dir(input_path) {
-		throw_error(`Invalid input "%v". Should be a directory`, input_path)
+		return throw_error(
+			`Invalid input "%v". Should be a directory`,
+			input_path,
+		)
 	}
 
 	if opts.output != nil {
 		output_path := os.name(opts.output)
 		if !os.is_dir(output_path) {
-			throw_error(
+			return throw_error(
 				`Invalid output "%v". Should be a directory`,
 				output_path,
 			)
@@ -54,18 +65,20 @@ verify :: proc(opts: Options, working_dir: string) {
 	}
 
 	if !strings.has_prefix(input_path, working_dir) {
-		throw_error(
+		return throw_error(
 			`Invalid input "%v". Should be a subdirectory of the working directory.`,
 			input_path,
 		)
 	}
+
+	return nil
 }
 
 @(private)
-throw_error :: proc(fmt_str: string, args: ..any) {
+throw_error :: proc(fmt_str: string, args: ..any) -> Error {
 	err := flags.Validation_Error {
 		message = fmt.tprintf(fmt_str, ..args),
 	}
 	flags.print_errors(typeid_of(Options), err, os.args[0], .Unix)
-	os.exit(1)
+	return err
 }
diff --git a/src/file/file.odin b/src/file/file.odin
index 9c38eae..818726d 100644
--- a/src/file/file.odin
+++ b/src/file/file.odin
@@ -5,12 +5,26 @@ import "core:os"
 
 // -----------------------------------------
 
-get_working_dir :: proc(allocator := context.allocator) -> string {
+Error :: union #shared_nil {
+	os.Error,
+	File_Error,
+}
+
+File_Error :: enum u8 {
+	None            = 0,
+	Not_A_Directory = 1,
+	Unimplemented   = 127,
+	Okay            = None,
+}
+
+// -----------------------------------------
+
+get_working_dir :: proc(allocator := context.allocator) -> (string, Error) {
 	wd, err := os.get_working_directory(allocator)
 	if err != nil {
 		fmt.eprintln("error: get working directory failed:", err)
-		os.exit(1)
+		return {}, err
 	}
 
-	return wd
+	return wd, nil
 }
diff --git a/src/file/list_dir.odin b/src/file/list_dir.odin
index 378bbb6..dfbf2f9 100644
--- a/src/file/list_dir.odin
+++ b/src/file/list_dir.odin
@@ -19,9 +19,17 @@ list_dir_recursive :: proc(
 	f: ^os.File,
 	working_dir: string,
 	allocator := context.allocator,
-) -> [dynamic]File_Entry {
+) -> (
+	entries: [dynamic]File_Entry,
+	err: Error,
+) {
 	path := os.name(f)
-	return list_dir_recursive_by_path_impl(path, working_dir, allocator)
+	result := list_dir_recursive_by_path_impl(
+		path,
+		working_dir,
+		allocator,
+	) or_return
+	return result, nil
 }
 
 // Returning `[dynamic]File_Entry` and each relpath `string` inside it are owned by the caller.
@@ -29,8 +37,16 @@ list_dir_recursive_by_path :: proc(
 	path: string,
 	working_dir: string,
 	allocator := context.allocator,
-) -> [dynamic]File_Entry {
-	return list_dir_recursive_by_path_impl(path, working_dir, allocator)
+) -> (
+	entries: [dynamic]File_Entry,
+	err: Error,
+) {
+	result := list_dir_recursive_by_path_impl(
+		path,
+		working_dir,
+		allocator,
+	) or_return
+	return result, nil
 }
 
 // Frees every owning relpath string then the dynamic array itself.
@@ -46,10 +62,13 @@ list_dir_recursive_by_path_impl :: proc(
 	path: string,
 	working_dir: string,
 	allocator: runtime.Allocator,
-) -> [dynamic]File_Entry {
+) -> (
+	[dynamic]File_Entry,
+	Error,
+) {
 	if !os.is_dir(path) {
 		fmt.eprintln("error: path is not a directory:", path)
-		os.exit(1)
+		return {}, .Not_A_Directory
 	}
 
 	result := make([dynamic]File_Entry, allocator)
@@ -62,7 +81,7 @@ list_dir_recursive_by_path_impl :: proc(
 		list_dir_queue(&queue, &result, working_dir, allocator)
 	}
 
-	return result // owning [dynamic]
+	return result, nil // owning [dynamic]
 }
 
 @(private)
@@ -71,7 +90,7 @@ list_dir_queue :: proc(
 	result: ^[dynamic]File_Entry,
 	working_dir: string,
 	allocator: runtime.Allocator,
-) {
+) -> Error {
 	assert(len(queue) > 0, "queue must not be empty")
 
 	path := pop(queue)
@@ -80,14 +99,14 @@ list_dir_queue :: proc(
 	f, open_err := os.open(path, {.Read})
 	if open_err != nil {
 		fmt.eprintln("error: open failed:", open_err)
-		os.exit(1)
+		return open_err
 	}
 	defer os.close(f)
 
 	entries, read_err := os.read_all_directory(f, allocator)
 	if read_err != nil {
 		fmt.eprintln("error: read directory failed:", read_err)
-		os.exit(1)
+		return read_err
 	}
 	defer os.file_info_slice_delete(entries, allocator)
 
@@ -118,4 +137,6 @@ list_dir_queue :: proc(
 			case: // skip other types
 		}
 	}
+
+	return nil
 }
diff --git a/src/main.odin b/src/main.odin
index ae263b3..28daff5 100644
--- a/src/main.odin
+++ b/src/main.odin
@@ -8,39 +8,50 @@ import "src:file"
 
 VERSION :: #config(VERSION, "dev")
 
+CLI_ERR :: 1
+WORKING_DIR_ERR :: 2
+LIST_DIR_ERR :: 3
+WRITE_ASSETS_ERR :: 4
+WRITE_METADATA_ERR :: 5
+
+// -----------------------------------------
+
 main :: proc() {
-	working_dir := file.get_working_dir()
+	working_dir, wd_err := file.get_working_dir()
+	if wd_err != nil do os.exit(WORKING_DIR_ERR)
 	defer delete(working_dir)
 
-	opts := cli.parse(working_dir)
+	opts, c_err := cli.parse(working_dir)
+	if c_err != nil do os.exit(CLI_ERR)
 
 	// fmt.println("verbose:", opts.verbose)
 	// fmt.println("compression:", opts.compression)
 	// fmt.println("size:", opts.size)
 
-	entries := file.list_dir_recursive(opts.input, working_dir)
+	entries, e_err := file.list_dir_recursive(opts.input, working_dir)
+	if e_err != nil do os.exit(LIST_DIR_ERR)
 	defer file.delete_entries(&entries)
 
 	w := chunks.writer_init(cast(u64)len(entries))
 	defer chunks.writer_destroy(&w)
 
-	err := chunks.write_assets(
+	wa_err := chunks.write_assets(
 		&w,
 		opts.output,
 		entries[:],
 		opts.size,
 		opts.compression,
 	)
-	if err != nil do os.exit(1)
+	if wa_err != nil do os.exit(WRITE_ASSETS_ERR)
 
-	chunks.write_metadata(
+	wm_err := chunks.write_metadata(
 		&w,
 		opts.output,
 		entries[:],
 		opts.size,
 		opts.compression,
 	)
-	if err != nil do os.exit(2)
+	if wm_err != nil do os.exit(WRITE_METADATA_ERR)
 }
 
 // TODO: .chunkignore