diff --git a/common/json_command.h b/common/json_command.h
index 8cbfc4db4..f703bcd74 100644
--- a/common/json_command.h
+++ b/common/json_command.h
@@ -39,6 +39,9 @@ bool command_usage_only(const struct command *cmd);
 /* Do we allow deprecated apis? */
 bool command_deprecated_apis(const struct command *cmd);
 
+/* Do we allow dev commands? */
+bool command_dev_apis(const struct command *cmd);
+
 /* If so, this is called. */
 void command_set_usage(struct command *cmd, const char *usage);
 
diff --git a/common/json_param.c b/common/json_param.c
index 82d2594a1..dc302b00d 100644
--- a/common/json_param.c
+++ b/common/json_param.c
@@ -65,7 +65,9 @@ static struct command_result *make_callback(struct command *cmd,
 					     const jsmntok_t *tok)
 {
 	/* If it had a default, free that now to avoid leak */
-	if (def->style == PARAM_OPTIONAL_WITH_DEFAULT && !def->is_set)
+	if ((def->style == PARAM_OPTIONAL_WITH_DEFAULT
+	     || def->style == PARAM_OPTIONAL_DEV_WITH_DEFAULT)
+	    && !def->is_set)
 		tal_free(*(void **)def->arg);
 
 	def->is_set = true;
@@ -115,6 +117,11 @@ static struct command_result *parse_by_position(struct command *cmd,
 		}
 
 		if (!json_tok_is_null(buffer, tok)) {
+			if (params[i].style == PARAM_OPTIONAL_DEV_WITH_DEFAULT
+			    && !command_dev_apis(cmd)) {
+				return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+						    "Parameter %zu is developer-only", i);
+			}
 			res = make_callback(cmd, params+i, buffer, tok);
 			if (res)
 				return res;
@@ -176,6 +183,12 @@ static struct command_result *parse_by_name(struct command *cmd,
 						    p->name);
 			}
 
+			if (p->style == PARAM_OPTIONAL_DEV_WITH_DEFAULT
+			    && !command_dev_apis(cmd)) {
+				return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+						    "Parameter '%s' is developer-only",
+						    p->name);
+			}
 			res = make_callback(cmd, p, buffer, t + 1);
 			if (res)
 				return res;
diff --git a/common/json_param.h b/common/json_param.h
index f920791cd..fa37dfd03 100644
--- a/common/json_param.h
+++ b/common/json_param.h
@@ -78,6 +78,7 @@ enum param_style {
 	PARAM_REQUIRED_ALLOW_DUPS,
 	PARAM_OPTIONAL,
 	PARAM_OPTIONAL_WITH_DEFAULT,
+	PARAM_OPTIONAL_DEV_WITH_DEFAULT,
 };
 
 /*
@@ -136,6 +137,21 @@ enum param_style {
 				   (const jsmntok_t *)NULL,	    \
 				   (arg)) == (struct command_result *)NULL); })
 
+/*
+ * Add a dev-only parameter.  *arg is set to @def if it isn't found.
+ */
+#define p_opt_dev(name, cbx, arg, def)				    \
+		  name"",					    \
+		  PARAM_OPTIONAL_DEV_WITH_DEFAULT,		    \
+		  (param_cbx)(cbx),				    \
+		  ({ (*arg) = tal((cmd), typeof(**arg));            \
+		     (**arg) = (def);                               \
+		     (arg) + 0*sizeof((cbx)((struct command *)NULL, \
+				   (const char *)NULL,		    \
+				   (const char *)NULL,		    \
+				   (const jsmntok_t *)NULL,	    \
+				   (arg)) == (struct command_result *)NULL); })
+
 /* Special flag for 'check' which allows any parameters. */
 #define p_opt_any() "", PARAM_OPTIONAL, NULL, NULL
 
diff --git a/common/test/run-json_filter.c b/common/test/run-json_filter.c
index 58be0ca0c..4c31e1550 100644
--- a/common/test/run-json_filter.c
+++ b/common/test/run-json_filter.c
@@ -18,6 +18,9 @@ bool command_check_only(const struct command *cmd UNNEEDED)
 /* Generated stub for command_deprecated_apis */
 bool command_deprecated_apis(const struct command *cmd UNNEEDED)
 { fprintf(stderr, "command_deprecated_apis called!\n"); abort(); }
+/* Generated stub for command_dev_apis */
+bool command_dev_apis(const struct command *cmd UNNEEDED)
+{ fprintf(stderr, "command_dev_apis called!\n"); abort(); }
 /* Generated stub for command_fail */
 struct command_result *command_fail(struct command *cmd UNNEEDED, enum jsonrpc_errcode code UNNEEDED,
 				    const char *fmt UNNEEDED, ...)
diff --git a/common/test/run-json_remove.c b/common/test/run-json_remove.c
index 64e246e00..120009514 100644
--- a/common/test/run-json_remove.c
+++ b/common/test/run-json_remove.c
@@ -50,6 +50,9 @@ bool command_check_only(const struct command *cmd UNNEEDED)
 /* Generated stub for command_deprecated_apis */
 bool command_deprecated_apis(const struct command *cmd UNNEEDED)
 { fprintf(stderr, "command_deprecated_apis called!\n"); abort(); }
+/* Generated stub for command_dev_apis */
+bool command_dev_apis(const struct command *cmd UNNEEDED)
+{ fprintf(stderr, "command_dev_apis called!\n"); abort(); }
 /* Generated stub for command_fail */
 struct command_result *command_fail(struct command *cmd UNNEEDED, enum jsonrpc_errcode code UNNEEDED,
 				    const char *fmt UNNEEDED, ...)
diff --git a/common/test/run-param.c b/common/test/run-param.c
index 6ee699a29..b62c838a6 100644
--- a/common/test/run-param.c
+++ b/common/test/run-param.c
@@ -49,6 +49,9 @@ struct command_result *command_fail(struct command *cmd,
 }
 
 /* AUTOGENERATED MOCKS START */
+/* Generated stub for command_dev_apis */
+bool command_dev_apis(const struct command *cmd UNNEEDED)
+{ fprintf(stderr, "command_dev_apis called!\n"); abort(); }
 /* Generated stub for command_filter_ptr */
 struct json_filter **command_filter_ptr(struct command *cmd UNNEEDED)
 { fprintf(stderr, "command_filter_ptr called!\n"); abort(); }
diff --git a/lightningd/jsonrpc.c b/lightningd/jsonrpc.c
index f12d2e2bd..3e1a696f9 100644
--- a/lightningd/jsonrpc.c
+++ b/lightningd/jsonrpc.c
@@ -1295,6 +1295,11 @@ bool command_deprecated_apis(const struct command *cmd)
 	return cmd->ld->deprecated_apis;
 }
 
+bool command_dev_apis(const struct command *cmd)
+{
+	return cmd->ld->developer;
+}
+
 void command_set_usage(struct command *cmd, const char *usage TAKES)
 {
 	usage = tal_strdup(cmd->ld, usage);
diff --git a/plugins/libplugin.c b/plugins/libplugin.c
index aa3eb9a43..f049d2759 100644
--- a/plugins/libplugin.c
+++ b/plugins/libplugin.c
@@ -505,6 +505,11 @@ bool command_deprecated_apis(const struct command *cmd)
 	return deprecated_apis;
 }
 
+bool command_dev_apis(const struct command *cmd)
+{
+	return cmd->plugin->developer;
+}
+
 /* FIXME: would be good to support this! */
 bool command_check_only(const struct command *cmd)
 {
diff --git a/plugins/renepay/payment.c b/plugins/renepay/payment.c
index 0a95ae766..465201613 100644
--- a/plugins/renepay/payment.c
+++ b/plugins/renepay/payment.c
@@ -20,7 +20,7 @@ struct payment *payment_new(const tal_t *ctx,
 				    unsigned int maxdelay,
 				    u64 retryfor,
 				    u16 final_cltv,
-				    /* Tweakable in DEVELOPER mode */
+				    /* Tweakable in --developer mode */
 				    u64 base_fee_penalty,
 				    u64 prob_cost_factor,
 				    u64 riskfactor_millionths,