diff --git a/include/h.h b/include/h.h
index b3fb7c798..78b94e417 100644
--- a/include/h.h
+++ b/include/h.h
@@ -670,7 +670,7 @@ extern void del_async_connects(void);
 extern void isupport_init(void);
 extern void clicap_init(void);
 extern void efunctions_init(void);
-extern void do_cmd(Client *client, MessageTag *mtags, char *cmd, int parc, char *parv[]);
+extern void do_cmd(Client *client, MessageTag *mtags, const char *cmd, int parc, char *parv[]);
 extern MODVAR char *me_hash;
 extern MODVAR int dontspread;
 extern MODVAR int labeled_response_inhibit;
@@ -755,7 +755,7 @@ extern MODVAR char *(*charsys_get_current_languages)(void);
 extern MODVAR void (*broadcast_sinfo)(Client *acptr, Client *to, Client *except);
 extern MODVAR void (*connect_server)(ConfigItem_link *aconf, Client *by, struct hostent *hp);
 extern MODVAR void (*parse_message_tags)(Client *cptr, char **str, MessageTag **mtag_list);
-extern MODVAR char *(*mtags_to_string)(MessageTag *m, Client *acptr);
+extern MODVAR const char *(*mtags_to_string)(MessageTag *m, Client *acptr);
 extern MODVAR int (*can_send_to_channel)(Client *cptr, Channel *channel, const char **msgtext, const char **errmsg, int notice);
 extern MODVAR void (*broadcast_md_globalvar)(ModDataInfo *mdi, ModData *md);
 extern MODVAR void (*broadcast_md_globalvar_cmd)(Client *except, Client *sender, const char *varname, const char *value);
@@ -803,7 +803,7 @@ extern MODVAR EVP_MD *md5_function;
 /* End of TLS functions */
 
 extern void parse_message_tags_default_handler(Client *client, char **str, MessageTag **mtag_list);
-extern char *mtags_to_string_default_handler(MessageTag *m, Client *client);
+extern const char *mtags_to_string_default_handler(MessageTag *m, Client *client);
 extern void *labeled_response_save_context_default_handler(void);
 extern void labeled_response_set_context_default_handler(void *ctx);
 extern void labeled_response_force_end_default_handler(void);
diff --git a/include/modules.h b/include/modules.h
index 965854797..783b28340 100644
--- a/include/modules.h
+++ b/include/modules.h
@@ -483,13 +483,13 @@ typedef struct {
 /** Message Tag Handler */
 struct MessageTagHandler {
 	MessageTagHandler *prev, *next;
-	char *name;                                 /**< The name of the message-tag */
-	int flags;                                  /**< A flag of MTAG_HANDLER_FLAGS_* */
-	int (*is_ok)(Client *, char *, char *);     /**< Verify syntax and access rights */
-	int (*should_send_to_client)(Client *);     /**< Tag may be sent to this client (normally NULL!) */
-	Module *owner;                              /**< Module introducing this CAP. */
-	ClientCapability *clicap_handler;           /**< Client capability handler associated with this */
-	char unloaded;                              /**< Internal flag to indicate module is being unloaded */
+	char *name;                                             /**< The name of the message-tag */
+	int flags;                                              /**< A flag of MTAG_HANDLER_FLAGS_* */
+	int (*is_ok)(Client *, const char *, const char *);     /**< Verify syntax and access rights */
+	int (*should_send_to_client)(Client *);                 /**< Tag may be sent to this client (normally NULL!) */
+	Module *owner;                                          /**< Module introducing this CAP. */
+	ClientCapability *clicap_handler;                       /**< Client capability handler associated with this */
+	char unloaded;                                          /**< Internal flag to indicate module is being unloaded */
 };
 
 /** The struct used to register a message tag handler.
@@ -498,7 +498,7 @@ struct MessageTagHandler {
 typedef struct {
 	char *name;
 	int flags;
-	int (*is_ok)(Client *, char *, char *);
+	int (*is_ok)(Client *, const char *, const char *);
 	int (*should_send_to_client)(Client *);
 	ClientCapability *clicap_handler;
 } MessageTagHandlerInfo;
@@ -549,10 +549,10 @@ typedef struct HistoryBackend HistoryBackend;
 struct HistoryBackend {
 	HistoryBackend *prev, *next;
 	char *name;                                   /**< The name of the history backend (eg: "mem") */
-	int (*history_set_limit)(char *object, int max_lines, long max_time); /**< Impose a limit on a history object */
-	int (*history_add)(char *object, MessageTag *mtags, char *line); /**< Add to history */
-	HistoryResult *(*history_request)(char *object, HistoryFilter *filter);  /**< Request history */
-	int (*history_destroy)(char *object);  /**< Destroy history of this object completely */
+	int (*history_set_limit)(const char *object, int max_lines, long max_time); /**< Impose a limit on a history object */
+	int (*history_add)(const char *object, MessageTag *mtags, const char *line); /**< Add to history */
+	HistoryResult *(*history_request)(const char *object, HistoryFilter *filter);  /**< Request history */
+	int (*history_destroy)(const char *object);  /**< Destroy history of this object completely */
 	Module *owner;                                /**< Module introducing this */
 	char unloaded;                                /**< Internal flag to indicate module is being unloaded */
 };
@@ -562,10 +562,10 @@ struct HistoryBackend {
  */
 typedef struct {
 	char *name;
-	int (*history_set_limit)(char *object, int max_lines, long max_time);
-	int (*history_add)(char *object, MessageTag *mtags, char *line);
-	HistoryResult *(*history_request)(char *object, HistoryFilter *filter);
-	int (*history_destroy)(char *object);
+	int (*history_set_limit)(const char *object, int max_lines, long max_time);
+	int (*history_add)(const char *object, MessageTag *mtags, const char *line);
+	HistoryResult *(*history_request)(const char *object, HistoryFilter *filter);
+	int (*history_destroy)(const char *object);
 } HistoryBackendInfo;
 
 struct Hook {
@@ -739,10 +739,10 @@ extern MODVAR Hooktype		Hooktypes[MAXCUSTOMHOOKS];
 extern MODVAR Callback *Callbacks[MAXCALLBACKS], *RCallbacks[MAXCALLBACKS];
 extern MODVAR ClientCapability *clicaps;
 
-extern Event *EventAdd(Module *module, char *name, vFP event, void *data, long every_msec, int count);
+extern Event *EventAdd(Module *module, const char *name, vFP event, void *data, long every_msec, int count);
 extern void   EventDel(Event *event);
 extern Event *EventMarkDel(Event *event);
-extern Event *EventFind(char *name);
+extern Event *EventFind(const char *name);
 extern int EventMod(Event *event, EventInfo *mods);
 extern void DoEvents(void);
 extern void EventStatus(Client *client);
@@ -823,7 +823,7 @@ __extension__ ({ \
 extern Hook	*HookAddMain(Module *module, int hooktype, int priority, int (*intfunc)(), void (*voidfunc)(), char *(*stringfunc)(), const char *(*conststringfunc)());
 extern Hook	*HookDel(Hook *hook);
 
-extern Hooktype *HooktypeAdd(Module *module, char *string, int *type);
+extern Hooktype *HooktypeAdd(Module *module, const char *string, int *type);
 extern void HooktypeDel(Hooktype *hooktype, Module *module);
 
 #define RunHook(hooktype,...) do { Hook *h; for (h = Hooks[hooktype]; h; h = h->next) (*(h->func.intfunc))(__VA_ARGS__); } while(0)
@@ -866,8 +866,8 @@ extern Callback	*CallbackDel(Callback *cb);
 extern Efunction *EfunctionAddMain(Module *module, EfunctionType eftype, int (*intfunc)(), void (*voidfunc)(), void *(*pvoidfunc)(), char *(*stringfunc)(), const char *(*conststringfunc)());
 extern Efunction *EfunctionDel(Efunction *cb);
 
-extern Command *CommandAdd(Module *module, char *cmd, CmdFunc func, unsigned char params, int flags);
-extern Command *AliasAdd(Module *module, char *cmd, AliasCmdFunc aliasfunc, unsigned char params, int flags);
+extern Command *CommandAdd(Module *module, const char *cmd, CmdFunc func, unsigned char params, int flags);
+extern Command *AliasAdd(Module *module, const char *cmd, AliasCmdFunc aliasfunc, unsigned char params, int flags);
 extern void CommandDel(Command *command);
 extern void CommandDelX(Command *command, RealCommand *cmd);
 extern int CommandExists(const char *name);
diff --git a/src/api-command.c b/src/api-command.c
index 3ce6501a8..a6054639f 100644
--- a/src/api-command.c
+++ b/src/api-command.c
@@ -23,8 +23,8 @@
 #include "unrealircd.h"
 
 /* Forward declarations */
-static Command *CommandAddInternal(Module *module, char *cmd, CmdFunc func, AliasCmdFunc aliasfunc, unsigned char params, int flags);
-static RealCommand *add_Command_backend(char *cmd);
+static Command *CommandAddInternal(Module *module, const char *cmd, CmdFunc func, AliasCmdFunc aliasfunc, unsigned char params, int flags);
+static RealCommand *add_Command_backend(const char *cmd);
 
 /** @defgroup CommandAPI Command API
  * @{
@@ -53,7 +53,7 @@ int CommandExists(const char *name)
  * @param flags		Who may execute this command - one or more CMD_* flags
  * @returns The newly registered command, or NULL in case of error (eg: already exist)
  */
-Command *CommandAdd(Module *module, char *cmd, CmdFunc func, unsigned char params, int flags)
+Command *CommandAdd(Module *module, const char *cmd, CmdFunc func, unsigned char params, int flags)
 {
 	if (flags & CMD_ALIAS)
 	{
@@ -75,7 +75,7 @@ Command *CommandAdd(Module *module, char *cmd, CmdFunc func, unsigned char param
  * @param flags		Who may execute this command - one or more CMD_* flags
  * @returns The newly registered command (alias), or NULL in case of error (eg: already exist)
  */
-Command *AliasAdd(Module *module, char *cmd, AliasCmdFunc aliasfunc, unsigned char params, int flags)
+Command *AliasAdd(Module *module, const char *cmd, AliasCmdFunc aliasfunc, unsigned char params, int flags)
 {
 	if (!(flags & CMD_ALIAS))
 		flags |= CMD_ALIAS;
@@ -84,7 +84,7 @@ Command *AliasAdd(Module *module, char *cmd, AliasCmdFunc aliasfunc, unsigned ch
 
 /** @} */
 
-static Command *CommandAddInternal(Module *module, char *cmd, CmdFunc func, AliasCmdFunc aliasfunc, unsigned char params, int flags)
+static Command *CommandAddInternal(Module *module, const char *cmd, CmdFunc func, AliasCmdFunc aliasfunc, unsigned char params, int flags)
 {
 	Command *command = NULL;
 	RealCommand *c;
@@ -191,7 +191,7 @@ void CommandDel(Command *command)
  * @note If mtags is NULL then new message tags are created for the command
  *       (and destroyed before return).
  */
-void do_cmd(Client *client, MessageTag *mtags, char *cmd, int parc, char *parv[])
+void do_cmd(Client *client, MessageTag *mtags, const char *cmd, int parc, char *parv[])
 {
 	RealCommand *cmptr;
 
@@ -233,7 +233,7 @@ void init_CommandHash(void)
 	CommandAdd(NULL, MSG_MODULE, cmd_module, MAXPARA, CMD_USER);
 }
 
-static RealCommand *add_Command_backend(char *cmd)
+static RealCommand *add_Command_backend(const char *cmd)
 {
 	RealCommand *c = safe_alloc(sizeof(RealCommand));
 
diff --git a/src/api-efunctions.c b/src/api-efunctions.c
index 678f16d6b..833a8d83f 100644
--- a/src/api-efunctions.c
+++ b/src/api-efunctions.c
@@ -105,7 +105,7 @@ char *(*charsys_get_current_languages)(void);
 void (*broadcast_sinfo)(Client *client, Client *to, Client *except);
 void (*connect_server)(ConfigItem_link *aconf, Client *by, struct hostent *hp);
 void (*parse_message_tags)(Client *client, char **str, MessageTag **mtag_list);
-char *(*mtags_to_string)(MessageTag *m, Client *client);
+const char *(*mtags_to_string)(MessageTag *m, Client *client);
 int (*can_send_to_channel)(Client *client, Channel *channel, const char **msgtext, const char **errmsg, int notice);
 void (*broadcast_md_globalvar)(ModDataInfo *mdi, ModData *md);
 void (*broadcast_md_globalvar_cmd)(Client *except, Client *sender, const char *varname, const char *value);
diff --git a/src/api-event.c b/src/api-event.c
index 98ee3a42d..9b2b5778e 100644
--- a/src/api-event.c
+++ b/src/api-event.c
@@ -45,7 +45,7 @@ extern EVENT(unrealdb_expire_secret_cache);
  *        can be later, in case of high load, in very extreme cases even up to 1000 or 2000
  *        msec later but that would be very unusual. Just saying, it's not a guarantee..
  */
-Event *EventAdd(Module *module, char *name, vFP event, void *data, long every_msec, int count)
+Event *EventAdd(Module *module, const char *name, vFP event, void *data, long every_msec, int count)
 {
 	Event *newevent;
 
@@ -147,7 +147,7 @@ static void CleanupEvents(void)
 	}
 }
 
-Event *EventFind(char *name)
+Event *EventFind(const char *name)
 {
 	Event *eventptr;
 
diff --git a/src/misc.c b/src/misc.c
index 25ed6b670..2722d67cf 100644
--- a/src/misc.c
+++ b/src/misc.c
@@ -1454,7 +1454,7 @@ void parse_message_tags_default_handler(Client *client, char **str, MessageTag *
  * This is only used if the 'mtags' module is NOT loaded,
  * which would be quite unusual, but possible.
  */
-char *mtags_to_string_default_handler(MessageTag *m, Client *client)
+const char *mtags_to_string_default_handler(MessageTag *m, Client *client)
 {
 	return NULL;
 }
diff --git a/src/modules/account-tag.c b/src/modules/account-tag.c
index 7c66ac5e2..b23578ae5 100644
--- a/src/modules/account-tag.c
+++ b/src/modules/account-tag.c
@@ -34,7 +34,7 @@ ModuleHeader MOD_HEADER
 /* Variables */
 long CAP_ACCOUNT_TAG = 0L;
 
-int account_tag_mtag_is_ok(Client *client, char *name, char *value);
+int account_tag_mtag_is_ok(Client *client, const char *name, const char *value);
 void mtag_add_account(Client *client, MessageTag *recv_mtags, MessageTag **mtag_list, const char *signature);
 
 MOD_INIT()
@@ -75,7 +75,7 @@ MOD_UNLOAD()
  * syntax.
  * We simply allow account-tag ONLY from servers and with any syntax.
  */
-int account_tag_mtag_is_ok(Client *client, char *name, char *value)
+int account_tag_mtag_is_ok(Client *client, const char *name, const char *value)
 {
 	if (IsServer(client))
 		return 1;
diff --git a/src/modules/batch.c b/src/modules/batch.c
index 4c8b6fda7..692680c4d 100644
--- a/src/modules/batch.c
+++ b/src/modules/batch.c
@@ -37,7 +37,7 @@ CMD_FUNC(cmd_batch);
 /* Variables */
 long CAP_BATCH = 0L;
 
-int batch_mtag_is_ok(Client *client, char *name, char *value);
+int batch_mtag_is_ok(Client *client, const char *name, const char *value);
 
 MOD_INIT()
 {
@@ -111,7 +111,7 @@ CMD_FUNC(cmd_batch)
  * syntax.
  * We simply allow batch ONLY from servers and with any syntax.
  */
-int batch_mtag_is_ok(Client *client, char *name, char *value)
+int batch_mtag_is_ok(Client *client, const char *name, const char *value)
 {
 	if (IsServer(client))
 		return 1;
diff --git a/src/modules/bot-tag.c b/src/modules/bot-tag.c
index c5c6bf7d7..2a300c360 100644
--- a/src/modules/bot-tag.c
+++ b/src/modules/bot-tag.c
@@ -36,7 +36,7 @@ ModuleHeader MOD_HEADER
 	"unrealircd-6",
 	};
 
-int bottag_mtag_is_ok(Client *client, char *name, char *value);
+int bottag_mtag_is_ok(Client *client, const char *name, const char *value);
 void mtag_add_bottag(Client *client, MessageTag *recv_mtags, MessageTag **mtag_list, const char *signature);
 
 MOD_INIT()
@@ -68,7 +68,7 @@ MOD_UNLOAD()
 
 /** This function verifies if the client sending the mtag is permitted to do so.
  */
-int bottag_mtag_is_ok(Client *client, char *name, char *value)
+int bottag_mtag_is_ok(Client *client, const char *name, const char *value)
 {
 	if (IsServer(client) && (value == NULL))
 		return 1; /* OK */
diff --git a/src/modules/history_backend_mem.c b/src/modules/history_backend_mem.c
index d443a18f1..03e3dbcab 100644
--- a/src/modules/history_backend_mem.c
+++ b/src/modules/history_backend_mem.c
@@ -97,16 +97,16 @@ static void freecfg(struct cfgstruct *cfg);
 static void hbm_init_hashes(ModuleInfo *m);
 static void init_history_storage(ModuleInfo *modinfo);
 int hbm_modechar_del(Channel *channel, int modechar);
-int hbm_history_add(char *object, MessageTag *mtags, char *line);
+int hbm_history_add(const char *object, MessageTag *mtags, const char *line);
 int hbm_history_cleanup(HistoryLogObject *h);
-HistoryResult *hbm_history_request(char *object, HistoryFilter *filter);
-int hbm_history_destroy(char *object);
-int hbm_history_set_limit(char *object, int max_lines, long max_time);
+HistoryResult *hbm_history_request(const char *object, HistoryFilter *filter);
+int hbm_history_destroy(const char *object);
+int hbm_history_set_limit(const char *object, int max_lines, long max_time);
 EVENT(history_mem_clean);
 EVENT(history_mem_init);
 static int hbm_read_masterdb(void);
 static void hbm_read_dbs(void);
-static int hbm_read_db(char *fname);
+static int hbm_read_db(const char *fname);
 static int hbm_write_masterdb(void);
 static int hbm_write_db(HistoryLogObject *h);
 static void hbm_delete_db(HistoryLogObject *h);
@@ -427,12 +427,12 @@ static void init_history_storage(ModuleInfo *modinfo)
 	ClientCapabilityAdd(modinfo->handle, &cap, NULL);
 }
 
-uint64_t hbm_hash(char *object)
+uint64_t hbm_hash(const char *object)
 {
 	return siphash_nocase(object, siphashkey_history_backend_mem) % HISTORY_BACKEND_MEM_HASH_TABLE_SIZE;
 }
 
-HistoryLogObject *hbm_find_object(char *object)
+HistoryLogObject *hbm_find_object(const char *object)
 {
 	int hashv = hbm_hash(object);
 	HistoryLogObject *h;
@@ -445,7 +445,7 @@ HistoryLogObject *hbm_find_object(char *object)
 	return NULL;
 }
 
-HistoryLogObject *hbm_find_or_add_object(char *object)
+HistoryLogObject *hbm_find_or_add_object(const char *object)
 {
 	int hashv = hbm_hash(object);
 	HistoryLogObject *h;
@@ -539,7 +539,7 @@ void hbm_duplicate_mtags(HistoryLogLine *l, MessageTag *m)
 }
 
 /** Add a line to a history object */
-void hbm_history_add_line(HistoryLogObject *h, MessageTag *mtags, char *line)
+void hbm_history_add_line(HistoryLogObject *h, MessageTag *mtags, const char *line)
 {
 	HistoryLogLine *l = safe_alloc(sizeof(HistoryLogLine) + strlen(line));
 	strcpy(l->line, line); /* safe, see memory allocation above ^ */
@@ -590,7 +590,7 @@ void hbm_history_del_line(HistoryLogObject *h, HistoryLogLine *l)
 }
 
 /** Add history entry */
-int hbm_history_add(char *object, MessageTag *mtags, char *line)
+int hbm_history_add(const char *object, MessageTag *mtags, const char *line)
 {
 	HistoryLogObject *h = hbm_find_or_add_object(object);
 	if (!h->max_lines)
@@ -958,7 +958,7 @@ static int hbm_return_between(HistoryResult *r, HistoryLogObject *h, HistoryFilt
 	return 0;
 }
 
-HistoryResult *hbm_history_request(char *object, HistoryFilter *filter)
+HistoryResult *hbm_history_request(const char *object, HistoryFilter *filter)
 {
 	HistoryResult *r;
 	HistoryLogObject *h = hbm_find_object(object);
@@ -1053,7 +1053,7 @@ int hbm_history_cleanup(HistoryLogObject *h)
 	return 1;
 }
 
-int hbm_history_destroy(char *object)
+int hbm_history_destroy(const char *object)
 {
 	HistoryLogObject *h = hbm_find_object(object);
 	HistoryLogLine *l, *l_next;
@@ -1078,7 +1078,7 @@ int hbm_history_destroy(char *object)
 }
 
 /** Set new limit on history object */
-int hbm_history_set_limit(char *object, int max_lines, long max_time)
+int hbm_history_set_limit(const char *object, int max_lines, long max_time)
 {
 	HistoryLogObject *h = hbm_find_or_add_object(object);
 	h->max_lines = max_lines;
@@ -1286,7 +1286,7 @@ static void hbm_read_dbs(void)
 
 
 /** Read a channel history db file */
-static int hbm_read_db(char *fname)
+static int hbm_read_db(const char *fname)
 {
 	UnrealDB *db = NULL;
 	// header
@@ -1486,7 +1486,7 @@ EVENT(history_mem_clean)
 	} while(loopcnt++ < HISTORY_CLEAN_PER_LOOP);
 }
 
-char *hbm_history_filename(HistoryLogObject *h)
+const char *hbm_history_filename(HistoryLogObject *h)
 {
 	static char fname[512];
 	char oname[OBJECTLEN+1];
@@ -1527,7 +1527,7 @@ char *hbm_history_filename(HistoryLogObject *h)
 static int hbm_write_db(HistoryLogObject *h)
 {
 	UnrealDB *db;
-	char *realfname;
+	const char *realfname;
 	char tmpfname[512];
 	HistoryLogLine *l;
 	MessageTag *m;
@@ -1600,7 +1600,7 @@ static int hbm_write_db(HistoryLogObject *h)
 static void hbm_delete_db(HistoryLogObject *h)
 {
 	UnrealDB *db;
-	char *fname;
+	const char *fname;
 	if (!cfg.persist || !hbm_prehash || !hbm_posthash)
 	{
 #ifdef DEBUGMODE
diff --git a/src/modules/history_backend_null.c b/src/modules/history_backend_null.c
index dca6e95fd..7136ce260 100644
--- a/src/modules/history_backend_null.c
+++ b/src/modules/history_backend_null.c
@@ -20,10 +20,10 @@ ModuleHeader MOD_HEADER
 };
 
 /* Forward declarations */
-int hbn_history_set_limit(char *object, int max_lines, long max_time);
-int hbn_history_add(char *object, MessageTag *mtags, char *line);
-HistoryResult *hbn_history_request(char *object, HistoryFilter *filter);
-int hbn_history_destroy(char *object);
+int hbn_history_set_limit(const char *object, int max_lines, long max_time);
+int hbn_history_add(const char *object, MessageTag *mtags, const char *line);
+HistoryResult *hbn_history_request(const char *object, HistoryFilter *filter);
+int hbn_history_destroy(const char *object);
 
 MOD_INIT()
 {
@@ -53,22 +53,22 @@ MOD_UNLOAD()
 	return MOD_SUCCESS;
 }
 
-int hbn_history_add(char *object, MessageTag *mtags, char *line)
+int hbn_history_add(const char *object, MessageTag *mtags, const char *line)
 {
 	return 1;
 }
 
-HistoryResult *hbn_history_request(char *object, HistoryFilter *filter)
+HistoryResult *hbn_history_request(const char *object, HistoryFilter *filter)
 {
 	return NULL;
 }
 
-int hbn_history_set_limit(char *object, int max_lines, long max_time)
+int hbn_history_set_limit(const char *object, int max_lines, long max_time)
 {
 	return 1;
 }
 
-int hbn_history_destroy(char *object)
+int hbn_history_destroy(const char *object)
 {
 	return 1;
 }
diff --git a/src/modules/json-log-tag.c b/src/modules/json-log-tag.c
index 3a304799e..5354ef1bc 100644
--- a/src/modules/json-log-tag.c
+++ b/src/modules/json-log-tag.c
@@ -35,7 +35,7 @@ ModuleHeader MOD_HEADER
 long CAP_JSON_LOG = 0L;
 
 /* Forward declarations */
-int json_log_mtag_is_ok(Client *client, char *name, char *value);
+int json_log_mtag_is_ok(Client *client, const char *name, const char *value);
 int json_log_mtag_should_send_to_client(Client *target);
 
 MOD_INIT()
@@ -73,7 +73,7 @@ MOD_UNLOAD()
 /** This function verifies if the client sending
  * We simply allow from servers without any syntax checking.
  */
-int json_log_mtag_is_ok(Client *client, char *name, char *value)
+int json_log_mtag_is_ok(Client *client, const char *name, const char *value)
 {
 	if (IsServer(client) || IsMe(client))
 		return 1;
diff --git a/src/modules/labeled-response.c b/src/modules/labeled-response.c
index 9b9088a84..5027fe08d 100644
--- a/src/modules/labeled-response.c
+++ b/src/modules/labeled-response.c
@@ -61,7 +61,7 @@ static long CAP_LABELED_RESPONSE = 0L;
 
 static char packet[8192];
 
-int labeled_response_mtag_is_ok(Client *client, char *name, char *value);
+int labeled_response_mtag_is_ok(Client *client, const char *name, const char *value);
 
 MOD_TEST()
 {
@@ -336,7 +336,7 @@ int lr_packet(Client *from, Client *to, Client *intended_to, char **msg, int *le
 /** This function verifies if the client sending the
  * tag is permitted to do so and uses a permitted syntax.
  */
-int labeled_response_mtag_is_ok(Client *client, char *name, char *value)
+int labeled_response_mtag_is_ok(Client *client, const char *name, const char *value)
 {
 	if (BadPtr(value))
 		return 0;
diff --git a/src/modules/message-ids.c b/src/modules/message-ids.c
index 27609ec6f..ec44b8c9e 100644
--- a/src/modules/message-ids.c
+++ b/src/modules/message-ids.c
@@ -34,7 +34,7 @@ ModuleHeader MOD_HEADER
 /* Variables */
 long CAP_ACCOUNT_TAG = 0L;
 
-int msgid_mtag_is_ok(Client *client, char *name, char *value);
+int msgid_mtag_is_ok(Client *client, const char *name, const char *value);
 void mtag_add_or_inherit_msgid(Client *sender, MessageTag *recv_mtags, MessageTag **mtag_list, const char *signature);
 
 MOD_INIT()
@@ -69,7 +69,7 @@ MOD_UNLOAD()
  * syntax.
  * We simply allow msgid ONLY from servers and with any syntax.
  */
-int msgid_mtag_is_ok(Client *client, char *name, char *value)
+int msgid_mtag_is_ok(Client *client, const char *name, const char *value)
 {
 	if (IsServer(client) && !BadPtr(value))
 		return 1;
diff --git a/src/modules/message-tags.c b/src/modules/message-tags.c
index 118009978..93f1caa35 100644
--- a/src/modules/message-tags.c
+++ b/src/modules/message-tags.c
@@ -32,14 +32,14 @@ ModuleHeader MOD_HEADER
 	};
 
 long CAP_MESSAGE_TAGS = 0L;
-char *_mtags_to_string(MessageTag *m, Client *client);
+const char *_mtags_to_string(MessageTag *m, Client *client);
 void _parse_message_tags(Client *client, char **str, MessageTag **mtag_list);
 
 MOD_TEST()
 {
 	MARK_AS_OFFICIAL_MODULE(modinfo);
 
-	EfunctionAddString(modinfo->handle, EFUNC_MTAGS_TO_STRING, _mtags_to_string);
+	EfunctionAddConstString(modinfo->handle, EFUNC_MTAGS_TO_STRING, _mtags_to_string);
 	EfunctionAddVoid(modinfo->handle, EFUNC_PARSE_MESSAGE_TAGS, _parse_message_tags);
 
 	return 0;
@@ -263,7 +263,7 @@ int client_accepts_tag(const char *token, Client *client)
  * Taking into account the restrictions that 'client' may have.
  * @returns A string (static buffer) or NULL if no tags at all (!)
  */
-char *_mtags_to_string(MessageTag *m, Client *client)
+const char *_mtags_to_string(MessageTag *m, Client *client)
 {
 	static char buf[4096], name[8192], value[8192];
 	static char tbuf[4094];
diff --git a/src/modules/reply-tag.c b/src/modules/reply-tag.c
index 0ad2a9749..ef9e295dd 100644
--- a/src/modules/reply-tag.c
+++ b/src/modules/reply-tag.c
@@ -33,7 +33,7 @@ ModuleHeader MOD_HEADER
 	"unrealircd-6",
 	};
 
-int replytag_mtag_is_ok(Client *client, char *name, char *value);
+int replytag_mtag_is_ok(Client *client, const char *name, const char *value);
 void mtag_add_replytag(Client *client, MessageTag *recv_mtags, MessageTag **mtag_list, const char *signature);
 
 MOD_INIT()
@@ -73,9 +73,9 @@ MOD_UNLOAD()
 
 /** This function verifies if the client sending the mtag is permitted to do so.
  */
-int replytag_mtag_is_ok(Client *client, char *name, char *value)
+int replytag_mtag_is_ok(Client *client, const char *name, const char *value)
 {
-	char *p;
+	const char *p;
 
 	/* Require a non-empty parameter */
 	if (BadPtr(value))
diff --git a/src/modules/server-time.c b/src/modules/server-time.c
index ad6b78d89..7116977df 100644
--- a/src/modules/server-time.c
+++ b/src/modules/server-time.c
@@ -34,7 +34,7 @@ ModuleHeader MOD_HEADER
 /* Variables */
 long CAP_SERVER_TIME = 0L;
 
-int server_time_mtag_is_ok(Client *client, char *name, char *value);
+int server_time_mtag_is_ok(Client *client, const char *name, const char *value);
 void mtag_add_or_inherit_time(Client *sender, MessageTag *recv_mtags, MessageTag **mtag_list, const char *signature);
 
 MOD_INIT()
@@ -75,7 +75,7 @@ MOD_UNLOAD()
  * syntax.
  * We simply allow server-time ONLY from servers.
  */
-int server_time_mtag_is_ok(Client *client, char *name, char *value)
+int server_time_mtag_is_ok(Client *client, const char *name, const char *value)
 {
 	if (IsServer(client) && !BadPtr(value))
 		return 1;
diff --git a/src/modules/typing-indicator.c b/src/modules/typing-indicator.c
index 33c86f65b..76f0320f4 100644
--- a/src/modules/typing-indicator.c
+++ b/src/modules/typing-indicator.c
@@ -31,7 +31,7 @@ ModuleHeader MOD_HEADER
 	"unrealircd-6",
 	};
 
-int ti_mtag_is_ok(Client *client, char *name, char *value);
+int ti_mtag_is_ok(Client *client, const char *name, const char *value);
 void mtag_add_ti(Client *client, MessageTag *recv_mtags, MessageTag **mtag_list, const char *signature);
 
 MOD_INIT()
@@ -69,7 +69,7 @@ MOD_UNLOAD()
 
 /** This function verifies if the client sending the mtag is permitted to do so.
  */
-int ti_mtag_is_ok(Client *client, char *name, char *value)
+int ti_mtag_is_ok(Client *client, const char *name, const char *value)
 {
 	/* Require a non-empty parameter */
 	if (BadPtr(value))
diff --git a/src/modules/userhost-tag.c b/src/modules/userhost-tag.c
index 7411adc2b..26a84a635 100644
--- a/src/modules/userhost-tag.c
+++ b/src/modules/userhost-tag.c
@@ -34,7 +34,7 @@ ModuleHeader MOD_HEADER
 /* Variables */
 long CAP_ACCOUNT_TAG = 0L;
 
-int userhost_mtag_is_ok(Client *client, char *name, char *value);
+int userhost_mtag_is_ok(Client *client, const char *name, const char *value);
 int userhost_mtag_should_send_to_client(Client *target);
 void mtag_add_userhost(Client *client, MessageTag *recv_mtags, MessageTag **mtag_list, const char *signature);
 
@@ -71,7 +71,7 @@ MOD_UNLOAD()
  * syntax.
  * We simply allow userhost-tag ONLY from servers and with any syntax.
  */
-int userhost_mtag_is_ok(Client *client, char *name, char *value)
+int userhost_mtag_is_ok(Client *client, const char *name, const char *value)
 {
 	if (IsServer(client))
 		return 1;
diff --git a/src/modules/userip-tag.c b/src/modules/userip-tag.c
index 7440e3e6e..3fba6b9e9 100644
--- a/src/modules/userip-tag.c
+++ b/src/modules/userip-tag.c
@@ -34,7 +34,7 @@ ModuleHeader MOD_HEADER
 /* Variables */
 long CAP_ACCOUNT_TAG = 0L;
 
-int userip_mtag_is_ok(Client *client, char *name, char *value);
+int userip_mtag_is_ok(Client *client, const char *name, const char *value);
 int userip_mtag_should_send_to_client(Client *target);
 void mtag_add_userip(Client *client, MessageTag *recv_mtags, MessageTag **mtag_list, const char *signature);
 
@@ -71,7 +71,7 @@ MOD_UNLOAD()
  * syntax.
  * We simply allow userip-tag ONLY from servers and with any syntax.
  */
-int userip_mtag_is_ok(Client *client, char *name, char *value)
+int userip_mtag_is_ok(Client *client, const char *name, const char *value)
 {
 	if (IsServer(client))
 		return 1;
diff --git a/src/send.c b/src/send.c
index bc3b503ae..6b49da821 100644
--- a/src/send.c
+++ b/src/send.c
@@ -216,7 +216,7 @@ void sendto_one(Client *to, MessageTag *mtags, FORMAT_STRING(const char *pattern
  */
 void vsendto_one(Client *to, MessageTag *mtags, const char *pattern, va_list vl)
 {
-	char *mtags_str = mtags ? mtags_to_string(mtags, to) : NULL;
+	const char *mtags_str = mtags ? mtags_to_string(mtags, to) : NULL;
 
 	ircvsnprintf(sendbuf, sizeof(sendbuf), pattern, vl);
 
@@ -1029,7 +1029,7 @@ void sendto_prefix_one(Client *to, Client *from, MessageTag *mtags, FORMAT_STRIN
  */
 void vsendto_prefix_one(Client *to, Client *from, MessageTag *mtags, const char *pattern, va_list vl)
 {
-	char *mtags_str = mtags ? mtags_to_string(mtags, to) : NULL;
+	const char *mtags_str = mtags ? mtags_to_string(mtags, to) : NULL;
 
 	if (to && from && MyUser(to) && from->user)
 		vmakebuf_local_withprefix(sendbuf, sizeof sendbuf, from, pattern, vl);