diff --git a/CMakeLists.txt b/CMakeLists.txt
index ea40029..533a34e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -27,6 +27,7 @@ pkg_check_modules(ALSA REQUIRED alsa)                               # Module/als
 add_executable(f00bar
   bar.c bar.h
   config.c config.h
+  config-verify.c config-verify.h
   decoration.h
   font.c font.h
   log.c log.h
diff --git a/config-verify.c b/config-verify.c
new file mode 100644
index 0000000..15e0a3a
--- /dev/null
+++ b/config-verify.c
@@ -0,0 +1,762 @@
+#include "config-verify.h"
+
+#include <string.h>
+#include <assert.h>
+
+#define LOG_MODULE "config:verify"
+#define LOG_ENABLE_DBG 0
+#include "log.h"
+#include "tllist.h"
+
+typedef tll(const char *) keychain_t;
+
+static keychain_t *
+chain_push(keychain_t *chain, const char *key)
+{
+    tll_push_back(*chain, key);
+    return chain;
+}
+
+static void
+chain_pop(keychain_t *chain)
+{
+    tll_pop_back(*chain);
+}
+
+static const char *
+err_prefix(const keychain_t *chain, const struct yml_node *node)
+{
+    static char msg[4096];
+    int idx = 0;
+
+    tll_foreach(*chain, key)
+        idx += snprintf(&msg[idx], sizeof(msg) - idx, "%s.", key->item);
+
+    /* Remove trailing "." */
+    msg[idx - 1] = '\0';
+    return msg;
+}
+
+static bool
+verify_string(keychain_t *chain, const struct yml_node *node)
+{
+    const char *s = yml_value_as_string(node);
+    if (s == NULL) {
+        LOG_ERR("%s: value must be a string", err_prefix(chain, node));
+        return false;
+    }
+
+    return true;
+}
+
+static bool
+verify_int(keychain_t *chain, const struct yml_node *node)
+{
+    if (yml_value_is_int(node))
+        return true;
+
+    LOG_ERR("%s: value is not an integer: '%s'",
+            err_prefix(chain, node), yml_value_as_string(node));
+    return false;
+}
+
+static bool
+verify_enum(keychain_t *chain, const struct yml_node *node,
+            const char *values[], size_t count)
+{
+    const char *s = yml_value_as_string(node);
+    if (s == NULL) {
+        LOG_ERR("%s: value must be a string", err_prefix(chain, node));
+        return false;
+    }
+
+    for (size_t i = 0; s != NULL && i < count; i++) {
+        if (strcmp(s, values[i]) == 0)
+            return true;
+    }
+
+    LOG_ERR("%s: value must be one of:", err_prefix(chain, node));
+    for (size_t i = 0; i < count; i++)
+        LOG_ERR("  %s", values[i]);
+
+    return false;
+}
+
+static bool
+verify_color(keychain_t *chain, const struct yml_node *node)
+{
+    const char *s = yml_value_as_string(node);
+    if (s == NULL) {
+        LOG_ERR("%s: value must be a string", err_prefix(chain, node));
+        return false;
+    }
+
+    unsigned int r, g, b, a;
+    int v = sscanf(s, "%02x%02x%02x%02x", &r, &g, &b, &a);
+
+    if (strlen(s) != 8 || v != 4) {
+        LOG_ERR("%s: value must be a color ('rrggbbaa', e.g ff00ffff)",
+                err_prefix(chain, node));
+        return false;
+    }
+
+    return true;
+}
+
+static bool
+verify_font(keychain_t *chain, const struct yml_node *node)
+{
+    if (!yml_is_dict(node)) {
+        LOG_ERR("%s: must be a dictionary", err_prefix(chain, node));
+        return false;
+    }
+
+    for (struct yml_dict_iter it = yml_dict_iter(node);
+         it.key != NULL;
+         yml_dict_next(&it))
+    {
+        const char *sub_key = yml_value_as_string(it.key);
+        if (sub_key == NULL) {
+            LOG_ERR("%s: font: key must be a string", err_prefix(chain, node));
+            return false;
+        }
+
+        if (strcmp(sub_key, "size") == 0 ||
+            strcmp(sub_key, "y_offset") == 0)
+        {
+            if (!verify_int(chain_push(chain, sub_key), it.value))
+                return false;
+        } else if (strcmp(sub_key, "family") == 0) {
+            if (!verify_string(chain_push(chain, sub_key), it.value))
+                return false;
+        } else {
+            LOG_ERR("%s: font: invalid key: %s", err_prefix(chain, node), sub_key);
+            return false;
+        }
+
+        chain_pop(chain);
+    }
+
+    return true;
+}
+
+static bool
+verify_border(keychain_t *chain, const struct yml_node *node)
+{
+    if (!yml_is_dict(node)) {
+        LOG_ERR("bar: border: must be a dictionary");
+        return false;
+    }
+
+    for (struct yml_dict_iter it = yml_dict_iter(node);
+         it.key != NULL;
+         yml_dict_next(&it))
+    {
+        const char *key = yml_value_as_string(it.key);
+        if (key == NULL) {
+            LOG_ERR("%s: key must be a string", err_prefix(chain, node));
+            return false;
+        }
+
+        if (strcmp(key, "width") == 0) {
+            if (!verify_int(chain_push(chain, key), it.value))
+                return false;
+        } else if (strcmp(key, "color") == 0) {
+            if (!verify_color(chain_push(chain, key), it.value))
+                return false;
+        } else {
+            LOG_ERR("%s: invalid key: %s", err_prefix(chain, node), key);
+            return false;
+        }
+
+        chain_pop(chain);
+    }
+
+    return true;
+}
+
+static bool
+verify_particle(keychain_t *chain, const struct yml_node *node)
+{
+    return true;
+}
+
+static bool
+verify_module_alsa(keychain_t *chain, const struct yml_node *node)
+{
+    for (struct yml_dict_iter it = yml_dict_iter(node);
+         it.key != NULL;
+         yml_dict_next(&it))
+    {
+        const char *key = yml_value_as_string(it.key);
+        if (key == NULL) {
+            LOG_ERR("%s: key must be a string", err_prefix(chain, node));
+            return false;
+        }
+
+        if (strcmp(key, "card") == 0 ||
+            strcmp(key, "mixer") == 0)
+        {
+            if (!verify_string(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "content") == 0) {
+            if (!verify_particle(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "anchors") == 0) {
+            /* Skip */
+            chain_push(chain, key);
+        }
+
+        else {
+            LOG_ERR("%s: invalid key: %s", err_prefix(chain, node), key);
+            return false;
+        }
+
+        chain_pop(chain);
+    }
+
+    return true;
+}
+
+static bool
+verify_module_backlight(keychain_t *chain, const struct yml_node *node)
+{
+    for (struct yml_dict_iter it = yml_dict_iter(node);
+         it.key != NULL;
+         yml_dict_next(&it))
+    {
+        const char *key = yml_value_as_string(it.key);
+        if (key == NULL) {
+            LOG_ERR("%s: key must be a string", err_prefix(chain, node));
+            return false;
+        }
+
+        if (strcmp(key, "name") == 0) {
+            if (!verify_string(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "content") == 0) {
+            if (!verify_particle(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "anchors") == 0) {
+            /* Skip */
+            chain_push(chain, key);
+        }
+
+        else {
+            LOG_ERR("%s: invalid key: %s", err_prefix(chain, node), key);
+            return false;
+        }
+
+        chain_pop(chain);
+    }
+
+    return true;
+}
+
+static bool
+verify_module_battery(keychain_t *chain, const struct yml_node *node)
+{
+    for (struct yml_dict_iter it = yml_dict_iter(node);
+         it.key != NULL;
+         yml_dict_next(&it))
+    {
+        const char *key = yml_value_as_string(it.key);
+        if (key == NULL) {
+            LOG_ERR("%s: key must be a string", err_prefix(chain, node));
+            return false;
+        }
+
+        if (strcmp(key, "name") == 0) {
+            if (!verify_string(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "poll_interval") == 0) {
+            if (!verify_int(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "content") == 0) {
+            if (!verify_particle(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "anchors") == 0) {
+            /* Skip */
+            chain_push(chain, key);
+        }
+
+        else {
+            LOG_ERR("%s: invalid key: %s", err_prefix(chain, node), key);
+            return false;
+        }
+
+        chain_pop(chain);
+    }
+
+    return true;
+}
+
+static bool
+verify_module_clock(keychain_t *chain, const struct yml_node *node)
+{
+    for (struct yml_dict_iter it = yml_dict_iter(node);
+         it.key != NULL;
+         yml_dict_next(&it))
+    {
+        const char *key = yml_value_as_string(it.key);
+        if (key == NULL) {
+            LOG_ERR("%s: key must be a string", err_prefix(chain, node));
+            return false;
+        }
+
+        if (strcmp(key, "content") == 0) {
+            if (!verify_particle(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "anchors") == 0) {
+            /* Skip */
+            chain_push(chain, key);
+        }
+
+        else {
+            LOG_ERR("%s: invalid key: %s", err_prefix(chain, node), key);
+            return false;
+        }
+
+        chain_pop(chain);
+    }
+
+    return true;
+}
+
+static bool
+verify_module_i3(keychain_t *chain, const struct yml_node *node)
+{
+    for (struct yml_dict_iter it = yml_dict_iter(node);
+         it.key != NULL;
+         yml_dict_next(&it))
+    {
+        const char *key = yml_value_as_string(it.key);
+        if (key == NULL) {
+            LOG_ERR("%s: key must be a string", err_prefix(chain, node));
+            return false;
+        }
+
+        if (strcmp(key, "spacing") == 0 ||
+            strcmp(key, "left_spacing") == 0 ||
+            strcmp(key, "right_spacing") == 0)
+        {
+            if (!verify_int(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "content") == 0) {
+            if (!verify_particle(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "anchors") == 0) {
+            /* Skip */
+            chain_push(chain, key);
+        }
+
+        else {
+            LOG_ERR("%s: invalid key: %s", err_prefix(chain, node), key);
+            return false;
+        }
+
+        chain_pop(chain);
+    }
+
+    return true;
+}
+
+static bool
+verify_module_label(keychain_t *chain, const struct yml_node *node)
+{
+    for (struct yml_dict_iter it = yml_dict_iter(node);
+         it.key != NULL;
+         yml_dict_next(&it))
+    {
+        const char *key = yml_value_as_string(it.key);
+        if (key == NULL) {
+            LOG_ERR("%s: key must be a string", err_prefix(chain, node));
+            return false;
+        }
+
+        if (strcmp(key, "content") == 0) {
+            if (!verify_particle(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "anchors") == 0) {
+            /* Skip */
+            chain_push(chain, key);
+        }
+
+        else {
+            LOG_ERR("%s: invalid key: %s", err_prefix(chain, node), key);
+            return false;
+        }
+
+        chain_pop(chain);
+    }
+
+    return true;
+}
+
+static bool
+verify_module_mpd(keychain_t *chain, const struct yml_node *node)
+{
+    for (struct yml_dict_iter it = yml_dict_iter(node);
+         it.key != NULL;
+         yml_dict_next(&it))
+    {
+        const char *key = yml_value_as_string(it.key);
+        if (key == NULL) {
+            LOG_ERR("%s: key must be a string", err_prefix(chain, node));
+            return false;
+        }
+
+        if (strcmp(key, "host") == 0) {
+            if (!verify_string(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "port") == 0) {
+            if (!verify_int(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "content") == 0) {
+            if (!verify_particle(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "anchors") == 0) {
+            /* Skip */
+            chain_push(chain, key);
+        }
+
+        else {
+            LOG_ERR("%s: invalid key: %s", err_prefix(chain, node), key);
+            return false;
+        }
+
+        chain_pop(chain);
+    }
+
+    return true;
+}
+
+static bool
+verify_module_network(keychain_t *chain, const struct yml_node *node)
+{
+    for (struct yml_dict_iter it = yml_dict_iter(node);
+         it.key != NULL;
+         yml_dict_next(&it))
+    {
+        const char *key = yml_value_as_string(it.key);
+        if (key == NULL) {
+            LOG_ERR("%s: key must be a string", err_prefix(chain, node));
+            return false;
+        }
+
+        if (strcmp(key, "name") == 0) {
+            if (!verify_string(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "content") == 0) {
+            if (!verify_particle(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "anchors") == 0) {
+            /* Skip */
+            chain_push(chain, key);
+        }
+
+        else {
+            LOG_ERR("%s: invalid key: %s", err_prefix(chain, node), key);
+            return false;
+        }
+
+        chain_pop(chain);
+    }
+
+    return true;
+}
+
+static bool
+verify_module_removables(keychain_t *chain, const struct yml_node *node)
+{
+    for (struct yml_dict_iter it = yml_dict_iter(node);
+         it.key != NULL;
+         yml_dict_next(&it))
+    {
+        const char *key = yml_value_as_string(it.key);
+        if (key == NULL) {
+            LOG_ERR("%s: key must be a string", err_prefix(chain, node));
+            return false;
+        }
+
+        if (strcmp(key, "spacing") == 0  ||
+            strcmp(key, "left_spacing") == 0 ||
+            strcmp(key, "right_spacing") == 0)
+        {
+            if (!verify_int(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "content") == 0) {
+            if (!verify_particle(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "anchors") == 0) {
+            /* Skip */
+            chain_push(chain, key);
+        }
+
+        else {
+            LOG_ERR("%s: invalid key: %s", err_prefix(chain, node), key);
+            return false;
+        }
+
+        chain_pop(chain);
+    }
+
+    return true;
+}
+
+static bool
+verify_module_xkb(keychain_t *chain, const struct yml_node *node)
+{
+    for (struct yml_dict_iter it = yml_dict_iter(node);
+         it.key != NULL;
+         yml_dict_next(&it))
+    {
+        const char *key = yml_value_as_string(it.key);
+        if (key == NULL) {
+            LOG_ERR("%s: key must be a string", err_prefix(chain, node));
+            return false;
+        }
+
+        if (strcmp(key, "content") == 0) {
+            if (!verify_particle(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "anchors") == 0) {
+            /* Skip */
+            chain_push(chain, key);
+        }
+
+        else {
+            LOG_ERR("%s: invalid key: %s", err_prefix(chain, node), key);
+            return false;
+        }
+
+        chain_pop(chain);
+    }
+
+    return true;
+}
+
+static bool
+verify_module_xwindow(keychain_t *chain, const struct yml_node *node)
+{
+    for (struct yml_dict_iter it = yml_dict_iter(node);
+         it.key != NULL;
+         yml_dict_next(&it))
+    {
+        const char *key = yml_value_as_string(it.key);
+        if (key == NULL) {
+            LOG_ERR("%s: key must be a string", err_prefix(chain, node));
+            return false;
+        }
+
+        if (strcmp(key, "content") == 0) {
+            if (!verify_particle(chain_push(chain, key), it.value))
+                return false;
+        }
+
+        else if (strcmp(key, "anchors") == 0) {
+            /* Skip */
+            chain_push(chain, key);
+        }
+
+        else {
+            LOG_ERR("%s: invalid key: %s", err_prefix(chain, node), key);
+            return false;
+        }
+
+        chain_pop(chain);
+    }
+
+    return true;
+}
+
+static bool
+verify_module(keychain_t *chain, const struct yml_node *node)
+{
+    if (!yml_is_dict(node) || yml_dict_length(node) != 1) {
+        LOG_ERR("%s: module must be a dictionary with a single key; "
+                "the name of the module", err_prefix(chain, node));
+        return false;
+    }
+
+    struct yml_dict_iter m = yml_dict_iter(node);
+    const struct yml_node *module = m.key;
+    const struct yml_node *values = m.value;
+
+    const char *mod_name = yml_value_as_string(module);
+    if (mod_name == NULL) {
+        LOG_ERR("%s: module name must be a string", err_prefix(chain, node));
+        return false;
+    }
+
+    static const struct {
+        const char *name;
+        bool (*verify_fun)(keychain_t *chain, const struct yml_node *node);
+    } modules[] = {
+        {"alsa", &verify_module_alsa},
+        {"backlight", &verify_module_backlight},
+        {"battery", &verify_module_battery},
+        {"clock", &verify_module_clock},
+        {"i3", &verify_module_i3},
+        {"label", &verify_module_label},
+        {"mpd", &verify_module_mpd},
+        {"network", &verify_module_network},
+        {"removables", &verify_module_removables},
+        {"xkb", &verify_module_xkb},
+        {"xwindow", &verify_module_xwindow},
+    };
+
+    for (size_t i = 0; i < sizeof(modules) / sizeof(modules[0]); i++) {
+        if (strcmp(mod_name, modules[i].name) == 0) {
+            if (!modules[i].verify_fun(chain_push(chain, mod_name), values))
+                return false;
+            chain_pop(chain);
+            return true;
+        }
+    }
+
+    LOG_ERR("%s: invalid module name: %s", err_prefix(chain, node), mod_name);
+    return false;
+}
+
+static bool
+verify_module_list(keychain_t *chain, const struct yml_node *node)
+{
+    if (!yml_is_list(node)) {
+        LOG_ERR("%s: must be a list of modules", err_prefix(chain, node));
+        return false;
+    }
+
+    for (struct yml_list_iter it = yml_list_iter(node);
+         it.node != NULL;
+         yml_list_next(&it))
+    {
+        if (!verify_module(chain, it.node))
+            return false;
+    }
+
+    return true;
+}
+
+bool
+config_verify_bar(const struct yml_node *bar)
+{
+    if (!yml_is_dict(bar)) {
+        LOG_ERR("bar is not a dictionary");
+        return false;
+    }
+
+    keychain_t chain = tll_init();
+    chain_push(&chain, "bar");
+
+    bool ret = false;
+
+    for (struct yml_dict_iter it = yml_dict_iter(bar);
+         it.key != NULL;
+         yml_dict_next(&it))
+    {
+        if (!yml_is_scalar(it.key)) {
+            LOG_ERR("bar: key is not a scalar");
+            goto err;
+        }
+
+        const char *key = yml_value_as_string(it.key);
+        if (key == NULL) {
+            LOG_ERR("bar: key must be a string");
+            goto err;
+        }
+
+        if (strcmp(key, "height") == 0 ||
+            strcmp(key, "spacing") == 0 ||
+            strcmp(key, "left_spacing") == 0 ||
+            strcmp(key, "right_spacing") == 0 ||
+            strcmp(key, "margin") == 0 ||
+            strcmp(key, "left_margin") == 0 ||
+            strcmp(key, "right_margin") == 0)
+        {
+            if (!verify_int(chain_push(&chain, key), it.value))
+                goto err;
+        }
+
+        else if (strcmp(key, "location") == 0) {
+            if (!verify_enum(chain_push(&chain, key), it.value,
+                             (const char *[]){"top", "bottom"}, 2))
+                goto err;
+        }
+
+        else if (strcmp(key, "background") == 0) {
+            if (!verify_color(chain_push(&chain, key), it.value))
+                goto err;
+        }
+
+        else if (strcmp(key, "border") == 0) {
+            if (!verify_border(chain_push(&chain, key), it.value))
+                goto err;
+        }
+
+        else if (strcmp(key, "font") == 0) {
+            if (!verify_font(chain_push(&chain, key), it.value))
+                goto err;
+        }
+
+        else if (strcmp(key, "left") == 0 ||
+                 strcmp(key, "center") == 0 ||
+                 strcmp(key, "right") == 0)
+        {
+            if (!verify_module_list(chain_push(&chain, key), it.value))
+                goto err;
+        }
+
+        else {
+            LOG_ERR("%s: invalid key: %s", err_prefix(&chain, bar), key);
+            goto err;
+        }
+
+        LOG_DBG("%s: verified", key);
+        chain_pop(&chain);
+    }
+
+    ret = true;
+
+err:
+    tll_free(chain);
+    return ret;
+}
diff --git a/config-verify.h b/config-verify.h
new file mode 100644
index 0000000..92b3941
--- /dev/null
+++ b/config-verify.h
@@ -0,0 +1,5 @@
+#pragma once
+#include <stdbool.h>
+#include "yml.h"
+
+bool config_verify_bar(const struct yml_node *bar);
diff --git a/config.c b/config.c
index c46539d..c4568cd 100644
--- a/config.c
+++ b/config.c
@@ -33,6 +33,8 @@
 #include "modules/xkb.h"
 #include "modules/xwindow.h"
 
+#include "config-verify.h"
+
 static uint8_t
 hex_nibble(char hex)
 {
@@ -590,6 +592,9 @@ module_alsa_from_config(const struct yml_node *node,
 struct bar *
 conf_to_bar(const struct yml_node *bar)
 {
+    if (!config_verify_bar(bar))
+        return NULL;
+
     struct bar_config conf = {0};
 
     /* Create a default font */
@@ -676,33 +681,36 @@ conf_to_bar(const struct yml_node *bar)
                  it.node != NULL;
                  yml_list_next(&it), idx++)
             {
-                const struct yml_node *n = yml_get_value(it.node, "module");
+                assert(yml_is_dict(it.node));
+                assert(yml_dict_length(it.node) == 1);
 
-                assert(n != NULL);
-                const char *mod_name = yml_value_as_string(n);
+                struct yml_dict_iter m = yml_dict_iter(it.node);
+
+                const char *mod_name = yml_value_as_string(m.key);
+                assert(mod_name != NULL);
 
                 if (strcmp(mod_name, "label") == 0)
-                    mods[idx] = module_label_from_config(it.node, font);
+                    mods[idx] = module_label_from_config(m.value, font);
                 else if (strcmp(mod_name, "clock") == 0)
-                    mods[idx] = module_clock_from_config(it.node, font);
+                    mods[idx] = module_clock_from_config(m.value, font);
                 else if (strcmp(mod_name, "xwindow") == 0)
-                    mods[idx] = module_xwindow_from_config(it.node, font);
+                    mods[idx] = module_xwindow_from_config(m.value, font);
                 else if (strcmp(mod_name, "i3") == 0)
-                    mods[idx] = module_i3_from_config(it.node, font);
+                    mods[idx] = module_i3_from_config(m.value, font);
                 else if (strcmp(mod_name, "battery") == 0)
-                    mods[idx] = module_battery_from_config(it.node, font);
+                    mods[idx] = module_battery_from_config(m.value, font);
                 else if (strcmp(mod_name, "xkb") == 0)
-                    mods[idx] = module_xkb_from_config(it.node, font);
+                    mods[idx] = module_xkb_from_config(m.value, font);
                 else if (strcmp(mod_name, "backlight") == 0)
-                    mods[idx] = module_backlight_from_config(it.node, font);
+                    mods[idx] = module_backlight_from_config(m.value, font);
                 else if (strcmp(mod_name, "mpd") == 0)
-                    mods[idx] = module_mpd_from_config(it.node, font);
+                    mods[idx] = module_mpd_from_config(m.value, font);
                 else if (strcmp(mod_name, "network") == 0)
-                    mods[idx] = module_network_from_config(it.node, font);
+                    mods[idx] = module_network_from_config(m.value, font);
                 else if (strcmp(mod_name, "removables") == 0)
-                    mods[idx] = module_removables_from_config(it.node, font);
+                    mods[idx] = module_removables_from_config(m.value, font);
                 else if (strcmp(mod_name, "alsa") == 0)
-                    mods[idx] = module_alsa_from_config(it.node, font);
+                    mods[idx] = module_alsa_from_config(m.value, font);
                 else
                     assert(false);
             }
diff --git a/main.c b/main.c
index 3507c42..f9164d7 100644
--- a/main.c
+++ b/main.c
@@ -82,7 +82,12 @@ main(int argc, const char *const *argv)
         return 1;
     }
 
-    free(config_path);
+    const struct yml_node *bar_conf = yml_get_value(conf, "bar");
+    if (bar_conf == NULL) {
+        LOG_ERR("%s: missing required top level key 'bar'", config_path);
+        free(config_path);
+        return 1;
+    }
 
     xcb_init();
 
@@ -92,10 +97,18 @@ main(int argc, const char *const *argv)
     int abort_fd = eventfd(0, EFD_CLOEXEC);
     if (abort_fd == -1) {
         LOG_ERRNO("failed to create eventfd (for abort signalling)");
+        free(config_path);
         return 1;
     }
 
-    struct bar *bar = conf_to_bar(yml_get_value(conf, "bar"));
+    struct bar *bar = conf_to_bar(bar_conf);
+    if (bar == NULL) {
+        LOG_ERR("%s: failed to load configuration", config_path);
+        free(config_path);
+        return 1;
+    }
+
+    free(config_path);
 
     struct bar_run_context bar_ctx = {
         .bar = bar,
diff --git a/yml.c b/yml.c
index bfed04f..6de573b 100644
--- a/yml.c
+++ b/yml.c
@@ -682,42 +682,79 @@ yml_dict_length(const struct yml_node *dict)
 const char *
 yml_value_as_string(const struct yml_node *value)
 {
-    assert(yml_is_scalar(value));
+    if (!yml_is_scalar(value))
+        return NULL;
     return value->scalar.value;
 }
 
+static bool
+_as_int(const struct yml_node *value, long *ret)
+{
+    const char *s = yml_value_as_string(value);
+    if (s == NULL)
+        return false;
+
+    int cnt;
+    int res = sscanf(s, "%ld%n", ret, &cnt);
+    return res == 1 && strlen(s) == (size_t)cnt;
+}
+
+bool
+yml_value_is_int(const struct yml_node *value)
+{
+    long dummy;
+    return _as_int(value, &dummy);
+}
+
 long
 yml_value_as_int(const struct yml_node *value)
 {
-    assert(yml_is_scalar(value));
-
-    long ival;
-    int res = sscanf(yml_value_as_string(value), "%ld", &ival);
-    return res != 1 ? -1 : ival;
+    long ret = -1;
+    _as_int(value, &ret);
+    return ret;
 }
 
-bool
-yml_value_as_bool(const struct yml_node *value)
+static bool
+_as_bool(const struct yml_node *value, bool *ret)
 {
+    if (!yml_is_scalar(value))
+        return false;
+
     const char *v = yml_value_as_string(value);
     if (strcasecmp(v, "y") == 0 ||
         strcasecmp(v, "yes") == 0 ||
         strcasecmp(v, "true") == 0 ||
         strcasecmp(v, "on") == 0)
     {
+        *ret = true;
         return true;
     } else if (strcasecmp(v, "n") == 0 ||
                strcasecmp(v, "no") == 0 ||
                strcasecmp(v, "false") == 0 ||
                strcasecmp(v, "off") == 0)
     {
-        return false;
-    } else
-        assert(false);
+        *ret = false;
+        return true;
+    }
 
     return false;
 }
 
+bool
+yml_value_is_bool(const struct yml_node *value)
+{
+    bool dummy;
+    return _as_bool(value, &dummy);
+}
+
+bool
+yml_value_as_bool(const struct yml_node *value)
+{
+    bool ret;
+    _as_bool(value, &ret);
+    return ret;
+}
+
 static void
 _print_node(const struct yml_node *n, int indent)
 {
diff --git a/yml.h b/yml.h
index 51ec58c..489b73a 100644
--- a/yml.h
+++ b/yml.h
@@ -32,6 +32,9 @@ struct yml_dict_iter yml_dict_iter(const struct yml_node *dict);
 void yml_dict_next(struct yml_dict_iter *iter);
 size_t yml_dict_length(const struct yml_node *dict);
 
+bool yml_value_is_int(const struct yml_node *value);
+bool yml_value_is_bool(const struct yml_node *value);
+
 const char *yml_value_as_string(const struct yml_node *value);
 long yml_value_as_int(const struct yml_node *value);
 bool yml_value_as_bool(const struct yml_node *value);