diff --git a/include/applet/adguard.h b/include/applet/adguard.h
index 5c749c9..c904eb3 100644
--- a/include/applet/adguard.h
+++ b/include/applet/adguard.h
@@ -14,6 +14,7 @@ typedef struct {
 } adguard;
 
 adguard* adguard_init();
+void adguard_free(adguard *info);
 process* adguard_load(adguard *info, const char *dir);
 
 #endif
diff --git a/include/applet/dnsproxy.h b/include/applet/dnsproxy.h
index c8597de..68eb67c 100644
--- a/include/applet/dnsproxy.h
+++ b/include/applet/dnsproxy.h
@@ -16,6 +16,7 @@ typedef struct {
     char **primary;
 } dnsproxy;
 
+void dnsproxy_free(dnsproxy *info);
 dnsproxy* dnsproxy_init(uint16_t port);
 void dnsproxy_add_primary(dnsproxy *info, const char *server);
 void dnsproxy_add_fallback(dnsproxy *info, const char *server);
diff --git a/include/applet/overture.h b/include/applet/overture.h
index 1c4f046..476942a 100644
--- a/include/applet/overture.h
+++ b/include/applet/overture.h
@@ -20,6 +20,7 @@ typedef struct {
 } overture;
 
 overture* overture_init();
+void overture_free(overture *info);
 process* overture_load(overture *info, const char *file);
 
 #endif
diff --git a/include/common.h b/include/common.h
index 5f5db0d..9524aa6 100644
--- a/include/common.h
+++ b/include/common.h
@@ -62,4 +62,11 @@ char* to_json(const char *config_file);
 cJSON* json_field_get(cJSON *entry, const char *field);
 void json_field_replace(cJSON *entry, const char *field, cJSON *content);
 
+uint8_t json_bool_value(char *key, cJSON *json);
+uint32_t** json_uint32_list_value(char *key, cJSON *json, uint32_t **uint32_list);
+char** json_string_list_value(char *key, cJSON *json, char **string_list);
+char* json_string_value(char* key, cJSON *json);
+int json_int_value(char *key, cJSON *json);
+uint8_t is_json_suffix(const char *file_name);
+
 #endif
diff --git a/include/loader/config.h b/include/loader/config.h
index 347f06f..de1f2d0 100644
--- a/include/loader/config.h
+++ b/include/loader/config.h
@@ -1,7 +1,7 @@
 #ifndef _CONFIG_H_
 #define _CONFIG_H_
 
-#include "common.h"
+#include <stdint.h>
 
 typedef struct {
     uint16_t port;
diff --git a/include/loader/loader.h b/include/loader/loader.h
index 34dd326..d4c54db 100644
--- a/include/loader/loader.h
+++ b/include/loader/loader.h
@@ -1,14 +1,15 @@
 #ifndef _LOADER_H_
 #define _LOADER_H_
 
+#include "adguard.h"
 #include "dnsproxy.h"
 #include "overture.h"
 
-struct {
+extern struct {
     dnsproxy *domestic;
     dnsproxy *foreign;
     overture *diverter;
-    // adguard
+    adguard *filter;
 } loader;
 
 void load_config(const char *config_file);
diff --git a/src/applet/adguard.c b/src/applet/adguard.c
index 1c27f64..f17726c 100644
--- a/src/applet/adguard.c
+++ b/src/applet/adguard.c
@@ -7,9 +7,16 @@
 void adguard_dump(adguard *info);
 char *adguard_config(adguard *info, const char *raw_config);
 
-adguard* adguard_init() {
+void adguard_free(adguard *info) { // free adguard options
+    free(info->upstream);
+    free(info->username);
+    free(info->password);
+    free(info);
+}
+
+adguard* adguard_init() { // init adguard options
     adguard *info = (adguard *)malloc(sizeof(adguard));
-    char *port_str = uint32_to_string(DIVERTER_PORT);
+    char *port_str = uint32_to_string(DIVERTER_PORT); // diverter port in string
     info->debug = FALSE;
     info->dns_port = DNS_PORT;
     info->web_port = ADGUARD_PORT;
@@ -20,7 +27,7 @@ adguard* adguard_init() {
     return info;
 }
 
-void adguard_dump(adguard *info) { // show adguard info in debug log
+void adguard_dump(adguard *info) { // show adguard options in debug log
     log_debug("AdGuardHome debug -> %s", show_bool(info->debug));
     log_debug("AdGuardHome dns port -> %u", info->dns_port);
     log_debug("AdGuardHome web port -> %u", info->web_port);
@@ -35,7 +42,7 @@ char *adguard_config(adguard *info, const char *raw_config) { // modify adguard
         log_fatal("AdGuardHome configure error");
     }
 
-    cJSON *user_config = cJSON_CreateObject();
+    cJSON *user_config = cJSON_CreateObject(); // setting up username and password
     cJSON *users_config = cJSON_CreateArray();
     char *password = gen_bcrypt(info->password);
     cJSON_AddItemToObject(user_config, "name", cJSON_CreateString(info->username));
@@ -44,7 +51,7 @@ char *adguard_config(adguard *info, const char *raw_config) { // modify adguard
     json_field_replace(json, "users", users_config);
     free(password);
 
-    cJSON *dns = json_field_get(json, "dns");
+    cJSON *dns = json_field_get(json, "dns"); // setting up dns options
     cJSON *upstream = cJSON_CreateArray();
     cJSON_AddItemToArray(upstream, cJSON_CreateString(info->upstream));
     json_field_replace(dns, "port", cJSON_CreateNumber(info->dns_port));
@@ -53,12 +60,12 @@ char *adguard_config(adguard *info, const char *raw_config) { // modify adguard
     json_field_replace(dns, "upstream_dns_file", cJSON_CreateString(""));
     json_field_replace(dns, "bootstrap_dns", cJSON_CreateArray());
 
-    char *config = cJSON_Print(json);
+    char *config = cJSON_Print(json); // generate json string
     cJSON_free(json);
     return config;
 }
 
-process* adguard_load(adguard *info, const char *dir) {
+process* adguard_load(adguard *info, const char *dir) { // load adguard options
     adguard_dump(info);
     if (!check_port(info->dns_port)) { // invalid dns port
         log_fatal("Invalid dns port `%u`", info->dns_port);
@@ -67,7 +74,7 @@ process* adguard_load(adguard *info, const char *dir) {
         log_fatal("Invalid web port `%u`", info->web_port);
     }
 
-    create_folder(dir);
+    create_folder(dir); // ensure adguard work dir exist
     char *adguard_config_ret;
     char *adguard_config_file = string_join(dir, "AdGuardHome.yaml");
     char *adguard_config_raw = to_json(adguard_config_file);
@@ -81,12 +88,12 @@ process* adguard_load(adguard *info, const char *dir) {
     save_file(adguard_config_file, adguard_config_ret); // save modified configure
     free(adguard_config_file);
 
-    process *proc = process_init("AdGuardHome", ADGUARD_BIN);
+    process *proc = process_init("AdGuardHome", ADGUARD_BIN); // generate adguard command
     char *port_str = uint32_to_string(info->web_port);
-    process_add_arg(proc, "--no-check-update");
+    process_add_arg(proc, "--no-check-update"); // disable update check (invalid in docker)
     process_add_arg(proc, "--work-dir");
     process_add_arg(proc, dir);
-    process_add_arg(proc, "--port");
+    process_add_arg(proc, "--port"); // web server port
     process_add_arg(proc, port_str);
     if (info->debug) {
         process_add_arg(proc, "--verbose"); // adguard enable debug mode
diff --git a/src/applet/dnsproxy.c b/src/applet/dnsproxy.c
index d1cecd5..fc0d148 100644
--- a/src/applet/dnsproxy.c
+++ b/src/applet/dnsproxy.c
@@ -20,6 +20,13 @@ void dnsproxy_add_bootstrap(dnsproxy *info, const char *server) { // add bootstr
     info->bootstrap = string_list_append(info->bootstrap, server);
 }
 
+void dnsproxy_free(dnsproxy *info) { // free dnsproxy options
+    string_list_free(info->bootstrap);
+    string_list_free(info->fallback);
+    string_list_free(info->primary);
+    free(info);
+}
+
 dnsproxy* dnsproxy_init(uint16_t port) { // init dnsproxy options
     dnsproxy *info = (dnsproxy *)malloc(sizeof(dnsproxy));
     info->port = port;
@@ -34,7 +41,7 @@ dnsproxy* dnsproxy_init(uint16_t port) { // init dnsproxy options
     return info;
 }
 
-void dnsproxy_dump(const char *caption, dnsproxy *info) { // show dnsproxy info in debug log
+void dnsproxy_dump(const char *caption, dnsproxy *info) { // show dnsproxy options in debug log
     char *str_dump;
     log_debug("%s port -> %u", caption, info->port);
     log_debug("%s cache -> %u", caption, info->cache);
@@ -56,7 +63,7 @@ void dnsproxy_dump(const char *caption, dnsproxy *info) { // show dnsproxy info
     free(str_dump);
 }
 
-process* dnsproxy_load(const char *caption, dnsproxy *info, const char *file) {
+process* dnsproxy_load(const char *caption, dnsproxy *info, const char *file) { // load dnsproxy options
     dnsproxy_dump(caption, info);
     if (!check_port(info->port)) { // invalid server port
         log_fatal("Invalid port `%u`", info->port);
@@ -65,15 +72,15 @@ process* dnsproxy_load(const char *caption, dnsproxy *info, const char *file) {
         log_fatal("%s without primary dns server", caption);
     }
 
-    create_folder(WORK_DIR);
-    char *config = dnsproxy_config(info); // string config (JSON format)
+    create_folder(WORK_DIR); // ensure work dir exist
+    char *config = dnsproxy_config(info); // string config with json format
     char *config_file = string_join(WORK_DIR, file);
     save_file(config_file, config); // load dnsproxy configure
     free(config_file);
     free(config);
 
     char *option = string_join("--config-path=", file);
-    process *proc = process_init(caption, DNSPROXY_BIN);
+    process *proc = process_init(caption, DNSPROXY_BIN); // generate dnsproxy command
     process_add_arg(proc, option);
     if (info->debug) {
         process_add_arg(proc, "--verbose"); // dnsproxy enable debug mode
diff --git a/src/applet/overture.c b/src/applet/overture.c
index db5061b..6c9debb 100644
--- a/src/applet/overture.c
+++ b/src/applet/overture.c
@@ -8,11 +8,21 @@
 void overture_dump(overture *info);
 char* overture_config(overture *info);
 
+void overture_free(overture *info) { // free overture options
+    free(info->ttl_file); // free(NULL) is valid
+    free(info->host_file);
+    free(info->foreign_ip_file);
+    free(info->domestic_ip_file);
+    free(info->foreign_domain_file);
+    free(info->domestic_domain_file);
+    free(info);
+}
+
 overture* overture_init() { // init overture options
     overture *info = (overture *)malloc(sizeof(overture));
     info->port = DIVERTER_PORT;
     info->debug = FALSE;
-    info->timeout = DIVERTER_TIMEOUT; // default timeout -> 6s
+    info->timeout = DIVERTER_TIMEOUT; // default timeout
     info->ttl_file = NULL;
     info->host_file = NULL;
     info->foreign_port = FOREIGN_PORT;
@@ -25,7 +35,7 @@ overture* overture_init() { // init overture options
     return info;
 }
 
-void overture_dump(overture *info) { // show overture info in debug log
+void overture_dump(overture *info) { // show overture options in debug log
     char *reject_type = uint32_list_dump(info->reject_type);
     log_debug("Overture port -> %u", info->port);
     log_debug("Overture debug -> %s", show_bool(info->debug));
@@ -42,23 +52,23 @@ void overture_dump(overture *info) { // show overture info in debug log
     free(reject_type);
 }
 
-process* overture_load(overture *info, const char *file) {
+process* overture_load(overture *info, const char *file) { // load overture options
     overture_dump(info);
     if (!check_port(info->port)) { // invalid server port
         log_fatal("Invalid port `%u`", info->port);
     }
-    if (info->timeout == 0) {
+    if (info->timeout == 0) { // invalid timeout value
         log_fatal("Timeout of overture with invalid value 0");
     }
 
-    create_folder(WORK_DIR);
+    create_folder(WORK_DIR); // ensure work dir exist
     char *config = overture_config(info); // string config (JSON format)
     char *config_file = string_join(WORK_DIR, file);
     save_file(config_file, config);
     free(config_file);
     free(config);
 
-    process *proc = process_init("Overture", OVERTURE_BIN);
+    process *proc = process_init("Overture", OVERTURE_BIN); // generate overture command
     process_add_arg(proc, "-c");
     process_add_arg(proc, file);
     if (info->debug) {
diff --git a/src/cleardns.c b/src/cleardns.c
index 3302a52..944e263 100644
--- a/src/cleardns.c
+++ b/src/cleardns.c
@@ -41,8 +41,8 @@ int main(int argc, char *argv[]) { // ClearDNS server
     log_info("ClearDNS server start (%s)", VERSION);
 
 
-//    load_config("test.json");
-//
+    load_config("test.json");
+
 //    dnsproxy_load("Domestic", loader.domestic, "domestic.json");
 //    dnsproxy_load("Foreign", loader.foreign, "foreign.json");
 
@@ -110,20 +110,20 @@ int main(int argc, char *argv[]) { // ClearDNS server
 //    log_info("cwd -> %s", p->cwd);
 
 
-    adguard *filter = adguard_init();
-
-    filter->debug = TRUE;
-    filter->dns_port = 54;
-    filter->web_port = 8080;
-    filter->upstream = "127.0.0.1:5454";
-
-    filter->username = "dnomd343";
-    filter->password = "password";
-
-    process *p = adguard_load(filter, "/cleardns/adguard/");
-    log_info("cmd -> %s", string_list_dump(p->cmd));
-    log_info("env -> %s", string_list_dump(p->env));
-    log_info("cwd -> %s", p->cwd);
+//    adguard *filter = adguard_init();
+//
+//    filter->debug = TRUE;
+//    filter->dns_port = 54;
+//    filter->web_port = 8080;
+//    filter->upstream = "127.0.0.1:5454";
+//
+//    filter->username = "dnomd343";
+//    filter->password = "password";
+//
+//    process *p = adguard_load(filter, "/cleardns/adguard/");
+//    log_info("cmd -> %s", string_list_dump(p->cmd));
+//    log_info("env -> %s", string_list_dump(p->env));
+//    log_info("cwd -> %s", p->cwd);
 
 
 //    int debug_mode = 0;
diff --git a/src/loader/CMakeLists.txt b/src/loader/CMakeLists.txt
index 0acf9e5..dd1ef74 100644
--- a/src/loader/CMakeLists.txt
+++ b/src/loader/CMakeLists.txt
@@ -1,3 +1,4 @@
 cmake_minimum_required(VERSION 2.8.12)
 
 add_library(loader config.c loader.c parser.c)
+target_link_libraries(loader applet)
diff --git a/src/loader/config.c b/src/loader/config.c
index d47c2b6..8be2c2f 100644
--- a/src/loader/config.c
+++ b/src/loader/config.c
@@ -1,13 +1,13 @@
 #include <stdlib.h>
-#include "common.h"
 #include "config.h"
+#include "common.h"
 #include "logger.h"
 #include "structure.h"
 
 cleardns_config* config_init() { // init config struct of cleardns
     cleardns_config *config = (cleardns_config *)malloc(sizeof(cleardns_config));
     config->port = DNS_PORT;
-    config->cache.size = 0;
+    config->cache.size = 0; // disable cache in default
     config->cache.enable = FALSE;
     config->cache.optimistic = FALSE;
 
diff --git a/src/loader/loader.c b/src/loader/loader.c
index 0019858..a6c7f28 100644
--- a/src/loader/loader.c
+++ b/src/loader/loader.c
@@ -1,4 +1,3 @@
-#include <stdlib.h>
 #include "loader.h"
 #include "config.h"
 #include "parser.h"
@@ -34,9 +33,8 @@ dnsproxy* load_foreign(cleardns_config *config) {
 }
 
 overture* load_diverter(cleardns_config *config) {
-    overture *diverter = overture_init(config->diverter.port);
+    overture *diverter = overture_init();
 
-    // timeout
     // ttl_file
     // host_file
     // foreign_port
@@ -48,9 +46,26 @@ overture* load_diverter(cleardns_config *config) {
     // domestic_ip_file
     // foreign_domain_file
     // domestic_domain_file
+
+    // TODO: load assets file
+
     return diverter;
 }
 
+adguard* load_filter(cleardns_config *config) {
+    adguard *filter = adguard_init();
+
+    // dns_port
+    // web_port
+
+    // upstream
+
+    // username
+    // password
+
+    return filter;
+}
+
 void load_config(const char *config_file) {
     cleardns_config *config = config_init();
     config_parser(config, config_file);
@@ -61,6 +76,6 @@ void load_config(const char *config_file) {
     loader.domestic = load_domestic(config);
     loader.foreign = load_foreign(config);
     loader.diverter = load_diverter(config);
-    // load adguard
+    loader.filter = load_filter(config);
     config_free(config);
 }
diff --git a/src/loader/parser.c b/src/loader/parser.c
index af7442e..9cce1ec 100644
--- a/src/loader/parser.c
+++ b/src/loader/parser.c
@@ -4,75 +4,8 @@
 #include "common.h"
 #include "logger.h"
 #include "config.h"
-#include "structure.h"
 
-int json_int_value(char *key, cJSON *json) { // json int or string value -> int
-    if (cJSON_IsNumber(json)) {
-        return json->valueint;
-    } else if (cJSON_IsString(json)) {
-        char *p;
-        int int_ret = (int)strtol(json->valuestring, &p, 10);
-        if (int_ret == 0 && strcmp(json->valuestring, "0") != 0) { // invalid number in string
-            log_fatal("`%s` not a valid number", key);
-        }
-        return int_ret;
-    } else {
-        log_fatal("`%s` must be number or string", key);
-    }
-    return 0; // never reach
-}
-
-char* json_string_value(char* key, cJSON *json) {
-    if (!cJSON_IsString(json)) {
-        log_fatal("`%s` must be string", key);
-    }
-    return json->valuestring;
-}
-
-char** json_string_list_value(char *key, cJSON *json, char **string_list) {
-    if (cJSON_IsString(json)) {
-        string_list = string_list_append(string_list, json->valuestring);
-    } else if (cJSON_IsArray(json)) {
-        json = json->child;
-        while (json != NULL) {
-            if (!cJSON_IsString(json)) {
-                log_fatal("`%s` must be string array", key);
-            }
-            string_list = string_list_append(string_list, json->valuestring);
-            json = json->next; // next field
-        }
-    } else if (!cJSON_IsNull(json)) {
-        log_fatal("`%s` must be array or string", key);
-    }
-    return string_list;
-}
-
-uint32_t** json_uint32_list_value(char *key, cJSON *json, uint32_t **uint32_list) {
-    if (cJSON_IsNumber(json)) {
-        uint32_list = uint32_list_append(uint32_list, json->valueint);
-    } else if (cJSON_IsArray(json)) {
-        json = json->child;
-        while (json != NULL) {
-            if (!cJSON_IsNumber(json)) {
-                log_fatal("`%s` must be number array", key);
-            }
-            uint32_list = uint32_list_append(uint32_list, json->valueint);
-            json = json->next; // next field
-        }
-    } else if (!cJSON_IsNull(json)) {
-        log_fatal("`%s` must be array or number", key);
-    }
-    return uint32_list;
-}
-
-uint8_t json_bool_value(char *key, cJSON *json) { // json bool value -> bool
-    if (!cJSON_IsBool(json)) {
-        log_fatal("`%s` must be boolean", key);
-    }
-    return json->valueint;
-}
-
-void json_cache_parser(cache_config *config, cJSON *json) { // cache options parser
+void cache_parser(cache_config *config, cJSON *json) { // cache options parser
     if (!cJSON_IsObject(json)) {
         log_fatal("`cache` must be object");
     }
@@ -91,7 +24,7 @@ void json_cache_parser(cache_config *config, cJSON *json) { // cache options par
     }
 }
 
-void json_upstream_parser(char *caption, upstream_config *config, cJSON *json) {
+void upstream_parser(char *caption, upstream_config *config, cJSON *json) { // upstream options parser
     if (!cJSON_IsObject(json)) {
         log_fatal("`%s` must be object", caption);
     }
@@ -132,7 +65,7 @@ void json_upstream_parser(char *caption, upstream_config *config, cJSON *json) {
     }
 }
 
-void json_diverter_parser(diverter_config *config, cJSON *json) { // diverter options parser
+void diverter_parser(diverter_config *config, cJSON *json) { // diverter options parser
     if (!cJSON_IsObject(json)) {
         log_fatal("`diverter` must be object");
     }
@@ -154,7 +87,7 @@ void json_diverter_parser(diverter_config *config, cJSON *json) { // diverter op
     }
 }
 
-void json_adguard_parser(adguard_config *config, cJSON *json) { // adguard options parser
+void adguard_parser(adguard_config *config, cJSON *json) { // adguard options parser
     if (!cJSON_IsObject(json)) {
         log_fatal("`adguard` must be array");
     }
@@ -167,19 +100,21 @@ void json_adguard_parser(adguard_config *config, cJSON *json) { // adguard optio
             config->enable = json_bool_value("adguard.enable", json);
         }
         if (!strcmp(json->string, "username")) {
+            free(config->username);
             config->username = json_string_value("adguard.username", json);
         }
         if (!strcmp(json->string, "password")) {
+            free(config->password);
             config->password = json_string_value("adguard.password", json);
         }
         json = json->next; // next field
     }
 }
 
-void json_config_parser(cleardns_config *config, const char *config_content) { // JSON format configure
+void cleardns_parser(cleardns_config *config, const char *config_content) { // JSON format configure
     cJSON *json = cJSON_Parse(config_content);
     if (json == NULL) {
-        log_fatal("JSON configure format error");
+        log_fatal("ClearDNS configure format error");
     }
     json = json->child;
     while (json != NULL) {
@@ -187,19 +122,19 @@ void json_config_parser(cleardns_config *config, const char *config_content) { /
             config->port = json_int_value("port", json);
         }
         if (!strcmp(json->string, "cache")) {
-            json_cache_parser(&config->cache, json);
+            cache_parser(&config->cache, json);
         }
         if (!strcmp(json->string, "domestic")) {
-            json_upstream_parser("domestic", &config->domestic, json);
+            upstream_parser("domestic", &config->domestic, json);
         }
         if (!strcmp(json->string, "foreign")) {
-            json_upstream_parser("foreign", &config->foreign, json);
+            upstream_parser("foreign", &config->foreign, json);
         }
         if (!strcmp(json->string, "diverter")) {
-            json_diverter_parser(&config->diverter, json);
+            diverter_parser(&config->diverter, json);
         }
         if (!strcmp(json->string, "adguard")) {
-            json_adguard_parser(&config->adguard, json);
+            adguard_parser(&config->adguard, json);
         }
         if (!strcmp(json->string, "reject")) {
             config->reject = json_uint32_list_value("reject", json, config->reject);
@@ -215,31 +150,20 @@ void json_config_parser(cleardns_config *config, const char *config_content) { /
     cJSON_free(json); // free JSON struct
 }
 
-void yaml_config_parser(cleardns_config *config, const char *config_content) { // YAML format configure
-    // TODO: change YAML -> JSON
-    char *json_content = string_init(config_content); // just demo for now
-
-    json_config_parser(config, json_content);
-}
-
-uint8_t is_json_suffix(const char *file_name) {
-    if (strlen(file_name) <= 5) { // `.json`
-        return FALSE;
-    }
-    if (!strcmp(file_name + strlen(file_name) - 5, ".json")) {
-        return TRUE;
-    }
-    return FALSE;
-}
-
 void config_parser(cleardns_config *config, const char *config_file) {
     char *config_content = read_file(config_file);
-    if (is_json_suffix(config_file)) {
+    if (is_json_suffix(config_file)) { // JSON format
         log_info("Start JSON configure parser");
-        json_config_parser(config, config_content);
-    } else {
-        log_info("Start YAML configure parser");
-        yaml_config_parser(config, config_content);
+        cleardns_parser(config, config_content); // configure parser
+    } else { // YAML or TOML format
+        log_info("Start configure parser");
+        char *json_content = to_json(config_content); // convert to json format
+        if (json_content == NULL) {
+            log_fatal("Configure parser error");
+        }
+        cleardns_parser(config, json_content); // configure parser
+        free(json_content);
     }
+    free(config_content);
     log_info("Configure parser success");
 }
diff --git a/src/utils/json.c b/src/utils/json.c
index e6ae4a2..4250e66 100644
--- a/src/utils/json.c
+++ b/src/utils/json.c
@@ -4,6 +4,7 @@
 #include "cJSON.h"
 #include "logger.h"
 #include "common.h"
+#include "structure.h"
 
 char* to_json(const char *file) {
     char flag[9];
@@ -36,6 +37,72 @@ void json_field_replace(cJSON *entry, const char *field, cJSON *content) {
     }
 }
 
+int json_int_value(char *key, cJSON *json) { // json int or string value -> int
+    if (cJSON_IsNumber(json)) {
+        return json->valueint;
+    } else if (cJSON_IsString(json)) {
+        char *p;
+        int int_ret = (int)strtol(json->valuestring, &p, 10);
+        if (int_ret == 0 && strcmp(json->valuestring, "0") != 0) { // invalid number in string
+            log_fatal("`%s` not a valid number", key);
+        }
+        return int_ret;
+    } else {
+        log_fatal("`%s` must be number or string", key);
+    }
+    return 0; // never reach
+}
+
+char* json_string_value(char* key, cJSON *json) {
+    if (!cJSON_IsString(json)) {
+        log_fatal("`%s` must be string", key);
+    }
+    return string_init(json->valuestring);
+}
+
+char** json_string_list_value(char *key, cJSON *json, char **string_list) {
+    if (cJSON_IsString(json)) {
+        string_list = string_list_append(string_list, json->valuestring);
+    } else if (cJSON_IsArray(json)) {
+        json = json->child;
+        while (json != NULL) {
+            if (!cJSON_IsString(json)) {
+                log_fatal("`%s` must be string array", key);
+            }
+            string_list = string_list_append(string_list, json->valuestring);
+            json = json->next; // next field
+        }
+    } else if (!cJSON_IsNull(json)) {
+        log_fatal("`%s` must be array or string", key);
+    }
+    return string_list;
+}
+
+uint32_t** json_uint32_list_value(char *key, cJSON *json, uint32_t **uint32_list) {
+    if (cJSON_IsNumber(json)) {
+        uint32_list = uint32_list_append(uint32_list, json->valueint);
+    } else if (cJSON_IsArray(json)) {
+        json = json->child;
+        while (json != NULL) {
+            if (!cJSON_IsNumber(json)) {
+                log_fatal("`%s` must be number array", key);
+            }
+            uint32_list = uint32_list_append(uint32_list, json->valueint);
+            json = json->next; // next field
+        }
+    } else if (!cJSON_IsNull(json)) {
+        log_fatal("`%s` must be array or number", key);
+    }
+    return uint32_list;
+}
+
+uint8_t json_bool_value(char *key, cJSON *json) { // json bool value -> bool
+    if (!cJSON_IsBool(json)) {
+        log_fatal("`%s` must be boolean", key);
+    }
+    return json->valueint;
+}
+
 cJSON* json_field_get(cJSON *entry, const char *field) {
     cJSON *sub = entry->child;
     while (sub != NULL) {
@@ -48,3 +115,13 @@ cJSON* json_field_get(cJSON *entry, const char *field) {
     cJSON_AddItemToObject(entry, field, new);
     return new;
 }
+
+uint8_t is_json_suffix(const char *file_name) {
+    if (strlen(file_name) <= 5) { // `.json`
+        return FALSE;
+    }
+    if (!strcmp(file_name + strlen(file_name) - 5, ".json")) {
+        return TRUE;
+    }
+    return FALSE;
+}
diff --git a/src/utils/structure.c b/src/utils/structure.c
index 95f081d..87f549d 100644
--- a/src/utils/structure.c
+++ b/src/utils/structure.c
@@ -1,5 +1,4 @@
 #include <stdio.h>
-
 #include <string.h>
 #include <stdlib.h>
 #include "structure.h"