diff --git a/common/pango.c b/common/pango.c
index e04bf80f3..288569b30 100644
--- a/common/pango.c
+++ b/common/pango.c
@@ -84,18 +84,11 @@ void get_text_size(cairo_t *cairo, const PangoFontDescription *desc, int *width,
 		int *baseline, double scale, bool markup, const char *fmt, ...) {
 	va_list args;
 	va_start(args, fmt);
-	// Add one since vsnprintf excludes null terminator.
-	int length = vsnprintf(NULL, 0, fmt, args) + 1;
+	char *buf = vformat_str(fmt, args);
 	va_end(args);
-
-	char *buf = malloc(length);
 	if (buf == NULL) {
-		sway_log(SWAY_ERROR, "Failed to allocate memory");
 		return;
 	}
-	va_start(args, fmt);
-	vsnprintf(buf, length, fmt, args);
-	va_end(args);
 
 	PangoLayout *layout = get_pango_layout(cairo, desc, buf, scale, markup);
 	pango_cairo_update_layout(cairo, layout);
@@ -104,6 +97,7 @@ void get_text_size(cairo_t *cairo, const PangoFontDescription *desc, int *width,
 		*baseline = pango_layout_get_baseline(layout) / PANGO_SCALE;
 	}
 	g_object_unref(layout);
+
 	free(buf);
 }
 
@@ -125,18 +119,11 @@ void render_text(cairo_t *cairo, const PangoFontDescription *desc,
 		double scale, bool markup, const char *fmt, ...) {
 	va_list args;
 	va_start(args, fmt);
-	// Add one since vsnprintf excludes null terminator.
-	int length = vsnprintf(NULL, 0, fmt, args) + 1;
+	char *buf = vformat_str(fmt, args);
 	va_end(args);
-
-	char *buf = malloc(length);
 	if (buf == NULL) {
-		sway_log(SWAY_ERROR, "Failed to allocate memory");
 		return;
 	}
-	va_start(args, fmt);
-	vsnprintf(buf, length, fmt, args);
-	va_end(args);
 
 	PangoLayout *layout = get_pango_layout(cairo, desc, buf, scale, markup);
 	cairo_font_options_t *fo = cairo_font_options_create();
@@ -146,5 +133,6 @@ void render_text(cairo_t *cairo, const PangoFontDescription *desc,
 	pango_cairo_update_layout(cairo, layout);
 	pango_cairo_show_layout(cairo, layout);
 	g_object_unref(layout);
+
 	free(buf);
 }
diff --git a/sway/commands.c b/sway/commands.c
index 0ea44129e..55eda183c 100644
--- a/sway/commands.c
+++ b/sway/commands.c
@@ -489,20 +489,10 @@ struct cmd_results *cmd_results_new(enum cmd_status status,
 	}
 	results->status = status;
 	if (format) {
-		char *error = NULL;
 		va_list args;
 		va_start(args, format);
-		int slen = vsnprintf(NULL, 0, format, args);
+		results->error = vformat_str(format, args);
 		va_end(args);
-		if (slen > 0) {
-			error = malloc(slen + 1);
-			if (error != NULL) {
-				va_start(args, format);
-				vsnprintf(error, slen + 1, format, args);
-				va_end(args);
-			}
-		}
-		results->error = error;
 	} else {
 		results->error = NULL;
 	}
diff --git a/sway/commands/bar.c b/sway/commands/bar.c
index 8571d282c..22756acbf 100644
--- a/sway/commands/bar.c
+++ b/sway/commands/bar.c
@@ -73,12 +73,10 @@ struct cmd_results *cmd_bar(int argc, char **argv) {
 		}
 		++argv; --argc;
 	} else if (config->reading && !config->current_bar) {
-		int len = snprintf(NULL, 0, "bar-%d", config->bars->length) + 1;
-		id = malloc(len * sizeof(char));
+		id = format_str("bar-%d", config->bars->length);
 		if (!id) {
 			return cmd_results_new(CMD_FAILURE, "Unable to allocate bar id");
 		}
-		snprintf(id, len, "bar-%d", config->bars->length);
 	} else if (!config->reading && strcmp(argv[0], "mode") != 0 &&
 			strcmp(argv[0], "hidden_state") != 0) {
 		if (is_subcommand(argv[0])) {
diff --git a/sway/config.c b/sway/config.c
index f5efa98a8..8c8c148d9 100644
--- a/sway/config.c
+++ b/sway/config.c
@@ -924,23 +924,18 @@ void config_add_swaynag_warning(char *fmt, ...) {
 	if (config->reading && !config->validating) {
 		va_list args;
 		va_start(args, fmt);
-		size_t length = vsnprintf(NULL, 0, fmt, args) + 1;
+		char *str = vformat_str(fmt, args);
 		va_end(args);
-
-		char *temp = malloc(length + 1);
-		if (!temp) {
-			sway_log(SWAY_ERROR, "Failed to allocate buffer for warning.");
+		if (str == NULL) {
 			return;
 		}
 
-		va_start(args, fmt);
-		vsnprintf(temp, length, fmt, args);
-		va_end(args);
-
 		swaynag_log(config->swaynag_command, &config->swaynag_config_errors,
 			"Warning on line %i (%s) '%s': %s",
 			config->current_config_line_number, config->current_config_path,
-			config->current_config_line, temp);
+			config->current_config_line, str);
+
+		free(str);
 	}
 }
 
diff --git a/sway/config/output.c b/sway/config/output.c
index 45d2441b1..6fb29ded9 100644
--- a/sway/config/output.c
+++ b/sway/config/output.c
@@ -162,13 +162,10 @@ static void merge_id_on_name(struct output_config *oc) {
 	char id[128];
 	output_get_identifier(id, sizeof(id), output);
 
-	size_t size = snprintf(NULL, 0, "%s on %s", id, name) + 1;
-	char *id_on_name = malloc(size);
+	char *id_on_name = format_str("%s on %s", id, name);
 	if (!id_on_name) {
-		sway_log(SWAY_ERROR, "Failed to allocate id on name string");
 		return;
 	}
-	snprintf(id_on_name, size, "%s on %s", id, name);
 
 	int i = list_seq_find(config->output_configs, output_name_cmp, id_on_name);
 	if (i >= 0) {
@@ -633,9 +630,7 @@ static struct output_config *get_output_config(char *identifier,
 	struct output_config *oc_name = NULL;
 	struct output_config *oc_id = NULL;
 
-	size_t length = snprintf(NULL, 0, "%s on %s", identifier, name) + 1;
-	char *id_on_name = malloc(length);
-	snprintf(id_on_name, length, "%s on %s", identifier, name);
+	char *id_on_name = format_str("%s on %s", identifier, name);
 	int i = list_seq_find(config->output_configs, output_name_cmp, id_on_name);
 	if (i >= 0) {
 		oc_id_on_name = config->output_configs->items[i];
diff --git a/sway/input/cursor.c b/sway/input/cursor.c
index 15687993b..75d055cd6 100644
--- a/sway/input/cursor.c
+++ b/sway/input/cursor.c
@@ -1273,11 +1273,7 @@ uint32_t get_mouse_bindsym(const char *name, char **error) {
 		// Get event code from name
 		int code = libevdev_event_code_from_name(EV_KEY, name);
 		if (code == -1) {
-			size_t len = snprintf(NULL, 0, "Unknown event %s", name) + 1;
-			*error = malloc(len);
-			if (*error) {
-				snprintf(*error, len, "Unknown event %s", name);
-			}
+			*error = format_str("Unknown event %s", name);
 			return 0;
 		}
 		return code;
@@ -1299,13 +1295,8 @@ uint32_t get_mouse_bindcode(const char *name, char **error) {
 	}
 	const char *event = libevdev_event_code_get_name(EV_KEY, code);
 	if (!event || strncmp(event, "BTN_", strlen("BTN_")) != 0) {
-		size_t len = snprintf(NULL, 0, "Event code %d (%s) is not a button",
-				code, event ? event : "(null)") + 1;
-		*error = malloc(len);
-		if (*error) {
-			snprintf(*error, len, "Event code %d (%s) is not a button",
-					code, event ? event : "(null)");
-		}
+		*error = format_str("Event code %d (%s) is not a button",
+			code, event ? event : "(null)");
 		return 0;
 	}
 	return code;
diff --git a/sway/input/input-manager.c b/sway/input/input-manager.c
index ea2cc0381..1115ba5ec 100644
--- a/sway/input/input-manager.c
+++ b/sway/input/input-manager.c
@@ -80,15 +80,7 @@ char *input_device_get_identifier(struct wlr_input_device *device) {
 		}
 	}
 
-	const char *fmt = "%d:%d:%s";
-	int len = snprintf(NULL, 0, fmt, vendor, product, name) + 1;
-	char *identifier = malloc(len);
-	if (!identifier) {
-		sway_log(SWAY_ERROR, "Unable to allocate unique input device name");
-		return NULL;
-	}
-
-	snprintf(identifier, len, fmt, vendor, product, name);
+	char *identifier = format_str("%d:%d:%s", vendor, product, name);
 	free(name);
 	return identifier;
 }
diff --git a/sway/input/keyboard.c b/sway/input/keyboard.c
index 45a588ecb..c3bf4fbbd 100644
--- a/sway/input/keyboard.c
+++ b/sway/input/keyboard.c
@@ -717,23 +717,11 @@ struct sway_keyboard *sway_keyboard_create(struct sway_seat *seat,
 
 static void handle_xkb_context_log(struct xkb_context *context,
 		enum xkb_log_level level, const char *format, va_list args) {
-	va_list args_copy;
-	va_copy(args_copy, args);
-	size_t length = vsnprintf(NULL, 0, format, args_copy) + 1;
-	va_end(args_copy);
+	char *error = vformat_str(format, args);
 
-	char *error = malloc(length);
-	if (!error) {
-		sway_log(SWAY_ERROR, "Failed to allocate libxkbcommon log message");
-		return;
-	}
-
-	va_copy(args_copy, args);
-	vsnprintf(error, length, format, args_copy);
-	va_end(args_copy);
-
-	if (error[length - 2] == '\n') {
-		error[length - 2] = '\0';
+	size_t len = strlen(error);
+	if (error[len - 1] == '\n') {
+		error[len - 1] = '\0';
 	}
 
 	sway_log_importance_t importance = SWAY_DEBUG;
@@ -768,13 +756,8 @@ struct xkb_keymap *sway_keyboard_compile_keymap(struct input_config *ic,
 		if (!keymap_file) {
 			sway_log_errno(SWAY_ERROR, "cannot read xkb file %s", ic->xkb_file);
 			if (error) {
-				size_t len = snprintf(NULL, 0, "cannot read xkb file %s: %s",
-						ic->xkb_file, strerror(errno)) + 1;
-				*error = malloc(len);
-				if (*error) {
-					snprintf(*error, len, "cannot read xkb_file %s: %s",
-							ic->xkb_file, strerror(errno));
-				}
+				*error = format_str("cannot read xkb file %s: %s",
+					ic->xkb_file, strerror(errno));
 			}
 			goto cleanup;
 		}
diff --git a/sway/swaynag.c b/sway/swaynag.c
index 4a0a6d305..6031174d2 100644
--- a/sway/swaynag.c
+++ b/sway/swaynag.c
@@ -145,22 +145,16 @@ void swaynag_log(const char *swaynag_command, struct swaynag_instance *swaynag,
 
 	va_list args;
 	va_start(args, fmt);
-	size_t length = vsnprintf(NULL, 0, fmt, args) + 1;
+	char *str = vformat_str(fmt, args);
 	va_end(args);
-
-	char *temp = malloc(length + 1);
-	if (!temp) {
+	if (!str) {
 		sway_log(SWAY_ERROR, "Failed to allocate buffer for swaynag log entry.");
 		return;
 	}
 
-	va_start(args, fmt);
-	vsnprintf(temp, length, fmt, args);
-	va_end(args);
+	write(swaynag->fd[1], str, strlen(str));
 
-	write(swaynag->fd[1], temp, length);
-
-	free(temp);
+	free(str);
 }
 
 void swaynag_show(struct swaynag_instance *swaynag) {
diff --git a/swaybar/tray/host.c b/swaybar/tray/host.c
index ddf2416d6..eea2caa59 100644
--- a/swaybar/tray/host.c
+++ b/swaybar/tray/host.c
@@ -10,6 +10,7 @@
 #include "swaybar/tray/tray.h"
 #include "list.h"
 #include "log.h"
+#include "stringop.h"
 
 static const char *watcher_path = "/StatusNotifierWatcher";
 
@@ -138,12 +139,10 @@ static int handle_new_watcher(sd_bus_message *msg,
 
 bool init_host(struct swaybar_host *host, char *protocol,
 		struct swaybar_tray *tray) {
-	size_t len = snprintf(NULL, 0, "org.%s.StatusNotifierWatcher", protocol) + 1;
-	host->watcher_interface = malloc(len);
+	host->watcher_interface = format_str("org.%s.StatusNotifierWatcher", protocol);
 	if (!host->watcher_interface) {
 		return false;
 	}
-	snprintf(host->watcher_interface, len, "org.%s.StatusNotifierWatcher", protocol);
 
 	sd_bus_slot *reg_slot = NULL, *unreg_slot = NULL, *watcher_slot = NULL;
 	int ret = sd_bus_match_signal(tray->bus, &reg_slot, host->watcher_interface,
@@ -173,13 +172,10 @@ bool init_host(struct swaybar_host *host, char *protocol,
 	}
 
 	pid_t pid = getpid();
-	size_t service_len = snprintf(NULL, 0, "org.%s.StatusNotifierHost-%d",
-			protocol, pid) + 1;
-	host->service = malloc(service_len);
+	host->service = format_str("org.%s.StatusNotifierHost-%d", protocol, pid);
 	if (!host->service) {
 		goto error;
 	}
-	snprintf(host->service, service_len, "org.%s.StatusNotifierHost-%d", protocol, pid);
 	ret = sd_bus_request_name(tray->bus, host->service, 0);
 	if (ret < 0) {
 		sway_log(SWAY_DEBUG, "Failed to acquire service name: %s", strerror(-ret));
diff --git a/swaybar/tray/icon.c b/swaybar/tray/icon.c
index c426c3d4a..b513dca55 100644
--- a/swaybar/tray/icon.c
+++ b/swaybar/tray/icon.c
@@ -40,9 +40,7 @@ static list_t *get_basedirs(void) {
 	data_dirs = strdup(data_dirs);
 	char *dir = strtok(data_dirs, ":");
 	do {
-		size_t path_len = snprintf(NULL, 0, "%s/icons", dir) + 1;
-		char *path = malloc(path_len);
-		snprintf(path, path_len, "%s/icons", dir);
+		char *path = format_str("%s/icons", dir);
 		list_add(basedirs, path);
 	} while ((dir = strtok(NULL, ":")));
 	free(data_dirs);
@@ -206,13 +204,7 @@ static const char *entry_handler(char *group, char *key, char *value,
  */
 static struct icon_theme *read_theme_file(char *basedir, char *theme_name) {
 	// look for index.theme file
-	size_t path_len = snprintf(NULL, 0, "%s/%s/index.theme", basedir,
-			theme_name) + 1;
-	char *path = malloc(path_len);
-	if (!path) {
-		return NULL;
-	}
-	snprintf(path, path_len, "%s/%s/index.theme", basedir, theme_name);
+	char *path = format_str("%s/%s/index.theme", basedir, theme_name);
 	FILE *theme_file = fopen(path, "r");
 	free(path);
 	if (!theme_file) {
@@ -416,26 +408,20 @@ static char *find_icon_in_subdir(char *name, char *basedir, char *theme,
 #endif
 	};
 
-	size_t path_len = snprintf(NULL, 0, "%s/%s/%s/%s.EXT", basedir, theme,
-			subdir, name) + 1;
-	char *path = malloc(path_len);
-
 	for (size_t i = 0; i < sizeof(extensions) / sizeof(*extensions); ++i) {
-		snprintf(path, path_len, "%s/%s/%s/%s.%s", basedir, theme, subdir,
-				name, extensions[i]);
+		char *path = format_str("%s/%s/%s/%s.%s",
+			basedir, theme, subdir, name, extensions[i]);
 		if (access(path, R_OK) == 0) {
 			return path;
 		}
+		free(path);
 	}
 
-	free(path);
 	return NULL;
 }
 
 static bool theme_exists_in_basedir(char *theme, char *basedir) {
-	size_t path_len = snprintf(NULL, 0, "%s/%s", basedir, theme) + 1;
-	char *path = malloc(path_len);
-	snprintf(path, path_len, "%s/%s", basedir, theme);
+	char *path = format_str("%s/%s", basedir, theme);
 	bool ret = dir_exists(path);
 	free(path);
 	return ret;
diff --git a/swaybar/tray/watcher.c b/swaybar/tray/watcher.c
index 16afc27ce..551e1d12c 100644
--- a/swaybar/tray/watcher.c
+++ b/swaybar/tray/watcher.c
@@ -6,6 +6,7 @@
 #include <string.h>
 #include "list.h"
 #include "log.h"
+#include "stringop.h"
 #include "swaybar/tray/watcher.h"
 
 static const char *obj_path = "/StatusNotifierWatcher";
@@ -76,9 +77,7 @@ static int register_sni(sd_bus_message *msg, void *data, sd_bus_error *error) {
 			service = service_or_path;
 			path = "/StatusNotifierItem";
 		}
-		size_t id_len = snprintf(NULL, 0, "%s%s", service, path) + 1;
-		id = malloc(id_len);
-		snprintf(id, id_len, "%s%s", service, path);
+		id = format_str("%s%s", service, path);
 	}
 
 	if (list_seq_find(watcher->items, cmp_id, id) == -1) {
@@ -159,9 +158,7 @@ struct swaybar_watcher *create_watcher(char *protocol, sd_bus *bus) {
 		return NULL;
 	}
 
-	size_t len = snprintf(NULL, 0, "org.%s.StatusNotifierWatcher", protocol) + 1;
-	watcher->interface = malloc(len);
-	snprintf(watcher->interface, len, "org.%s.StatusNotifierWatcher", protocol);
+	watcher->interface = format_str("org.%s.StatusNotifierWatcher", protocol);
 
 	sd_bus_slot *signal_slot = NULL, *vtable_slot = NULL;
 	int ret = sd_bus_add_object_vtable(bus, &vtable_slot, obj_path,