diff --git a/ethers/basics.nim b/ethers/basics.nim
index 2896a96..76662e1 100644
--- a/ethers/basics.nim
+++ b/ethers/basics.nim
@@ -11,3 +11,6 @@ export results
 export stint
 export upraises
 export address
+
+type
+  EthersError* = object of IOError
diff --git a/ethers/contract.nim b/ethers/contract.nim
index ee2c5f4..7e79f5c 100644
--- a/ethers/contract.nim
+++ b/ethers/contract.nim
@@ -11,7 +11,7 @@ type
   Contract* = ref object of RootObj
     provider: Provider
     address: Address
-  ContractError* = object of IOError
+  ContractError* = object of EthersError
 
 template raiseContractError(message: string) =
   raise newException(ContractError, message)
diff --git a/ethers/providers/jsonrpc.nim b/ethers/providers/jsonrpc.nim
index 0562cc7..19412d8 100644
--- a/ethers/providers/jsonrpc.nim
+++ b/ethers/providers/jsonrpc.nim
@@ -16,7 +16,7 @@ type
   JsonRpcSigner* = ref object of Signer
     provider: JsonRpcProvider
     address: ?Address
-  JsonRpcProviderError* = object of IOError
+  JsonRpcProviderError* = object of EthersError
 
 template raiseProviderError(message: string) =
   raise newException(JsonRpcProviderError, message)
diff --git a/ethers/providers/rpccalls/conversions.nim b/ethers/providers/rpccalls/conversions.nim
index 1066560..1a21ed7 100644
--- a/ethers/providers/rpccalls/conversions.nim
+++ b/ethers/providers/rpccalls/conversions.nim
@@ -26,17 +26,25 @@ func fromJson*(json: JsonNode, name: string, result: var Address) =
 # UInt256
 
 func `%`*(integer: UInt256): JsonNode =
-  %toHex(integer)
+  %("0x" & toHex(integer))
 
 func fromJson*(json: JsonNode, name: string, result: var UInt256) =
   result = UInt256.fromHex(json.getStr())
 
 # Transaction
 
-func `%`*(tx: Transaction): JsonNode =
-  result = %{ "to": %tx.to, "data": %tx.data }
-  if sender =? tx.sender:
+func `%`*(transaction: Transaction): JsonNode =
+  result = %{ "to": %transaction.to, "data": %transaction.data }
+  if sender =? transaction.sender:
     result["from"] = %sender
+  if nonce =? transaction.nonce:
+    result["nonce"] = %nonce
+  if chainId =? transaction.chainId:
+    result["chainId"] = %chainId
+  if gasPrice =? transaction.gasPrice:
+    result["gasPrice"] = %gasPrice
+  if gasLimit =? transaction.gasLimit:
+    result["gas"] = %gasLimit
 
 # BlockTag
 
diff --git a/ethers/signer.nim b/ethers/signer.nim
index b1c4bf7..200db89 100644
--- a/ethers/signer.nim
+++ b/ethers/signer.nim
@@ -4,6 +4,10 @@ import ./provider
 export basics
 
 type Signer* = ref object of RootObj
+type SignerError* = object of EthersError
+
+template raiseSignerError(message: string) =
+  raise newException(SignerError, message)
 
 method provider*(signer: Signer): Provider {.base.} =
   doAssert false, "not implemented"
@@ -28,3 +32,27 @@ method estimateGas*(signer: Signer,
 
 method getChainId*(signer: Signer): Future[UInt256] {.base.} =
   signer.provider.getChainId()
+
+method populateTransaction*(signer: Signer,
+                            transaction: Transaction):
+                           Future[Transaction] {.base, async.} =
+
+  if sender =? transaction.sender and sender != await signer.getAddress():
+    raiseSignerError("from address mismatch")
+  if chainId =? transaction.chainId and chainId != await signer.getChainId():
+    raiseSignerError("chain id mismatch")
+
+  var populated = transaction
+
+  if transaction.sender.isNone:
+    populated.sender = some(await signer.getAddress())
+  if transaction.nonce.isNone:
+    populated.nonce = some(await signer.getTransactionCount(BlockTag.pending))
+  if transaction.chainId.isNone:
+    populated.chainId = some(await signer.getChainId())
+  if transaction.gasPrice.isNone:
+    populated.gasPrice = some(await signer.getGasPrice())
+  if transaction.gasLimit.isNone:
+    populated.gasLimit = some(await signer.estimateGas(populated))
+
+  return populated
diff --git a/ethers/transaction.nim b/ethers/transaction.nim
index 7ec828b..c80a54b 100644
--- a/ethers/transaction.nim
+++ b/ethers/transaction.nim
@@ -5,6 +5,10 @@ type Transaction* = object
   sender*: ?Address
   to*: Address
   data*: seq[byte]
+  nonce*: ?UInt256
+  chainId*: ?UInt256
+  gasPrice*: ?UInt256
+  gasLimit*: ?UInt256
 
 func `$`*(transaction: Transaction): string =
   result = "("
@@ -12,4 +16,12 @@ func `$`*(transaction: Transaction): string =
     result &= "from: " & $sender & ", "
   result &= "to: " & $transaction.to & ", "
   result &= "data: 0x" & $transaction.data.toHex
+  if nonce =? transaction.nonce:
+    result &= ", nonce: 0x" & $nonce.toHex
+  if chainId =? transaction.chainId:
+    result &= ", chainId: " & $chainId
+  if gasPrice =? transaction.gasPrice:
+    result &= ", gasPrice: 0x" & $gasPrice.toHex
+  if gasLimit =? transaction.gasLimit:
+    result &= ", gasLimit: 0x" & $gasLimit.toHex
   result &= ")"
diff --git a/testmodule/examples.nim b/testmodule/examples.nim
index b4eba00..dfd7345 100644
--- a/testmodule/examples.nim
+++ b/testmodule/examples.nim
@@ -4,15 +4,21 @@ import pkg/ethers
 
 randomize()
 
-proc example*(_: type Address): Address =
-  var address: array[20, byte]
-  for b in address.mitems:
+proc example*[N](_: type array[N, byte]): array[N, byte] =
+  var a: array[N, byte]
+  for b in a.mitems:
     b = rand(byte)
-  Address.init(address)
+  a
 
 proc example*(_: type seq[byte]): seq[byte] =
   let length = rand(0..<20)
   newSeqWith(length, rand(byte))
 
+proc example*(_: type Address): Address =
+  Address.init(array[20, byte].example)
+
+proc example*(_: type UInt256): UInt256 =
+  UInt256.fromBytesBE(array[32, byte].example)
+
 proc example*(_: type Transaction): Transaction =
   Transaction(to: Address.example, data: seq[byte].example)
diff --git a/testmodule/testJsonRpcSigner.nim b/testmodule/testJsonRpcSigner.nim
index 1b8a1dd..d424b71 100644
--- a/testmodule/testJsonRpcSigner.nim
+++ b/testmodule/testJsonRpcSigner.nim
@@ -38,3 +38,38 @@ suite "JsonRpcSigner":
     let signer = provider.getSigner()
     let chainId = await signer.getChainId()
     check chainId == 31337.u256 # hardhat chain id
+
+  test "can populate missing fields in a transaction":
+    let signer = provider.getSigner()
+    let transaction = Transaction.example
+    let populated = await signer.populateTransaction(transaction)
+    check !populated.sender == await signer.getAddress()
+    check !populated.gasPrice == await signer.getGasPrice()
+    check !populated.nonce == await signer.getTransactionCount(BlockTag.pending)
+    check !populated.gasLimit == await signer.estimateGas(transaction)
+    check !populated.chainId == await signer.getChainId()
+
+  test "populate does not overwrite existing fields":
+    let signer = provider.getSigner()
+    var transaction = Transaction.example
+    transaction.sender = some await signer.getAddress()
+    transaction.nonce = some UInt256.example
+    transaction.chainId = some await signer.getChainId()
+    transaction.gasPrice = some UInt256.example
+    transaction.gasLimit = some UInt256.example
+    let populated = await signer.populateTransaction(transaction)
+    check populated == transaction
+
+  test "populate fails when sender does not match signer address":
+    let signer = provider.getSigner()
+    var transaction = Transaction.example
+    transaction.sender = accounts[1].some
+    expect SignerError:
+      discard await signer.populateTransaction(transaction)
+
+  test "populate fails when chain id does not match":
+    let signer = provider.getSigner()
+    var transaction = Transaction.example
+    transaction.chainId = 0xdeadbeef.u256.some
+    expect SignerError:
+      discard await signer.populateTransaction(transaction)