diff --git a/src/api/config.c b/src/api/config.c
index a9b9eafd..c2c7a71e 100644
--- a/src/api/config.c
+++ b/src/api/config.c
@@ -768,7 +768,7 @@ static int api_config_patch(struct ftl_conn *api)
 
 		// Validate new value (if validation function is defined)
 		char errbuf[VALIDATOR_ERRBUF_LEN] = { 0 };
-		if(!conf_item->c(&new_item->v, errbuf))
+		if(!conf_item->c(&new_item->v, new_item->k, errbuf))
 		{
 			free_config(&newconf);
 			return send_json_error(api, 400,
@@ -965,7 +965,7 @@ static int api_config_put_delete(struct ftl_conn *api)
 		if(api->method == HTTP_PUT)
 		{
 			char errbuf[VALIDATOR_ERRBUF_LEN] = { 0 };
-			if(!new_item->c(&new_item->v, errbuf))
+			if(!new_item->c(&new_item->v, new_item->k, errbuf))
 			{
 				free_config(&newconf);
 				return send_json_error(api, 400,
diff --git a/src/config/cli.c b/src/config/cli.c
index 0385d8d6..37289641 100644
--- a/src/config/cli.c
+++ b/src/config/cli.c
@@ -442,7 +442,7 @@ int set_config_from_CLI(const char *key, const char *value)
 		if(new_item->c != NULL)
 		{
 			char errbuf[VALIDATOR_ERRBUF_LEN] = { 0 };
-			if(!new_item->c(&new_item->v, errbuf))
+			if(!new_item->c(&new_item->v, new_item->k, errbuf))
 			{
 				free_config(&newconf);
 				log_err("Invalid value: %s", errbuf);
diff --git a/src/config/config.h b/src/config/config.h
index 180bc907..3f4a0e19 100644
--- a/src/config/config.h
+++ b/src/config/config.h
@@ -111,7 +111,7 @@ struct conf_item {
 	uint8_t f;            // additional Flags
 	union conf_value v;   // current Value
 	union conf_value d;   // Default value
-	bool (*c)(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN]); // Function pointer to validate the value
+	bool (*c)(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN]); // Function pointer to validate the value
 };
 
 struct enum_options {
diff --git a/src/config/validator.c b/src/config/validator.c
index 9c921510..5b6a929b 100644
--- a/src/config/validator.c
+++ b/src/config/validator.c
@@ -17,31 +17,31 @@
 
 // Stub validator for config types that need to dedicated validation as they can
 // be tested by their type only (e.g., integers, strings, booleans, enums, etc.)
-bool __attribute__((const)) validate_stub(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
+bool __attribute__((const)) validate_stub(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN])
 {
 	return true;
 }
 
 // Validate the dns.hosts array
 // Each entry needs to be a string in form "IP HOSTNAME"
-bool validate_dns_hosts(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
+bool validate_dns_hosts(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN])
 {
 	if(!cJSON_IsArray(val->json))
 	{
-		strncat(err, "Not an array", VALIDATOR_ERRBUF_LEN);
+		snprintf(err, VALIDATOR_ERRBUF_LEN, "%s: not an array", key);
 		return false;
 	}
 
-	for(int i = 1; i <= cJSON_GetArraySize(val->json); i++)
+	for(int i = 0; i < cJSON_GetArraySize(val->json); i++)
 	{
 		// Get array item
-		cJSON *item = cJSON_GetArrayItem(val->json, i-1);
+		cJSON *item = cJSON_GetArrayItem(val->json, i);
 
 		// Check if it's a string
 		if(!cJSON_IsString(item))
 		{
-			snprintf(err, VALIDATOR_ERRBUF_LEN, "%d%s element is not a string",
-			         i, get_ordinal_suffix(i));
+			snprintf(err, VALIDATOR_ERRBUF_LEN, "%s[%d]: not a string",
+			         key, i);
 			return false;
 		}
 
@@ -52,8 +52,8 @@ bool validate_dns_hosts(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 
 		if(!ip || !*ip)
 		{
-			snprintf(err, VALIDATOR_ERRBUF_LEN, "%d%s element does not have an IP address (\"%s\")",
-			         i, get_ordinal_suffix(i), item->valuestring);
+			snprintf(err, VALIDATOR_ERRBUF_LEN, "%s[%d]: not an IP address (\"%s\")",
+			         key, i, item->valuestring);
 			free(str);
 			return false;
 		}
@@ -63,8 +63,8 @@ bool validate_dns_hosts(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 		struct in6_addr addr6;
 		if(inet_pton(AF_INET, ip, &addr) != 1 && inet_pton(AF_INET6, ip, &addr6) != 1)
 		{
-			snprintf(err, VALIDATOR_ERRBUF_LEN, "%d%s element is neither a valid IPv4 nor IPv6 address (\"%s\")",
-			         i, get_ordinal_suffix(i), ip);
+			snprintf(err, VALIDATOR_ERRBUF_LEN, "%s[%d]: neither a valid IPv4 nor IPv6 address (\"%s\")",
+			         key, i, ip);
 			free(str);
 			return false;
 		}
@@ -78,8 +78,8 @@ bool validate_dns_hosts(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 		{
 			if(!valid_domain(host, strlen(host), false))
 			{
-				snprintf(err, VALIDATOR_ERRBUF_LEN, "%d%s element has an invalid hostname (\"%s\")",
-				         i, get_ordinal_suffix(i), host);
+				snprintf(err, VALIDATOR_ERRBUF_LEN, "%s[%d]: invalid hostname (\"%s\")",
+				         key, i, host);
 				free(str);
 				return false;
 			}
@@ -89,8 +89,8 @@ bool validate_dns_hosts(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 		// Check if there is at least one hostname in this record
 		if(hosts < 1)
 		{
-			snprintf(err, VALIDATOR_ERRBUF_LEN, "%d%s element does not have at least one hostname (\"%s\")",
-			         i, get_ordinal_suffix(i), item->valuestring);
+			snprintf(err, VALIDATOR_ERRBUF_LEN, "%s[%d]: entry does not have at least one hostname (\"%s\")",
+			         key, i, item->valuestring);
 			free(str);
 			return false;
 		}
@@ -103,23 +103,23 @@ bool validate_dns_hosts(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 
 // Validate the dns.cnames array
 // Each entry needs to be a string in form "<cname>,[<cname>,]<target>[,<TTL>]"
-bool validate_dns_cnames(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
+bool validate_dns_cnames(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN])
 {
 	if(!cJSON_IsArray(val->json))
 	{
-		strncat(err, "Not an array", VALIDATOR_ERRBUF_LEN);
+		snprintf(err, VALIDATOR_ERRBUF_LEN, "%s: not an array", key);
 		return false;
 	}
 
-	for(int i = 1; i <= cJSON_GetArraySize(val->json); i++)
+	for(int i = 0; i < cJSON_GetArraySize(val->json); i++)
 	{
 		// Get array item
-		cJSON *item = cJSON_GetArrayItem(val->json, i-1);
+		cJSON *item = cJSON_GetArrayItem(val->json, i);
 
 		// Check if it's a string
 		if(!cJSON_IsString(item))
 		{
-			snprintf(err, VALIDATOR_ERRBUF_LEN, "%d%s element is not a string", i, get_ordinal_suffix(i));
+			snprintf(err, VALIDATOR_ERRBUF_LEN, "%s[%d]: not a string", key, i);
 			return false;
 		}
 
@@ -141,7 +141,7 @@ bool validate_dns_cnames(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 			if(strlen(s) == 0)
 			{
 				// Contains an empty string
-				snprintf(err, VALIDATOR_ERRBUF_LEN, "%d%s element contains an empty string at position %u", i, get_ordinal_suffix(i), j);
+				snprintf(err, VALIDATOR_ERRBUF_LEN, "%s[%d]: contains an empty string at position %u", key, i, j);
 				free(str);
 				return false;
 			}
@@ -153,7 +153,7 @@ bool validate_dns_cnames(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 		// Check if there are at least one cname and a target
 		if(j < 2)
 		{
-			snprintf(err, VALIDATOR_ERRBUF_LEN, "%d%s element is not a valid CNAME definition", i, get_ordinal_suffix(i));
+			snprintf(err, VALIDATOR_ERRBUF_LEN, "%s[%d] element is not a valid CNAME definition", key, i);
 			return false;
 		}
 	}
@@ -162,7 +162,7 @@ bool validate_dns_cnames(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 }
 
 // Validate IPs in CIDR notation
-bool validate_cidr(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
+bool validate_cidr(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN])
 {
 	// Check if it's a valid CIDR
 	char *str = strdup(val->s);
@@ -174,7 +174,7 @@ bool validate_cidr(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 	// Check if there is an IP and no tail
 	if(!ip || !*ip || tail)
 	{
-		snprintf(err, VALIDATOR_ERRBUF_LEN, "Not a valid IP in CIDR notation (\"%s\")", val->s);
+		snprintf(err, VALIDATOR_ERRBUF_LEN, "%s: not a valid IP in CIDR notation (\"%s\")", key, val->s);
 		free(str);
 		return false;
 	}
@@ -185,7 +185,7 @@ bool validate_cidr(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 	int ip4 = 0, ip6 = 0;
 	if((ip4 = inet_pton(AF_INET, ip, &addr) != 1) && (ip6 = inet_pton(AF_INET6, ip, &addr6)) != 1)
 	{
-		snprintf(err, VALIDATOR_ERRBUF_LEN, "Not a valid IPv4 nor IPv6 address (\"%s\")", ip);
+		snprintf(err, VALIDATOR_ERRBUF_LEN, "%s: not a valid IPv4 nor IPv6 address (\"%s\")", key, ip);
 		free(str);
 		return false;
 	}
@@ -195,20 +195,20 @@ bool validate_cidr(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 	{
 		if(strlen(cidr) == 0)
 		{
-			strncat(err, "Empty CIDR value", VALIDATOR_ERRBUF_LEN);
+			snprintf(err, VALIDATOR_ERRBUF_LEN, "%s: empty CIDR value", key);
 			free(str);
 			return false;
 		}
 		int cidr_int = atoi(cidr);
 		if(ip4 && (cidr_int < 0 || cidr_int > 32))
 		{
-			snprintf(err, VALIDATOR_ERRBUF_LEN, "Not a valid IPv4 CIDR (\"%s\")", cidr);
+			snprintf(err, VALIDATOR_ERRBUF_LEN, "%s: not a valid IPv4 CIDR (\"%s\")", key, cidr);
 			free(str);
 			return false;
 		}
 		else if(ip6 && (cidr_int < 0 || cidr_int > 128))
 		{
-			snprintf(err, VALIDATOR_ERRBUF_LEN, "Not a valid IPv6 CIDR (\"%s\")", cidr);
+			snprintf(err, VALIDATOR_ERRBUF_LEN, "%s: not a valid IPv6 CIDR (\"%s\")", key, cidr);
 			free(str);
 			return false;
 		}
@@ -219,7 +219,7 @@ bool validate_cidr(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 }
 
 // Validate IP address optionally followed by a port (separator is "#")
-bool validate_ip_port(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
+bool validate_ip_port(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN])
 {
 	// Check if it's a valid IP
 	char *str = strdup(val->s);
@@ -231,7 +231,7 @@ bool validate_ip_port(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 	// Check if there is an IP and no tail
 	if(!ip || !*ip || tail)
 	{
-		snprintf(err, VALIDATOR_ERRBUF_LEN, "Not a valid IP (\"%s\")", val->s);
+		snprintf(err, VALIDATOR_ERRBUF_LEN, "%s: not a valid IP (\"%s\")", key, val->s);
 		free(str);
 		return false;
 	}
@@ -242,7 +242,7 @@ bool validate_ip_port(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 	int ip4 = 0, ip6 = 0;
 	if((ip4 = inet_pton(AF_INET, ip, &addr) != 1) && (ip6 = inet_pton(AF_INET6, ip, &addr6)) != 1)
 	{
-		snprintf(err, VALIDATOR_ERRBUF_LEN, "Not a valid IPv4 nor IPv6 address (\"%s\")", ip);
+		snprintf(err, VALIDATOR_ERRBUF_LEN, "%s: not a valid IPv4 nor IPv6 address (\"%s\")", key, ip);
 		free(str);
 		return false;
 	}
@@ -252,14 +252,14 @@ bool validate_ip_port(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 	{
 		if(strlen(port) == 0)
 		{
-			strncat(err, "Empty port value", VALIDATOR_ERRBUF_LEN);
+			snprintf(err, VALIDATOR_ERRBUF_LEN, "%s: empty port value", key);
 			free(str);
 			return false;
 		}
 		int port_int = atoi(port);
 		if(port_int < 0 || port_int > 65535)
 		{
-			snprintf(err, VALIDATOR_ERRBUF_LEN, "Not a valid port (\"%s\")", port);
+			snprintf(err, VALIDATOR_ERRBUF_LEN, "%s: not a valid port (\"%s\")", key, port);
 			free(str);
 			return false;
 		}
@@ -270,12 +270,12 @@ bool validate_ip_port(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 }
 
 // Validate domain
-bool validate_domain(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
+bool validate_domain(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN])
 {
 	// Check if domain is valid
 	if(!valid_domain(val->s, strlen(val->s), false))
 	{
-		snprintf(err, VALIDATOR_ERRBUF_LEN, "Not a valid domain (\"%s\")", val->s);
+		snprintf(err, VALIDATOR_ERRBUF_LEN, "%s: not a valid domain (\"%s\")", key, val->s);
 		return false;
 	}
 
@@ -283,14 +283,14 @@ bool validate_domain(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 }
 
 // Validate file path
-bool validate_filepath(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
+bool validate_filepath(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN])
 {
 	// Check if the path contains only valid characters
 	for(unsigned int i = 0; i < strlen(val->s); i++)
 	{
 		if(!isalnum(val->s[i]) && val->s[i] != '/' && val->s[i] != '.' && val->s[i] != '-' && val->s[i] != '_' && val->s[i] != ' ')
 		{
-			snprintf(err, VALIDATOR_ERRBUF_LEN, "Not a valid file path (\"%s\")", val->s);
+			snprintf(err, VALIDATOR_ERRBUF_LEN, "%s: not a valid file path (\"%s\")", key, val->s);
 			return false;
 		}
 	}
@@ -299,14 +299,14 @@ bool validate_filepath(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 }
 
 // Validate file path (empty allowed)
-bool validate_filepath_empty(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
+bool validate_filepath_empty(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN])
 {
 	// Empty paths are allowed, e.g., to disable a feature like PCAP
 	if(strlen(val->s) == 0)
 		return true;
 
 	// else:
-	return validate_filepath(val, err);
+	return validate_filepath(val, key, err);
 }
 
 // Validate a single regular expression
@@ -329,24 +329,24 @@ static bool validate_regex(const char *regex, char err[VALIDATOR_ERRBUF_LEN])
 }
 
 // Validate array of regexes
-bool validate_regex_array(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
+bool validate_regex_array(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN])
 {
 	if(val == NULL || !cJSON_IsArray(val->json))
 	{
-		strncat(err, "Not an array", VALIDATOR_ERRBUF_LEN);
+		strncat(err, "%s: not an array", VALIDATOR_ERRBUF_LEN);
 		return false;
 	}
 
-	for(int i = 1; i <= cJSON_GetArraySize(val->json); i++)
+	for(int i = 0; i < cJSON_GetArraySize(val->json); i++)
 	{
 		// Get array item
-		cJSON *item = cJSON_GetArrayItem(val->json, i-1);
+		cJSON *item = cJSON_GetArrayItem(val->json, i);
 
 		// Check if it's a string
 		if(!cJSON_IsString(item))
 		{
-			snprintf(err, VALIDATOR_ERRBUF_LEN, "%d%s element is not a string",
-			         i, get_ordinal_suffix(i));
+			snprintf(err, VALIDATOR_ERRBUF_LEN, "%s[%d]: not a string",
+			         key, i);
 			return false;
 		}
 
@@ -354,8 +354,8 @@ bool validate_regex_array(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN])
 		char errbuf[VALIDATOR_ERRBUF_LEN] = { 0 };
 		if(!validate_regex(item->valuestring, errbuf))
 		{
-			snprintf(err, VALIDATOR_ERRBUF_LEN, "%d%s element is not a valid regex (\"%s\"): %s",
-			         i, get_ordinal_suffix(i), item->valuestring, errbuf);
+			snprintf(err, VALIDATOR_ERRBUF_LEN, "%s[%d]: not a valid regex (\"%s\"): %s",
+			         key, i, item->valuestring, errbuf);
 			return false;
 		}
 	}
diff --git a/src/config/validator.h b/src/config/validator.h
index dbe4e7bd..27249f5f 100644
--- a/src/config/validator.h
+++ b/src/config/validator.h
@@ -14,14 +14,14 @@
 #include "FTL.h"
 #include "config/config.h"
 
-bool validate_stub(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN]) __attribute__((const));
-bool validate_dns_hosts(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN]);
-bool validate_dns_cnames(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN]);
-bool validate_cidr(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN]);
-bool validate_ip_port(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN]);
-bool validate_domain(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN]);
-bool validate_filepath(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN]);
-bool validate_filepath_empty(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN]);
-bool validate_regex_array(union conf_value *val, char err[VALIDATOR_ERRBUF_LEN]);
+bool validate_stub(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN]) __attribute__((const));
+bool validate_dns_hosts(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN]);
+bool validate_dns_cnames(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN]);
+bool validate_cidr(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN]);
+bool validate_ip_port(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN]);
+bool validate_domain(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN]);
+bool validate_filepath(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN]);
+bool validate_filepath_empty(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN]);
+bool validate_regex_array(union conf_value *val, const char *key, char err[VALIDATOR_ERRBUF_LEN]);
 
 #endif // CONFIG_VALIDATOR_H