diff --git a/lightningd/jsonrpc.c b/lightningd/jsonrpc.c
index 558e581bd..06f6e4a86 100644
--- a/lightningd/jsonrpc.c
+++ b/lightningd/jsonrpc.c
@@ -442,6 +442,7 @@ static void parse_request(struct json_connection *jcon, const jsmntok_t tok[])
 	c->id = tal_strndup(c,
 			    json_tok_contents(jcon->buffer, id),
 			    json_tok_len(id));
+	c->mode = CMD_NORMAL;
 	list_add(&jcon->commands, &c->list);
 	tal_add_destructor(c, destroy_cmd);
 
diff --git a/lightningd/jsonrpc.h b/lightningd/jsonrpc.h
index 9f36b8010..e155258a2 100644
--- a/lightningd/jsonrpc.h
+++ b/lightningd/jsonrpc.h
@@ -10,6 +10,14 @@ struct bitcoin_txid;
 struct wireaddr;
 struct wallet_tx;
 
+/* The command mode tells param() how to process. */
+enum command_mode {
+	/* Normal command processing */
+	CMD_NORMAL,
+	/* Create command usage string, nothing else. */
+	CMD_USAGE
+};
+
 /* Context for a command (from JSON, but might outlive the connection!)
  * You can allocate off this for temporary objects. */
 struct command {
@@ -25,6 +33,10 @@ struct command {
 	struct json_connection *jcon;
 	/* Have we been marked by command_still_pending?  For debugging... */
 	bool pending;
+	/* Tell param() how to process the command */
+	enum command_mode mode;
+	/* This is created if mode is CMD_USAGE */
+	const char *usage;
 };
 
 struct json_connection {
diff --git a/lightningd/param.c b/lightningd/param.c
index a20c00938..c1480d7a5 100644
--- a/lightningd/param.c
+++ b/lightningd/param.c
@@ -223,6 +223,21 @@ static bool check_params(struct param *params)
 }
 #endif
 
+static char *param_usage(const tal_t *ctx,
+			 const struct param *params)
+{
+	char *usage = tal_strdup(ctx, "");
+	for (size_t i = 0; i < tal_count(params); i++) {
+		if (i != 0)
+			tal_append_fmt(&usage, " ");
+		if (params[i].required)
+			tal_append_fmt(&usage, "%s", params[i].name);
+		else
+			tal_append_fmt(&usage, "[%s]", params[i].name);
+	}
+	return usage;
+}
+
 static bool param_arr(struct command *cmd, const char *buffer,
 		      const jsmntok_t tokens[],
 		      struct param *params)
@@ -263,5 +278,10 @@ bool param(struct command *cmd, const char *buffer,
 	}
 	va_end(ap);
 
+	if (cmd->mode == CMD_USAGE) {
+		cmd->usage = param_usage(cmd, params);
+		return false;
+	}
+
 	return param_arr(cmd, buffer, tokens, params);
 }
diff --git a/lightningd/test/run-param.c b/lightningd/test/run-param.c
index 033ec56dd..7b069deb0 100644
--- a/lightningd/test/run-param.c
+++ b/lightningd/test/run-param.c
@@ -431,7 +431,7 @@ static void advanced(void)
 			     p_opt("msat_opt2", json_tok_msat, &msat_opt2),
 			     NULL));
 		assert(label != NULL);
-		assert(!strcmp(label->s, "lightning"));
+		assert(streq(label->s, "lightning"));
 		assert(*msat == 24);
 		assert(tok);
 		assert(msat_opt1);
@@ -445,8 +445,8 @@ static void advanced(void)
 			      p_req("label", json_tok_label, &label),
 			      p_opt("foo", json_tok_label, &foo),
 			      NULL));
-		assert(!strcmp(label->s, "3"));
-		assert(!strcmp(foo->s, "foo"));
+		assert(streq(label->s, "3"));
+		assert(streq(foo->s, "foo"));
 	}
 	{
 		u64 *msat;
@@ -507,6 +507,54 @@ static void json_tok_tests(void)
 	test_cb(json_tok_percent, double, "[ 'wow' ]", 0, false);
 }
 
+static void test_invoice(struct command *cmd, const char *buffer,
+			 const jsmntok_t *params)
+{
+	u64 *msatoshi_val;
+	struct json_escaped *label_val;
+	const char *desc_val;
+	u64 *expiry;
+	const jsmntok_t *fallbacks;
+	const jsmntok_t *preimagetok;
+
+	assert(cmd->mode == CMD_USAGE);
+	if(!param(cmd, buffer, params,
+		  p_req("msatoshi", json_tok_msat, &msatoshi_val),
+		  p_req("label", json_tok_label, &label_val),
+		  p_req("description", json_tok_escaped_string, &desc_val),
+		  p_opt("expiry", json_tok_u64, &expiry),
+		  p_opt("fallbacks", json_tok_array, &fallbacks),
+		  p_opt("preimage", json_tok_tok, &preimagetok), NULL))
+		return;
+
+	/* should not be here since we are in the mode of CMD_USAGE
+	 * and it always returns false. */
+	abort();
+}
+
+static void usage(void)
+{
+	/* Do this to simulate a call to our pretend handler (test_invoice) */
+	struct json_command invoice_command = {
+		"invoice",
+		test_invoice,
+		"",
+		false,
+		""
+	};
+
+	cmd->mode = CMD_USAGE;
+	cmd->json_cmd = &invoice_command;
+
+	cmd->json_cmd->dispatch(cmd, NULL, NULL);
+
+	assert(streq(cmd->usage,
+		     "msatoshi label description "
+		     "[expiry] [fallbacks] [preimage]"));
+
+	cmd->mode = CMD_NORMAL;
+}
+
 int main(void)
 {
 	setup_locale();
@@ -528,6 +576,8 @@ int main(void)
 	advanced();
 	advanced_fail();
 	json_tok_tests();
+	usage();
+
 	tal_free(tmpctx);
 	printf("run-params ok\n");
 }