diff --git a/action/protocol/execution/evm/evmstatedbadapter_test.go b/action/protocol/execution/evm/evmstatedbadapter_test.go
index 1e5ed969d5..6d8a81eba4 100644
--- a/action/protocol/execution/evm/evmstatedbadapter_test.go
+++ b/action/protocol/execution/evm/evmstatedbadapter_test.go
@@ -9,6 +9,7 @@ import (
 	"bytes"
 	"context"
 	"math/big"
+	"strings"
 	"testing"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -947,19 +948,19 @@ func TestSortMap(t *testing.T) {
 		caches := []string{}
 		for i := 0; i < size; i++ {
 			stateDB.RevertToSnapshot(sn)
-			s := ""
+			var s strings.Builder
 			if stateDB.disableSortCachedContracts {
 				for _, c := range stateDB.cachedContract {
-					s += string(c.SelfState().Root[:])
+					s.WriteString(string(c.SelfState().Root[:]))
 				}
 			} else {
 				for _, addr := range stateDB.cachedContractAddrs() {
 					c := stateDB.cachedContract[addr]
-					s += string(c.SelfState().Root[:])
+					s.WriteString(string(c.SelfState().Root[:]))
 				}
 			}
 
-			caches = append(caches, s)
+			caches = append(caches, s.String())
 		}
 		return uniqueSlice(caches)
 	}
diff --git a/ioctl/client.go b/ioctl/client.go
index 91bd3206aa..645c3eacb2 100644
--- a/ioctl/client.go
+++ b/ioctl/client.go
@@ -440,10 +440,11 @@ func (c *client) Insecure() bool {
 }
 
 func (m *ConfirmationMessage) String() string {
-	line := fmt.Sprintf("%s\nOptions:", m.Info)
+	var line strings.Builder
+	line.WriteString(fmt.Sprintf("%s\nOptions:", m.Info))
 	for _, option := range m.Options {
-		line += " " + option
+		line.WriteString(" " + option)
 	}
-	line += "\nQuit for anything else."
-	return line
+	line.WriteString("\nQuit for anything else.")
+	return line.String()
 }
diff --git a/ioctl/cmd/action/actionhash.go b/ioctl/cmd/action/actionhash.go
index 50fc3cd607..5c3aa0badc 100644
--- a/ioctl/cmd/action/actionhash.go
+++ b/ioctl/cmd/action/actionhash.go
@@ -12,6 +12,7 @@ import (
 	"log"
 	"math/big"
 	"strconv"
+	"strings"
 
 	"github.com/grpc-ecosystem/go-grpc-middleware/util/metautils"
 	"github.com/iotexproject/go-pkgs/crypto"
@@ -167,20 +168,21 @@ func printActionProto(act *iotextypes.Action) (string, error) {
 	}
 	//ioctl action should display IOTX unit instead Raul
 	core := act.Core
-	result := fmt.Sprintf("\nversion: %d  ", core.GetVersion()) +
+	var result strings.Builder
+	result.WriteString(fmt.Sprintf("\nversion: %d  ", core.GetVersion()) +
 		fmt.Sprintf("txType: %d  ", core.GetTxType()) +
 		fmt.Sprintf("nonce: %d  ", core.GetNonce()) +
 		fmt.Sprintf("gasLimit: %d  ", core.GasLimit) +
 		fmt.Sprintf("chainID: %d  ", core.GetChainID()) +
 		fmt.Sprintf("encoding: %d\n", act.GetEncoding()) +
 		fmt.Sprintf("senderAddress: %s %s\n", senderAddress.String(),
-			Match(senderAddress.String(), "address"))
+			Match(senderAddress.String(), "address")))
 	if len(core.GasPrice) > 0 {
 		gasPriceUnitIOTX, err := util.StringToIOTX(core.GasPrice)
 		if err != nil {
 			return "", output.NewError(output.ConfigError, "failed to convert string to IOTX", err)
 		}
-		result += fmt.Sprintf("gasPrice: %s IOTX \n", gasPriceUnitIOTX)
+		result.WriteString(fmt.Sprintf("gasPrice: %s IOTX \n", gasPriceUnitIOTX))
 	}
 	if len(core.GetGasFeeCap()) > 0 {
 		feeCapIOTX, err := util.StringToIOTX(core.GetGasFeeCap())
@@ -191,28 +193,28 @@ func printActionProto(act *iotextypes.Action) (string, error) {
 		if err != nil {
 			return "", output.NewError(output.ConfigError, "failed to convert string to IOTX", err)
 		}
-		result += fmt.Sprintf("gasFeeCap: %s IOTX ", feeCapIOTX) +
-			fmt.Sprintf("gasTipCap: %s IOTX \n", tipCapIOTX)
+		result.WriteString(fmt.Sprintf("gasFeeCap: %s IOTX ", feeCapIOTX) +
+			fmt.Sprintf("gasTipCap: %s IOTX \n", tipCapIOTX))
 	}
 	if len(core.GetAccessList()) > 0 {
-		result += "accessList: <\n"
+		result.WriteString("accessList: <\n")
 		for _, access := range core.GetAccessList() {
-			result += fmt.Sprintf("  address: %s %s\n", access.Address,
-				Match(access.Address, "address"))
-			result += "  storageKeys: <\n"
+			result.WriteString(fmt.Sprintf("  address: %s %s\n", access.Address,
+				Match(access.Address, "address")))
+			result.WriteString("  storageKeys: <\n")
 			for _, key := range access.StorageKeys {
-				result += fmt.Sprintf("    %s\n", key)
+				result.WriteString(fmt.Sprintf("    %s\n", key))
 			}
-			result += "  >\n"
+			result.WriteString("  >\n")
 		}
-		result += ">\n"
+		result.WriteString(">\n")
 	}
 	if core.BlobTxData != nil {
-		result += fmt.Sprintf("blob hashes: <\n")
+		result.WriteString(fmt.Sprintf("blob hashes: <\n"))
 		for _, hash := range core.BlobTxData.BlobHashes {
-			result += fmt.Sprintf("  %x\n", hash)
+			result.WriteString(fmt.Sprintf("  %x\n", hash))
 		}
-		result += ">\n"
+		result.WriteString(">\n")
 	}
 
 	switch {
@@ -222,50 +224,50 @@ func printActionProto(act *iotextypes.Action) (string, error) {
 		if err != nil {
 			return "", output.NewError(output.ConvertError, "failed to convert string into IOTX amount", err)
 		}
-		result += "transfer: <\n" +
+		result.WriteString("transfer: <\n" +
 			fmt.Sprintf("  recipient: %s %s\n", transfer.Recipient,
 				Match(transfer.Recipient, "address")) +
-			fmt.Sprintf("  amount: %s IOTX\n", amount)
+			fmt.Sprintf("  amount: %s IOTX\n", amount))
 		if len(transfer.Payload) != 0 {
-			result += fmt.Sprintf("  payload: %s\n", transfer.Payload)
+			result.WriteString(fmt.Sprintf("  payload: %s\n", transfer.Payload))
 		}
-		result += ">\n"
+		result.WriteString(">\n")
 	case core.GetExecution() != nil:
 		execution := core.GetExecution()
-		result += "execution: <\n" +
+		result.WriteString("execution: <\n" +
 			fmt.Sprintf("  contract: %s %s\n", execution.Contract,
-				Match(execution.Contract, "address"))
+				Match(execution.Contract, "address")))
 		if execution.Amount != "0" {
 			amount, err := util.StringToIOTX(execution.Amount)
 			if err != nil {
 				return "", output.NewError(output.ConvertError, "failed to convert string into IOTX amount", err)
 			}
-			result += fmt.Sprintf("  amount: %s IOTX\n", amount)
+			result.WriteString(fmt.Sprintf("  amount: %s IOTX\n", amount))
 		}
-		result += fmt.Sprintf("  data: %x\n", execution.Data) + ">\n"
+		result.WriteString(fmt.Sprintf("  data: %x\n", execution.Data) + ">\n")
 	case core.GetPutPollResult() != nil:
 		putPollResult := core.GetPutPollResult()
-		result += "putPollResult: <\n" +
+		result.WriteString("putPollResult: <\n" +
 			fmt.Sprintf("  height: %d\n", putPollResult.Height) +
-			"  candidates: <\n"
+			"  candidates: <\n")
 		for _, candidate := range putPollResult.Candidates.Candidates {
-			result += "    candidate: <\n" +
-				fmt.Sprintf("      address: %s\n", candidate.Address)
+			result.WriteString("    candidate: <\n" +
+				fmt.Sprintf("      address: %s\n", candidate.Address))
 			votes := big.NewInt(0).SetBytes(candidate.Votes)
-			result += fmt.Sprintf("      votes: %s\n", votes.String()) +
+			result.WriteString(fmt.Sprintf("      votes: %s\n", votes.String()) +
 				fmt.Sprintf("      rewardAdress: %s\n", candidate.RewardAddress) +
-				"    >\n"
+				"    >\n")
 		}
-		result += "  >\n" +
-			">\n"
+		result.WriteString("  >\n" +
+			">\n")
 	default:
 		bs, _ := protoV1.Marshal(core)
-		result += string(bs)
+		result.WriteString(string(bs))
 	}
-	result += fmt.Sprintf("senderPubKey: %x\n", act.SenderPubKey) +
-		fmt.Sprintf("signature: %x\n", act.Signature)
+	result.WriteString(fmt.Sprintf("senderPubKey: %x\n", act.SenderPubKey) +
+		fmt.Sprintf("signature: %x\n", act.Signature))
 
-	return result, nil
+	return result.String(), nil
 }
 
 func printReceiptProto(receipt *iotextypes.Receipt) string {
@@ -310,23 +312,24 @@ func printReceiptProto(receipt *iotextypes.Receipt) string {
 }
 
 func printLogs(logs []*iotextypes.Log) string {
-	result := "logs:<\n"
+	var result strings.Builder
+	result.WriteString("logs:<\n")
 	for _, l := range logs {
-		result += "  <\n" +
+		result.WriteString("  <\n" +
 			fmt.Sprintf("    contractAddress: %s\n", l.ContractAddress) +
-			"    topics:<\n"
+			"    topics:<\n")
 		for _, topic := range l.Topics {
-			result += fmt.Sprintf("      %s\n", hex.EncodeToString(topic))
+			result.WriteString(fmt.Sprintf("      %s\n", hex.EncodeToString(topic)))
 		}
-		result += "    >\n"
+		result.WriteString("    >\n")
 		if len(l.Data) > 0 {
-			result += fmt.Sprintf("    data: %s\n", hex.EncodeToString(l.Data))
+			result.WriteString(fmt.Sprintf("    data: %s\n", hex.EncodeToString(l.Data)))
 		}
-		result += "  >\n"
+		result.WriteString("  >\n")
 
 	}
-	result += ">\n"
-	return result
+	result.WriteString(">\n")
+	return result.String()
 }
 
 // Match returns human readable expression
diff --git a/ioctl/cmd/alias/aliasimport.go b/ioctl/cmd/alias/aliasimport.go
index 8805672da6..0f7c055577 100644
--- a/ioctl/cmd/alias/aliasimport.go
+++ b/ioctl/cmd/alias/aliasimport.go
@@ -9,6 +9,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"strings"
 
 	"github.com/spf13/cobra"
 	yaml "gopkg.in/yaml.v2"
@@ -106,11 +107,12 @@ func aliasImport(cmd *cobra.Command, args []string) error {
 
 func (m *importMessage) String() string {
 	if output.Format == "" {
-		line := fmt.Sprintf("%d/%d aliases imported\nExisted aliases:", m.ImportedNumber, m.TotalNumber)
+		var line strings.Builder
+		line.WriteString(fmt.Sprintf("%d/%d aliases imported\nExisted aliases:", m.ImportedNumber, m.TotalNumber))
 		for _, alias := range m.Unimported {
-			line += fmt.Sprint(" " + alias.Name)
+			line.WriteString(fmt.Sprint(" " + alias.Name))
 		}
-		return line
+		return line.String()
 	}
 	return output.FormatString(output.Result, m)
 }
diff --git a/ioctl/newcmd/action/actionhash.go b/ioctl/newcmd/action/actionhash.go
index 7db289dd26..d129e2431b 100644
--- a/ioctl/newcmd/action/actionhash.go
+++ b/ioctl/newcmd/action/actionhash.go
@@ -12,6 +12,7 @@ import (
 	"log"
 	"math/big"
 	"strconv"
+	"strings"
 
 	"github.com/grpc-ecosystem/go-grpc-middleware/util/metautils"
 	"github.com/iotexproject/go-pkgs/crypto"
@@ -169,14 +170,15 @@ func printActionProto(client ioctl.Client, action *iotextypes.Action) (string, e
 	if err != nil {
 		return "", errors.Wrap(err, "failed to convert string to IOTX")
 	}
-	result := fmt.Sprintf("\nversion: %d  ", core.GetVersion()) +
+	var result strings.Builder
+	result.WriteString(fmt.Sprintf("\nversion: %d  ", core.GetVersion()) +
 		fmt.Sprintf("nonce: %d  ", core.GetNonce()) +
 		fmt.Sprintf("gasLimit: %d  ", core.GasLimit) +
 		fmt.Sprintf("gasPrice: %s IOTX  ", gasPriceUnitIOTX) +
 		fmt.Sprintf("chainID: %d  ", core.GetChainID()) +
 		fmt.Sprintf("encoding: %d\n", action.GetEncoding()) +
 		fmt.Sprintf("senderAddress: %s %s\n", senderAddress.String(),
-			Match(client, senderAddress.String(), "address"))
+			Match(client, senderAddress.String(), "address")))
 	switch {
 	case core.GetTransfer() != nil:
 		transfer := core.GetTransfer()
@@ -184,53 +186,53 @@ func printActionProto(client ioctl.Client, action *iotextypes.Action) (string, e
 		if err != nil {
 			return "", errors.Wrap(err, "failed to convert string into IOTX amount")
 		}
-		result += "transfer: <\n" +
+		result.WriteString("transfer: <\n" +
 			fmt.Sprintf("  recipient: %s %s\n", transfer.Recipient,
 				Match(client, transfer.Recipient, "address")) +
-			fmt.Sprintf("  amount: %s IOTX\n", amount)
+			fmt.Sprintf("  amount: %s IOTX\n", amount))
 		if len(transfer.Payload) != 0 {
-			result += fmt.Sprintf("  payload: %s\n", transfer.Payload)
+			result.WriteString(fmt.Sprintf("  payload: %s\n", transfer.Payload))
 		}
-		result += ">\n"
+		result.WriteString(">\n")
 	case core.GetExecution() != nil:
 		execution := core.GetExecution()
-		result += "execution: <\n" +
+		result.WriteString("execution: <\n" +
 			fmt.Sprintf("  contract: %s %s\n", execution.Contract,
-				Match(client, execution.Contract, "address"))
+				Match(client, execution.Contract, "address")))
 		if execution.Amount != "0" {
 			amount, err := util.StringToIOTX(execution.Amount)
 			if err != nil {
 				return "", errors.Wrap(err, "failed to convert string into IOTX amount")
 			}
-			result += fmt.Sprintf("  amount: %s IOTX\n", amount)
+			result.WriteString(fmt.Sprintf("  amount: %s IOTX\n", amount))
 		}
-		result += fmt.Sprintf("  data: %x\n", execution.Data) + ">\n"
+		result.WriteString(fmt.Sprintf("  data: %x\n", execution.Data) + ">\n")
 	case core.GetPutPollResult() != nil:
 		putPollResult := core.GetPutPollResult()
-		result += "putPollResult: <\n" +
+		result.WriteString("putPollResult: <\n" +
 			fmt.Sprintf("  height: %d\n", putPollResult.Height) +
-			"  candidates: <\n"
+			"  candidates: <\n")
 		for _, candidate := range putPollResult.Candidates.Candidates {
-			result += "    candidate: <\n" +
-				fmt.Sprintf("      address: %s\n", candidate.Address)
+			result.WriteString("    candidate: <\n" +
+				fmt.Sprintf("      address: %s\n", candidate.Address))
 			votes := big.NewInt(0).SetBytes(candidate.Votes)
-			result += fmt.Sprintf("      votes: %s\n", votes.String()) +
+			result.WriteString(fmt.Sprintf("      votes: %s\n", votes.String()) +
 				fmt.Sprintf("      rewardAdress: %s\n", candidate.RewardAddress) +
-				"    >\n"
+				"    >\n")
 		}
-		result += "  >\n" +
-			">\n"
+		result.WriteString("  >\n" +
+			">\n")
 	default:
 		bs, err := protoV1.Marshal(core)
 		if err != nil {
 			return "", errors.Wrap(err, "failed to marshal core")
 		}
-		result += string(bs)
+		result.WriteString(string(bs))
 	}
-	result += fmt.Sprintf("senderPubKey: %x\n", action.SenderPubKey) +
-		fmt.Sprintf("signature: %x\n", action.Signature)
+	result.WriteString(fmt.Sprintf("senderPubKey: %x\n", action.SenderPubKey) +
+		fmt.Sprintf("signature: %x\n", action.Signature))
 
-	return result, nil
+	return result.String(), nil
 }
 
 func printReceiptProto(client ioctl.Client, receipt *iotextypes.Receipt) string {
@@ -256,23 +258,24 @@ func printReceiptProto(client ioctl.Client, receipt *iotextypes.Receipt) string
 }
 
 func printLogs(logs []*iotextypes.Log) string {
-	result := "logs:<\n"
+	var result strings.Builder
+	result.WriteString("logs:<\n")
 	for _, l := range logs {
-		result += "  <\n" +
+		result.WriteString("  <\n" +
 			fmt.Sprintf("    contractAddress: %s\n", l.ContractAddress) +
-			"    topics:<\n"
+			"    topics:<\n")
 		for _, topic := range l.Topics {
-			result += fmt.Sprintf("      %s\n", hex.EncodeToString(topic))
+			result.WriteString(fmt.Sprintf("      %s\n", hex.EncodeToString(topic)))
 		}
-		result += "    >\n"
+		result.WriteString("    >\n")
 		if len(l.Data) > 0 {
-			result += fmt.Sprintf("    data: %s\n", hex.EncodeToString(l.Data))
+			result.WriteString(fmt.Sprintf("    data: %s\n", hex.EncodeToString(l.Data)))
 		}
-		result += "  >\n"
+		result.WriteString("  >\n")
 
 	}
-	result += ">\n"
-	return result
+	result.WriteString(">\n")
+	return result.String()
 }
 
 // Match returns human readable expression
diff --git a/ioctl/newcmd/alias/aliasimport.go b/ioctl/newcmd/alias/aliasimport.go
index 504a9f4a27..9cb629c4a5 100644
--- a/ioctl/newcmd/alias/aliasimport.go
+++ b/ioctl/newcmd/alias/aliasimport.go
@@ -8,6 +8,7 @@ package alias
 import (
 	"encoding/json"
 	"fmt"
+	"strings"
 
 	"github.com/pkg/errors"
 	"github.com/spf13/cobra"
@@ -96,11 +97,12 @@ func NewAliasImport(c ioctl.Client) *cobra.Command {
 				return errors.Wrapf(err, failToWriteToConfigFile)
 			}
 
-			line := fmt.Sprintf("%d/%d aliases imported\nExisted aliases:", message.ImportedNumber, message.TotalNumber)
+			var line strings.Builder
+			line.WriteString(fmt.Sprintf("%d/%d aliases imported\nExisted aliases:", message.ImportedNumber, message.TotalNumber))
 			for _, alias := range message.Unimported {
-				line += fmt.Sprint(" " + alias.Name)
+				line.WriteString(fmt.Sprint(" " + alias.Name))
 			}
-			cmd.Println(line)
+			cmd.Println(line.String())
 			return nil
 		},
 	}
diff --git a/ioctl/output/format.go b/ioctl/output/format.go
index 9244518af5..1281f5198c 100644
--- a/ioctl/output/format.go
+++ b/ioctl/output/format.go
@@ -9,6 +9,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"log"
+	"strings"
 )
 
 // Format is the target of output-format flag
@@ -97,12 +98,13 @@ type ConfirmationMessage struct {
 
 func (m *ConfirmationMessage) String() string {
 	if Format == "" {
-		line := fmt.Sprintf("%s\nOptions:", m.Info)
+		var line strings.Builder
+		line.WriteString(fmt.Sprintf("%s\nOptions:", m.Info))
 		for _, option := range m.Options {
-			line += " " + option
+			line.WriteString(" " + option)
 		}
-		line += "\nQuit for anything else."
-		return line
+		line.WriteString("\nQuit for anything else.")
+		return line.String()
 	}
 	return FormatString(Confirmation, m)
 }
diff --git a/tools/bot/server/bot/execution.go b/tools/bot/server/bot/execution.go
index 3e8988ae78..8d62748427 100644
--- a/tools/bot/server/bot/execution.go
+++ b/tools/bot/server/bot/execution.go
@@ -117,36 +117,37 @@ func (s *Execution) exec(pri crypto.PrivateKey) (txhash string, err error) {
 		err = errors.New("address len is not equal to amount len")
 		return
 	}
-	data := _multiSendSha3 + _multiSendOffset
+	var data strings.Builder
+	data.WriteString(_multiSendSha3 + _multiSendOffset)
 	params2Offset := 32*3 + 1*32 + len(s.cfg.Execution.To.Address)*32
 	params := fmt.Sprintf("%x", params2Offset)
-	data += strings.Repeat("0", 64-len(params)) + params
+	data.WriteString(strings.Repeat("0", 64-len(params)) + params)
 
 	params3Offset := params2Offset + 1*32 + len(s.cfg.Execution.To.Address)*32
 	params = fmt.Sprintf("%x", params3Offset)
-	data += strings.Repeat("0", 64-len(params)) + params
+	data.WriteString(strings.Repeat("0", 64-len(params)) + params)
 
 	lenOfAddress := fmt.Sprintf("%x", len(s.cfg.Execution.To.Address))
-	data += strings.Repeat("0", 64-len(lenOfAddress)) + lenOfAddress
+	data.WriteString(strings.Repeat("0", 64-len(lenOfAddress)) + lenOfAddress)
 	for _, addr := range s.cfg.Execution.To.Address {
 		a, errs := address.FromString(addr)
 		if errs != nil {
 			err = errs
 			return
 		}
-		data += _prefixZero + hex.EncodeToString(a.Bytes())
+		data.WriteString(_prefixZero + hex.EncodeToString(a.Bytes()))
 	}
-	data += strings.Repeat("0", 64-len(lenOfAddress)) + lenOfAddress
+	data.WriteString(strings.Repeat("0", 64-len(lenOfAddress)) + lenOfAddress)
 	for _, amount := range s.cfg.Execution.To.Amount {
 		amo, ok := new(big.Int).SetString(amount, 10)
 		if !ok {
 			err = errors.New("amount convert error")
 			return
 		}
-		data += strings.Repeat("0", 64-len(amo.Text(16))) + amo.Text(16)
+		data.WriteString(strings.Repeat("0", 64-len(amo.Text(16))) + amo.Text(16))
 	}
-	data += _fixPayLoad
-	dataBytes, err := hex.DecodeString(data)
+	data.WriteString(_fixPayLoad)
+	dataBytes, err := hex.DecodeString(data.String())
 	if err != nil {
 		return
 	}