diff --git a/contracts/sfc/SFC.sol b/contracts/sfc/SFC.sol
index 5a3aa63..66d3d99 100644
--- a/contracts/sfc/SFC.sol
+++ b/contracts/sfc/SFC.sol
@@ -138,7 +138,7 @@ contract SFC is SFCBase, Version {
             bytes memory pubkey = getValidatorPubkey[vid];
             if (pubkey.length > 0 && pubkeyHashToValidatorID[keccak256(pubkey)] != vid) {
                 if (pubkeyHashToValidatorID[keccak256(pubkey)] != 0) {
-                    revert PubkeyExists();
+                    revert PubkeyUsedByOtherValidator();
                 }
                 pubkeyHashToValidatorID[keccak256(pubkey)] = vid;
             }
@@ -154,13 +154,13 @@ contract SFC is SFCBase, Version {
             revert ValidatorNotExists();
         }
         if (keccak256(pubkey) == keccak256(getValidatorPubkey[validatorID])) {
-            revert SamePubkey();
+            revert PubkeyNotChanged();
         }
         if (pubkeyHashToValidatorID[keccak256(pubkey)] != 0) {
-            revert PubkeyExists();
+            revert PubkeyUsedByOtherValidator();
         }
         if (validatorPubkeyChanges[validatorID] != 0) {
-            revert PubkeyAllowedOnlyOnce();
+            revert TooManyPubkeyUpdates();
         }
 
         validatorPubkeyChanges[validatorID]++;
@@ -187,7 +187,7 @@ contract SFC is SFCBase, Version {
             revert NotAuthorized();
         }
         if (getRedirection[from] == to) {
-            revert RequestedCompleted();
+            revert AlreadyRedirected();
         }
         if (from == to) {
             revert SameAddress();
diff --git a/contracts/sfc/SFCBase.sol b/contracts/sfc/SFCBase.sol
index 164404f..4c46db0 100644
--- a/contracts/sfc/SFCBase.sol
+++ b/contracts/sfc/SFCBase.sol
@@ -24,11 +24,11 @@ contract SFCBase is SFCState {
     error ZeroRewards();
 
     // pubkeys
-    error PubkeyExists();
+    error PubkeyUsedByOtherValidator();
     error MalformedPubkey();
-    error SamePubkey();
+    error PubkeyNotChanged();
     error EmptyPubkey();
-    error PubkeyAllowedOnlyOnce();
+    error TooManyPubkeyUpdates();
 
     // redirections
     error SameRedirectionAuthorizer();
@@ -42,7 +42,7 @@ contract SFCBase is SFCState {
     error WrongValidatorStatus();
 
     // requests
-    error RequestedCompleted();
+    error AlreadyRedirected();
     error RequestExists();
     error RequestNotExists();
 
diff --git a/contracts/sfc/SFCLib.sol b/contracts/sfc/SFCLib.sol
index 47e1f36..debc464 100644
--- a/contracts/sfc/SFCLib.sol
+++ b/contracts/sfc/SFCLib.sol
@@ -103,7 +103,7 @@ contract SFCLib is SFCBase {
             revert EmptyPubkey();
         }
         if (pubkeyHashToValidatorID[keccak256(pubkey)] != 0) {
-            revert PubkeyExists();
+            revert PubkeyUsedByOtherValidator();
         }
         _createValidator(msg.sender, pubkey);
         _delegate(msg.sender, lastValidatorID, msg.value);
diff --git a/contracts/sfc/SFCState.sol b/contracts/sfc/SFCState.sol
index e19fadd..6a961f0 100644
--- a/contracts/sfc/SFCState.sol
+++ b/contracts/sfc/SFCState.sol
@@ -14,10 +14,10 @@ contract SFCState is Initializable, Ownable {
         uint256 status;
         uint256 deactivatedTime;
         uint256 deactivatedEpoch;
-        uint256 receivedStake;
+        uint256 receivedStake; // from all delegators (weight of the validator)
         uint256 createdEpoch;
         uint256 createdTime;
-        address auth;
+        address auth; // self-stake delegator
     }
 
     NodeDriverAuth internal node;
@@ -28,26 +28,34 @@ contract SFCState is Initializable, Ownable {
         uint256 unlockedReward;
     }
 
+    // last sealed epoch (currentEpoch - 1)
     uint256 public currentSealedEpoch;
     mapping(uint256 => Validator) public getValidator;
     mapping(address => uint256) public getValidatorID;
     mapping(uint256 => bytes) public getValidatorPubkey;
 
     uint256 public lastValidatorID;
+
+    // total stake of all validators - includes slashed/offline validators
     uint256 public totalStake;
+    // total stake of active (OK_STATUS) validators (total weight)
     uint256 public totalActiveStake;
+    // sum of penalties subtracted from successful withdrawals - TODO misleading - remove?
     uint256 public totalSlashedStake;
 
-    mapping(address => mapping(uint256 => Rewards)) internal _rewardsStash; // addr, validatorID -> Rewards
+    // delegator => validator ID => stashed rewards (to be claimed/restaked)
+    mapping(address => mapping(uint256 => Rewards)) internal _rewardsStash;
 
+    // delegator => validator ID => last epoch number for which were rewards stashed
     mapping(address => mapping(uint256 => uint256)) public stashedRewardsUntilEpoch;
 
     struct WithdrawalRequest {
-        uint256 epoch;
-        uint256 time;
+        uint256 epoch; // epoch where undelegated
+        uint256 time; // when undelegated
         uint256 amount;
     }
 
+    // delegator => validator ID => withdrawal ID => withdrawal request
     mapping(address => mapping(uint256 => mapping(uint256 => WithdrawalRequest))) public getWithdrawalRequest;
 
     struct LockedDelegation {
@@ -57,43 +65,56 @@ contract SFCState is Initializable, Ownable {
         uint256 duration;
     }
 
+    // delegator => validator ID => current stake (locked+unlocked)
     mapping(address => mapping(uint256 => uint256)) public getStake;
 
+    // delegator => validator ID => locked stake info
     mapping(address => mapping(uint256 => LockedDelegation)) public getLockupInfo;
 
     mapping(address => mapping(uint256 => Rewards)) public getStashedLockupRewards;
 
     struct EpochSnapshot {
+        // validator ID => validator weight in the epoch
         mapping(uint256 => uint256) receivedStake;
+        // validator ID => accumulated ( delegatorsReward * 1e18 / receivedStake )
         mapping(uint256 => uint256) accumulatedRewardPerToken;
+        // validator ID => accumulated online time
         mapping(uint256 => uint256) accumulatedUptime;
+        // validator ID => gas fees from txs originated by the validator
         mapping(uint256 => uint256) accumulatedOriginatedTxsFee;
         mapping(uint256 => uint256) offlineTime;
         mapping(uint256 => uint256) offlineBlocks;
         uint256[] validatorIDs;
         uint256 endTime;
         uint256 endBlock;
-        uint256 epochFee;
-        uint256 totalBaseRewardWeight;
-        uint256 totalTxRewardWeight;
-        uint256 baseRewardPerSecond;
-        uint256 totalStake;
-        uint256 totalSupply;
+        uint256 epochFee; // gas fees from txs in the epoch
+        uint256 totalBaseRewardWeight; // sum( stake * uptimeRatio ^ 2 ) TODO write only - remove?
+        uint256 totalTxRewardWeight; // sum( originatedTxsFee * uptimeRatio ) TODO write only - remove?
+        uint256 baseRewardPerSecond; // the base reward to divide among validators for each second of the epoch
+        uint256 totalStake; // total weight of all validators
+        uint256 totalSupply; // total supply of native tokens
     }
 
+    // the total supply of native tokens in the chain
     uint256 public totalSupply;
+    // epoch id => epoch snapshot
     mapping(uint256 => EpochSnapshot) public getEpochSnapshot;
 
-    mapping(uint256 => uint256) public slashingRefundRatio; // validator ID -> (slashing refund ratio)
+    // validator ID -> slashing refund ratio (allows to withdraw slashed stake)
+    mapping(uint256 => uint256) public slashingRefundRatio;
 
+    // the minimal gas price calculated for the current epoch
     uint256 public minGasPrice;
 
+    // the treasure contract (receives unlock penalties and a part of epoch fees)
     address public treasuryAddress;
 
+    // the SFCLib contract
     address internal libAddress;
 
     ConstantsManager internal c;
 
+    // the governance contract (to recalculate votes when a stake changes)
     address public voteBookAddress;
 
     struct Penalty {
@@ -103,13 +124,18 @@ contract SFCState is Initializable, Ownable {
     // delegator => validatorID => penalties info
     mapping(address => mapping(uint256 => Penalty[])) public getStashedPenalties;
 
+    // validator ID => amount of pubkey updates
     mapping(uint256 => uint256) internal validatorPubkeyChanges;
 
+    // keccak256(pubkey bytes) => validator ID (prevents using the same key by multiple validators)
     mapping(bytes32 => uint256) internal pubkeyHashToValidatorID;
 
+    // address authorized to initiate redirection
     address public redirectionAuthorizer;
 
+    // delegator => withdrawals/claims receiver
     mapping(address => address) public getRedirectionRequest;
 
+    // delegator => withdrawals/claims receiver
     mapping(address => address) public getRedirection;
 }