diff --git a/cmd/tools/vdoc/utils.v b/cmd/tools/vdoc/utils.v
index 304d4d9ac4..09b87a8a07 100644
--- a/cmd/tools/vdoc/utils.v
+++ b/cmd/tools/vdoc/utils.v
@@ -49,7 +49,7 @@ fn trim_doc_node_description(description string) string {
 	if dn_description.len > 80 {
 		dn_description = dn_description[..80]
 	}
-	if '\n' in dn_description {
+	if dn_description.contains('\n') {
 		dn_description = dn_description.split('\n')[0]
 	}
 	// if \ is last character, it ends with \" which leads to a JS error
@@ -99,7 +99,7 @@ fn is_included(path string, ignore_paths []string) bool {
 		return true
 	}
 	for ignore_path in ignore_paths {
-		if ignore_path !in path {
+		if !path.contains(ignore_path) {
 			continue
 		}
 		return false
diff --git a/cmd/tools/vtest-self.v b/cmd/tools/vtest-self.v
index 8ba7361570..752156d548 100644
--- a/cmd/tools/vtest-self.v
+++ b/cmd/tools/vtest-self.v
@@ -220,22 +220,22 @@ fn main() {
 	mut asan_compiler := false
 	mut msan_compiler := false
 	for arg in args {
-		if '-asan-compiler' in arg {
+		if arg.contains('-asan-compiler') {
 			asan_compiler = true
 		}
-		if '-msan-compiler' in arg {
+		if arg.contains('-msan-compiler') {
 			msan_compiler = true
 		}
-		if '-Werror' in arg {
+		if arg.contains('-Werror') {
 			werror = true
 		}
-		if '-fsanitize=memory' in arg {
+		if arg.contains('-fsanitize=memory') {
 			sanitize_memory = true
 		}
-		if '-fsanitize=address' in arg {
+		if arg.contains('-fsanitize=address') {
 			sanitize_address = true
 		}
-		if '-fsanitize=undefined' in arg {
+		if arg.contains('-fsanitize=undefined') {
 			sanitize_undefined = true
 		}
 	}
diff --git a/vlib/term/ui/termios_nix.c.v b/vlib/term/ui/termios_nix.c.v
index 6a338281ca..28eb8385ac 100644
--- a/vlib/term/ui/termios_nix.c.v
+++ b/vlib/term/ui/termios_nix.c.v
@@ -196,7 +196,7 @@ fn supports_truecolor() bool {
 		buf[len] = 0
 		s = tos(buf, len)
 	}
-	return '1:2:3' in s
+	return s.contains('1:2:3')
 }
 
 fn termios_reset() {
@@ -296,14 +296,17 @@ fn single_char(buf string) &Event {
 				utf8: event.utf8
 				code: KeyCode(96 | ch)
 				modifiers: .ctrl
-			} }
-		65...90 { event = &Event{
+			}
+		}
+		65...90 {
+			event = &Event{
 				typ: event.typ
 				ascii: event.ascii
 				utf8: event.utf8
 				code: KeyCode(32 | ch)
 				modifiers: .shift
-			} }
+			}
+		}
 		else {}
 	}
 
diff --git a/vlib/v/doc/doc.v b/vlib/v/doc/doc.v
index 11cc9eaf4f..cdb8d9fd70 100644
--- a/vlib/v/doc/doc.v
+++ b/vlib/v/doc/doc.v
@@ -344,7 +344,7 @@ pub fn (mut d Doc) generate() ? {
 	} else {
 		os.real_path(os.dir(d.base_path))
 	}
-	d.is_vlib = 'vlib' !in d.base_path
+	d.is_vlib = !d.base_path.contains('vlib')
 	project_files := os.ls(d.base_path) or { return err }
 	v_files := d.prefs.should_compile_filtered_files(d.base_path, project_files)
 	if v_files.len == 0 {
@@ -374,7 +374,7 @@ pub fn (mut d Doc) file_asts(file_asts []ast.File) ? {
 	mut fname_has_set := false
 	d.orig_mod_name = file_asts[0].mod.name
 	for i, file_ast in file_asts {
-		if d.filename.len > 0 && d.filename in file_ast.path && !fname_has_set {
+		if d.filename.len > 0 && file_ast.path.contains(d.filename) && !fname_has_set {
 			d.filename = file_ast.path
 			fname_has_set = true
 		}
diff --git a/vlib/v/fmt/fmt.v b/vlib/v/fmt/fmt.v
index 5390bff3f5..5d77592d6d 100644
--- a/vlib/v/fmt/fmt.v
+++ b/vlib/v/fmt/fmt.v
@@ -1767,7 +1767,7 @@ pub fn (mut f Fmt) if_expr(node ast.IfExpr) {
 				cond_len := f.out.len - cur_pos
 				is_cond_wrapped := cond_len > 0
 					&& (branch.cond is ast.IfGuardExpr || branch.cond is ast.CallExpr)
-					&& '\n' in f.out.last_n(cond_len)
+					&& f.out.last_n(cond_len).contains('\n')
 				if is_cond_wrapped {
 					f.writeln('')
 				} else {