diff --git a/core/client/src/lib.rs b/core/client/src/lib.rs
index 8062fae500199..f5d1298f941bb 100644
--- a/core/client/src/lib.rs
+++ b/core/client/src/lib.rs
@@ -35,6 +35,7 @@ pub mod in_mem;
 #[cfg(feature = "std")]
 pub mod genesis;
 pub mod block_builder;
+pub mod transaction_builder;
 #[cfg(feature = "std")]
 pub mod light;
 #[cfg(feature = "std")]
diff --git a/core/client/src/transaction_builder.rs b/core/client/src/transaction_builder.rs
new file mode 100644
index 0000000000000..700de8c4c7456
--- /dev/null
+++ b/core/client/src/transaction_builder.rs
@@ -0,0 +1,40 @@
+// Copyright 2019 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! The runtime api for building transactions.
+
+use sr_api_macros::decl_runtime_apis;
+use runtime_primitives::KeyTypeId;
+use rstd::vec::Vec;
+
+decl_runtime_apis! {
+	/// The `TransactionBuilder` trait that provides required functions
+	/// for building a transaction from a Call for the runtime.
+	pub trait TransactionBuilder {
+		/// Construct the payload.
+		fn signing_payload(encoded_call: Vec<u8>, encoded_account_id: Vec<u8>) -> Vec<u8>;
+
+		/// Build the transaction.
+		fn build_transaction(
+			signing_payload: Vec<u8>,
+			encoded_account_id: Vec<u8>,
+			signature: Vec<u8>,
+		) -> Vec<u8>;
+
+		/// Get list of supported crypto types.
+		fn possible_crypto() -> Vec<KeyTypeId>;
+	}
+}