diff --git a/contracts/.gitkeep b/contracts/.gitkeep
new file mode 100644
index 0000000..e69de29
diff --git a/contracts/Bucket.sol b/contracts/Bucket.sol
index e247d1f..373573b 100644
--- a/contracts/Bucket.sol
+++ b/contracts/Bucket.sol
@@ -1,7 +1,7 @@
-pragma solidity ^0.5.16;
+pragma solidity ^0.6.1;
 pragma experimental ABIEncoderV2;
 
-contract Bucket {
+abstract contract Bucket {
   bool initialized;
   address payable public owner;
   address public tokenAddress;
@@ -50,7 +50,7 @@ contract Bucket {
     startTime = _startTime;
     expirationTime = _expirationTime;
     maxTxDelayInBlocks = _maxTxDelayInBlocks;
-    owner = address(uint160(_owner));
+    owner = payable(_owner);
 
     DOMAIN_SEPARATOR = keccak256(abi.encode(
       EIP712DOMAIN_TYPEHASH,
@@ -63,11 +63,11 @@ contract Bucket {
     initialized = true;
   }
 
-  function transferRedeemable(uint256 data, Redeem memory redeem) internal;
+  function transferRedeemable(uint256 data, Redeem memory redeem) virtual internal;
 
-  function transferRedeemablesToOwner() internal;
+  function transferRedeemablesToOwner() virtual internal;
 
-  function bucketType() external returns (uint256);
+  function bucketType() virtual external returns (uint256);
 
   function redeem(Redeem calldata _redeem, bytes calldata _sig) external {
     // validate Redeem
diff --git a/contracts/ERC20Bucket.sol b/contracts/ERC20Bucket.sol
index e2c68b5..1bf1e6e 100644
--- a/contracts/ERC20Bucket.sol
+++ b/contracts/ERC20Bucket.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.5.16;
+pragma solidity ^0.6.1;
 pragma experimental ABIEncoderV2;
 
 import "./Bucket.sol";
@@ -41,18 +41,18 @@ contract ERC20Bucket is Bucket {
     redeemableSupply += amount;
   }
 
-  function transferRedeemable(uint256 data, Redeem memory redeem) internal {
+  function transferRedeemable(uint256 data, Redeem memory redeem) internal override {
     require(redeemableSupply >= data, "not enough redeemable supply");
     redeemableSupply -= data;
     IERC20(tokenAddress).transfer(redeem.receiver, data);
   }
 
-  function transferRedeemablesToOwner() internal {
+  function transferRedeemablesToOwner() internal override {
     bool success = IERC20(tokenAddress).transfer(owner, this.totalSupply());
     assert(success);
   }
 
-  function bucketType() external returns (uint256) {
+  function bucketType() external override returns (uint256) {
     return 20;
   }
 }
diff --git a/contracts/ERC20BucketFactory.sol b/contracts/ERC20BucketFactory.sol
index 95f8192..c353b3c 100644
--- a/contracts/ERC20BucketFactory.sol
+++ b/contracts/ERC20BucketFactory.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.5.16;
+pragma solidity ^0.6.1;
 
 import "./ERC20Bucket.sol";
 import "./Proxy.sol";
diff --git a/contracts/NFTBucket.sol b/contracts/NFTBucket.sol
index f536205..7969d07 100644
--- a/contracts/NFTBucket.sol
+++ b/contracts/NFTBucket.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.5.16;
+pragma solidity ^0.6.1;
 pragma experimental ABIEncoderV2;
 
 import "./Bucket.sol";
@@ -15,24 +15,24 @@ contract NFTBucket is Bucket, IERC165, IERC721Receiver {
     uint256 _expirationTime,
     uint256 _maxTxDelayInBlocks) Bucket("KeycardNFTBucket", _tokenAddress, _startTime, _expirationTime, _maxTxDelayInBlocks) public {}
 
-  function transferRedeemable(uint256 data, Redeem memory redeem) internal {
+  function transferRedeemable(uint256 data, Redeem memory redeem) internal override {
     IERC721(tokenAddress).safeTransferFrom(address(this), redeem.receiver, data);
   }
 
-  function transferRedeemablesToOwner() internal {
+  function transferRedeemablesToOwner() internal override {
     IERC721(tokenAddress).setApprovalForAll(owner, true);
     assert(IERC721(tokenAddress).isApprovedForAll(address(this), owner));
   }
 
-  function bucketType() external returns (uint256) {
+  function bucketType() external override returns (uint256) {
     return 721;
   }
 
-  function supportsInterface(bytes4 interfaceID) external view returns (bool) {
+  function supportsInterface(bytes4 interfaceID) external override(IERC165) view returns (bool) {
       return interfaceID == _ERC721_RECEIVED;
   }
 
-  function onERC721Received(address _operator, address _from, uint256 _tokenID, bytes calldata _data) external returns(bytes4) {
+  function onERC721Received(address _operator, address _from, uint256 _tokenID, bytes calldata _data) external override(IERC721Receiver) returns(bytes4) {
     require(msg.sender == tokenAddress, "only the NFT contract can call this");
     require((_operator == owner) || (_from == owner), "only the owner can create redeemables");
     require(_data.length == 52, "invalid data field");
diff --git a/contracts/NFTBucketFactory.sol b/contracts/NFTBucketFactory.sol
index 66910ca..15d7e0b 100644
--- a/contracts/NFTBucketFactory.sol
+++ b/contracts/NFTBucketFactory.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.5.16;
+pragma solidity ^0.6.1;
 
 import "./NFTBucket.sol";
 import "./Proxy.sol";
diff --git a/contracts/Proxy.sol b/contracts/Proxy.sol
index af7933f..b90e19e 100644
--- a/contracts/Proxy.sol
+++ b/contracts/Proxy.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.5.16;
+pragma solidity ^0.6.1;
 
 contract Proxy {
   /**
@@ -23,7 +23,7 @@ contract Proxy {
    * @dev Fallback function allowing to perform a delegatecall to the given implementation.
    * This function will return whatever the implementation call returns
    */
-  function() external payable {
+  fallback() external payable {
     assembly { // solium-disable-line
       let contractLogic := sload(0xc5f16f0fcc639fa48a6947836d9850f504798523bf8c9a3a87d5876cf622bcf7)
       calldatacopy(0x0, 0x0, calldatasize())
diff --git a/contracts/erc20/IERC20.sol b/contracts/erc20/IERC20.sol
index 27d3ab3..3fb727d 100644
--- a/contracts/erc20/IERC20.sol
+++ b/contracts/erc20/IERC20.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.5.16;
+pragma solidity ^0.6.1;
 
 // https://github.com/ethereum/EIPs/issues/20
 
diff --git a/contracts/erc20/IERC20Detailed.sol b/contracts/erc20/IERC20Detailed.sol
index 3865937..d76f52e 100644
--- a/contracts/erc20/IERC20Detailed.sol
+++ b/contracts/erc20/IERC20Detailed.sol
@@ -1,9 +1,9 @@
-pragma solidity ^0.5.16;
+pragma solidity >=0.5.0 <0.7.0;
 
 import "./IERC20.sol";
 
-contract IERC20Detailed is IERC20 {
-  function symbol() public view returns (string memory);
-  function decimals() public view returns (uint8);
+abstract contract IERC20Detailed is IERC20 {
+  function symbol() virtual public view returns (string memory);
+  function decimals() virtual public view returns (uint8);
 }
 
diff --git a/contracts/erc20/StandardToken.sol b/contracts/erc20/StandardToken.sol
index 9fc0b23..9c15bcf 100644
--- a/contracts/erc20/StandardToken.sol
+++ b/contracts/erc20/StandardToken.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.5.16;
+pragma solidity ^0.6.1;
 
 import "./IERC20.sol";
 
@@ -15,6 +15,7 @@ contract StandardToken is IERC20 {
         uint256 _value
     )
         external
+        override(IERC20)
         returns (bool success)
     {
         return transfer(msg.sender, _to, _value);
@@ -22,6 +23,7 @@ contract StandardToken is IERC20 {
 
     function approve(address _spender, uint256 _value)
         external
+        override(IERC20)
         returns (bool success)
     {
         allowed[msg.sender][_spender] = _value;
@@ -35,6 +37,7 @@ contract StandardToken is IERC20 {
         uint256 _value
     )
         external
+        override(IERC20)
         returns (bool success)
     {
         if (balances[_from] >= _value &&
@@ -50,6 +53,7 @@ contract StandardToken is IERC20 {
     function allowance(address _owner, address _spender)
         external
         view
+        override(IERC20)
         returns (uint256 remaining)
     {
         return allowed[_owner][_spender];
@@ -58,6 +62,7 @@ contract StandardToken is IERC20 {
     function balanceOf(address _owner)
         external
         view
+        override(IERC20)
         returns (uint256 balance)
     {
         return balances[_owner];
@@ -66,6 +71,7 @@ contract StandardToken is IERC20 {
     function totalSupply()
         external
         view
+        override(IERC20)
         returns(uint256 currentTotalSupply)
     {
         return supply;
diff --git a/contracts/erc20/TestToken.sol b/contracts/erc20/TestToken.sol
index ffe37c9..7007ca3 100644
--- a/contracts/erc20/TestToken.sol
+++ b/contracts/erc20/TestToken.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.5.16;
+pragma solidity ^0.6.1;
 
 import "./StandardToken.sol";
 
@@ -16,8 +16,7 @@ contract TestToken is StandardToken {
     _decimals = decimals;
   }
 
-  // fallback
-  function() external {
+  fallback() external {
     uint256 amount = 5000;
     mint(amount * uint256(10)**_decimals);
   }
diff --git a/contracts/erc721/IERC165.sol b/contracts/erc721/IERC165.sol
index 1874cb9..f4e686f 100644
--- a/contracts/erc721/IERC165.sol
+++ b/contracts/erc721/IERC165.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.5.16;
+pragma solidity ^0.6.1;
 
 interface IERC165 {
     function supportsInterface(bytes4 interfaceId) external view returns (bool);
diff --git a/contracts/erc721/IERC721.sol b/contracts/erc721/IERC721.sol
index a0f2538..fa09845 100644
--- a/contracts/erc721/IERC721.sol
+++ b/contracts/erc721/IERC721.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.5.16;
+pragma solidity ^0.6.1;
 
 /**
  * @dev Required interface of an ERC721 compliant contract.
@@ -22,4 +22,4 @@ interface IERC721 {
     function isApprovedForAll(address owner, address operator) external view returns (bool);
 
     function safeTransferFrom(address from, address to, uint256 tokenId, bytes calldata data) external;
-}
+}
\ No newline at end of file
diff --git a/contracts/erc721/IERC721Metadata.sol b/contracts/erc721/IERC721Metadata.sol
index 690f8c4..1c15944 100644
--- a/contracts/erc721/IERC721Metadata.sol
+++ b/contracts/erc721/IERC721Metadata.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.5.16;
+pragma solidity ^0.6.1;
 
 /// @title ERC-721 Non-Fungible Token Standard, optional metadata extension
 /// @dev See https://eips.ethereum.org/EIPS/eip-721
diff --git a/contracts/erc721/IERC721Receiver.sol b/contracts/erc721/IERC721Receiver.sol
index b854ef7..f598294 100644
--- a/contracts/erc721/IERC721Receiver.sol
+++ b/contracts/erc721/IERC721Receiver.sol
@@ -1,5 +1,5 @@
-pragma solidity ^0.5.16;
+pragma solidity ^0.6.1;
 
 interface IERC721Receiver {
     function onERC721Received(address operator, address from, uint256 tokenId, bytes calldata data) external returns (bytes4);
-}
+}
\ No newline at end of file
diff --git a/contracts/erc721/TestNFT.sol b/contracts/erc721/TestNFT.sol
index f19ede1..4289688 100644
--- a/contracts/erc721/TestNFT.sol
+++ b/contracts/erc721/TestNFT.sol
@@ -1,4 +1,4 @@
-pragma solidity ^0.5.16;
+pragma solidity ^0.6.1;
 
 import "./IERC721.sol";
 import "./IERC721Receiver.sol";
@@ -14,19 +14,19 @@ contract TestNFT is IERC165, IERC721 {
 
     bytes4 private constant _INTERFACE_ID_ERC721 = 0x80ac58cd;
 
-    function balanceOf(address owner) public view returns (uint256) {
+    function balanceOf(address owner) public override(IERC721) view returns (uint256) {
         require(owner != address(0), "ERC721: balance query for the zero address");
         return _ownedTokensCount[owner];
     }
 
-    function ownerOf(uint256 tokenId) public view returns (address) {
+    function ownerOf(uint256 tokenId) public override(IERC721) view returns (address) {
         address owner = _tokenOwner[tokenId];
         require(owner != address(0), "ERC721: owner query for nonexistent token");
 
         return owner;
     }
 
-    function approve(address to, uint256 tokenId) public {
+    function approve(address to, uint256 tokenId) public override(IERC721) {
         address owner = ownerOf(tokenId);
         require(to != owner, "ERC721: approval to current owner");
 
@@ -38,34 +38,34 @@ contract TestNFT is IERC165, IERC721 {
         emit Approval(owner, to, tokenId);
     }
 
-    function getApproved(uint256 tokenId) public view returns (address) {
+    function getApproved(uint256 tokenId) public override(IERC721) view returns (address) {
         require(_exists(tokenId), "ERC721: approved query for nonexistent token");
 
         return _tokenApprovals[tokenId];
     }
 
-    function setApprovalForAll(address to, bool approved) public {
+    function setApprovalForAll(address to, bool approved) public override(IERC721) {
         require(to != msg.sender, "ERC721: approve to caller");
 
         _operatorApprovals[msg.sender][to] = approved;
         emit ApprovalForAll(msg.sender, to, approved);
     }
 
-    function isApprovedForAll(address owner, address operator) public view returns (bool) {
+    function isApprovedForAll(address owner, address operator) public override(IERC721) view returns (bool) {
         return _operatorApprovals[owner][operator];
     }
 
-    function transferFrom(address from, address to, uint256 tokenId) public {
+    function transferFrom(address from, address to, uint256 tokenId) public override(IERC721) {
         require(_isApprovedOrOwner(msg.sender, tokenId), "ERC721: transfer caller is not owner nor approved");
 
         _transferFrom(from, to, tokenId);
     }
 
-    function safeTransferFrom(address from, address to, uint256 tokenId) public {
+    function safeTransferFrom(address from, address to, uint256 tokenId) public override(IERC721) {
         safeTransferFrom(from, to, tokenId, "");
     }
 
-    function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory _data) public {
+    function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory _data) public override(IERC721) {
         transferFrom(from, to, tokenId);
         require(_checkOnERC721Received(from, to, tokenId, _data), "ERC721: transfer to non ERC721Receiver implementer");
     }
@@ -131,7 +131,7 @@ contract TestNFT is IERC165, IERC721 {
         return size > 0;
     }
 
-    function supportsInterface(bytes4 interfaceID) external view returns (bool) {
+    function supportsInterface(bytes4 interfaceID) external override(IERC165) view returns (bool) {
         return interfaceID == _INTERFACE_ID_ERC721;
     }
 }
diff --git a/package.json b/scripts/package.json
similarity index 100%
rename from package.json
rename to scripts/package.json
diff --git a/yarn.lock b/scripts/yarn.lock
similarity index 100%
rename from yarn.lock
rename to scripts/yarn.lock