diff --git a/bridges/relays/lib-substrate-relay/src/finality_pipeline.rs b/bridges/relays/lib-substrate-relay/src/finality_pipeline.rs
index deb83d4ea9..2dc9a63947 100644
--- a/bridges/relays/lib-substrate-relay/src/finality_pipeline.rs
+++ b/bridges/relays/lib-substrate-relay/src/finality_pipeline.rs
@@ -35,6 +35,7 @@ pub(crate) const RECENT_FINALITY_PROOFS_LIMIT: usize = 4096;
 
 /// Headers sync pipeline for Substrate <-> Substrate relays.
 pub trait SubstrateFinalitySyncPipeline: 'static + Clone + Debug + Send + Sync {
+	/// Pipeline for syncing finalized Source chain headers to Target chain.
 	type FinalitySyncPipeline: FinalitySyncPipeline;
 
 	/// Name of the runtime method that returns id of best finalized source header at target chain.
diff --git a/bridges/relays/lib-substrate-relay/src/messages_lane.rs b/bridges/relays/lib-substrate-relay/src/messages_lane.rs
index fae07c33b3..15b75ae945 100644
--- a/bridges/relays/lib-substrate-relay/src/messages_lane.rs
+++ b/bridges/relays/lib-substrate-relay/src/messages_lane.rs
@@ -14,6 +14,8 @@
 // You should have received a copy of the GNU General Public License
 // along with Parity Bridges Common.  If not, see <http://www.gnu.org/licenses/>.
 
+//! Tools for supporting message lanes between two Substrate-based chains.
+
 use crate::messages_source::SubstrateMessagesProof;
 use crate::messages_target::SubstrateMessagesReceivingProof;
 use crate::on_demand_headers::OnDemandHeadersRelay;
@@ -57,6 +59,7 @@ pub struct MessagesRelayParams<SC: Chain, SS, TC: Chain, TS> {
 
 /// Message sync pipeline for Substrate <-> Substrate relays.
 pub trait SubstrateMessageLane: 'static + Clone + Send + Sync {
+	/// Underlying generic message lane.
 	type MessageLane: MessageLane;
 
 	/// Name of the runtime method that returns dispatch weight of outbound messages at the source chain.
diff --git a/bridges/relays/lib-substrate-relay/src/messages_source.rs b/bridges/relays/lib-substrate-relay/src/messages_source.rs
index 279b2c45e0..08e4964de7 100644
--- a/bridges/relays/lib-substrate-relay/src/messages_source.rs
+++ b/bridges/relays/lib-substrate-relay/src/messages_source.rs
@@ -298,6 +298,11 @@ fn prepare_dummy_messages_delivery_proof<SC: Chain, TC: Chain>() -> SubstrateMes
 	)
 }
 
+/// Read best blocks from given client.
+///
+/// This function assumes that the chain that is followed by the `self_client` has
+/// bridge GRANDPA pallet deployed and it provides `best_finalized_header_id_method_name`
+/// runtime API to read best finalized Bridged chain header.
 pub async fn read_client_state<SelfChain, BridgedHeaderHash, BridgedHeaderNumber>(
 	self_client: &Client<SelfChain>,
 	best_finalized_header_id_method_name: &str,