diff --git a/.github/workflows/go.yml b/.github/workflows/go.yml
index 6fdc7701..73b22a88 100644
--- a/.github/workflows/go.yml
+++ b/.github/workflows/go.yml
@@ -43,7 +43,7 @@ jobs:
       run: go run ./script/run-test --reset-instrument --debug -v -cover -coverpkg github.com/xhd2015/xgo/runtime/... -coverprofile cover.out
 
     - name: Merge Coverages
-      run: go run ./script/cover merge ./cover-runtime.out ./cover-runtime-sub.out -o cover-runtime-merged.out
+      run: go run ./cmd/coverage merge ./cover-runtime.out ./cover-runtime-sub.out -o cover-runtime-merged.out --exclude-prefix github.com/xhd2015/xgo/runtime/test
 
     - name: Print coverage
       run: cd runtime && go tool cover --func ../cover-runtime-merged.out
diff --git a/cmd/coverage/main.go b/cmd/coverage/main.go
new file mode 100644
index 00000000..56823055
--- /dev/null
+++ b/cmd/coverage/main.go
@@ -0,0 +1,14 @@
+package main
+
+import (
+	"os"
+
+	"github.com/xhd2015/xgo/cmd/xgo/coverage"
+)
+
+func main() {
+	// os.Arg[0] = coverage
+	// os.Arg[1] = args
+	args := os.Args[1:]
+	coverage.Main(args)
+}
diff --git a/cmd/xgo/coverage/help.go b/cmd/xgo/coverage/help.go
new file mode 100644
index 00000000..6826f76c
--- /dev/null
+++ b/cmd/xgo/coverage/help.go
@@ -0,0 +1,22 @@
+package coverage
+
+const help = `
+Xgo tool coverage is a tool to view and merge go coverage profiles, just like an extension to go tool cover.
+
+Usage:
+    xgo tool coverage <cmd> [arguments]
+
+The commands are:
+    merge       merge coverage profiles
+    help        show help message
+
+Options for merge:
+    -o <file>               output to file instead of stdout
+    --exclude-prefix <pkg>  exclude coverage of a specific package and sub packages
+
+Examples:
+    xgo tool coverage merge -o cover.a cover-a.out cover-b.out     merge multiple files into one
+
+See https://github.com/xhd2015/xgo for documentation.
+
+`
diff --git a/cmd/xgo/coverage/main.go b/cmd/xgo/coverage/main.go
new file mode 100644
index 00000000..acff2a55
--- /dev/null
+++ b/cmd/xgo/coverage/main.go
@@ -0,0 +1,135 @@
+package coverage
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"strings"
+
+	"github.com/xhd2015/xgo/support/coverage"
+)
+
+func Main(args []string) {
+	if len(args) == 0 {
+		fmt.Fprintf(os.Stderr, "requires cmd\n")
+		os.Exit(1)
+	}
+	cmd := args[0]
+	if cmd == "help" {
+		fmt.Print(strings.TrimPrefix(help, "\n"))
+		return
+	}
+	args = args[1:]
+
+	var remainArgs []string
+	var outFile string
+	n := len(args)
+
+	var flagHelp bool
+	var excludePrefix []string
+	for i := 0; i < n; i++ {
+		arg := args[i]
+		if arg == "--" {
+			remainArgs = append(remainArgs, args[i+1:]...)
+			break
+		}
+		if arg == "-o" {
+			if i+1 >= n {
+				fmt.Fprintf(os.Stderr, "%s requires file\n", arg)
+				os.Exit(1)
+			}
+			outFile = args[i+1]
+			i++
+			continue
+		}
+		if arg == "--exclude-prefix" {
+			if i+1 >= n {
+				fmt.Fprintf(os.Stderr, "%s requires argument\n", arg)
+				os.Exit(1)
+			}
+			if args[i+1] == "" {
+				fmt.Fprintf(os.Stderr, "%s requires non empty argument\n", arg)
+				os.Exit(1)
+			}
+			excludePrefix = append(excludePrefix, args[i+1])
+			i++
+			continue
+		}
+		if arg == "--help" || arg == "-h" {
+			flagHelp = true
+			continue
+		}
+		if !strings.HasPrefix(arg, "-") {
+			remainArgs = append(remainArgs, arg)
+			continue
+		}
+		fmt.Fprintf(os.Stderr, "unrecognized flag: %s\n", arg)
+		os.Exit(1)
+	}
+	if flagHelp {
+		fmt.Print(strings.TrimPrefix(help, "\n"))
+		return
+	}
+
+	switch cmd {
+	case "merge":
+		if len(remainArgs) == 0 {
+			fmt.Fprintf(os.Stderr, "requires files\n")
+			os.Exit(1)
+		}
+		err := mergeCover(remainArgs, outFile, excludePrefix)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "%v\n", err)
+			os.Exit(1)
+		}
+	default:
+		fmt.Fprintf(os.Stderr, "unrecognized cmd: %s\n", cmd)
+		os.Exit(1)
+	}
+}
+
+func mergeCover(files []string, outFile string, excludePrefix []string) error {
+	var mode string
+	covs := make([][]*coverage.CovLine, 0, len(files))
+	for _, file := range files {
+		content, err := os.ReadFile(file)
+		if err != nil {
+			return err
+		}
+		covMode, cov := coverage.Parse(string(content))
+		covs = append(covs, cov)
+		if mode == "" {
+			mode = covMode
+		}
+	}
+	res := coverage.Merge(covs...)
+	res = coverage.Filter(res, func(line *coverage.CovLine) bool {
+		return !hasAnyPrefix(line.Prefix, excludePrefix)
+	})
+
+	if mode == "" {
+		mode = "set"
+	}
+	mergedCov := coverage.Format(mode, res)
+
+	var out io.Writer = os.Stdout
+	if outFile != "" {
+		file, err := os.Create(outFile)
+		if err != nil {
+			return err
+		}
+		defer file.Close()
+		out = file
+	}
+	_, err := io.WriteString(out, mergedCov)
+	return err
+}
+
+func hasAnyPrefix(s string, prefixes []string) bool {
+	for _, prefix := range prefixes {
+		if strings.HasPrefix(s, prefix) {
+			return true
+		}
+	}
+	return false
+}
diff --git a/cmd/xgo/runtime_gen/core/version.go b/cmd/xgo/runtime_gen/core/version.go
index b9ae3d7d..17938bbf 100755
--- a/cmd/xgo/runtime_gen/core/version.go
+++ b/cmd/xgo/runtime_gen/core/version.go
@@ -6,9 +6,9 @@ import (
 	"os"
 )
 
-const VERSION = "1.0.30"
-const REVISION = "83fdf348a92806bbdc0b6746fc7d55ae1671dfab+1"
-const NUMBER = 209
+const VERSION = "1.0.31"
+const REVISION = "12ae038b4e052f42cd97af0721488c1b5f77eb6e+1"
+const NUMBER = 210
 
 // these fields will be filled by compiler
 const XGO_VERSION = ""
diff --git a/cmd/xgo/tool.go b/cmd/xgo/tool.go
index 776701c7..06671a44 100644
--- a/cmd/xgo/tool.go
+++ b/cmd/xgo/tool.go
@@ -8,13 +8,19 @@ import (
 	"runtime"
 	"strings"
 
+	"github.com/xhd2015/xgo/cmd/xgo/coverage"
 	"github.com/xhd2015/xgo/cmd/xgo/trace"
 	"github.com/xhd2015/xgo/support/cmd"
 )
 
 func handleTool(tool string, args []string) error {
 	if tool == "trace" {
-		return trace.Main(args)
+		trace.Main(args)
+		return nil
+	}
+	if tool == "coverage" {
+		coverage.Main(args)
+		return nil
 	}
 	tools := []string{
 		tool,
diff --git a/cmd/xgo/trace/main.go b/cmd/xgo/trace/main.go
index 1dfbaf48..f50e79b2 100644
--- a/cmd/xgo/trace/main.go
+++ b/cmd/xgo/trace/main.go
@@ -20,13 +20,13 @@ import (
 	"github.com/xhd2015/xgo/support/cmd"
 )
 
-func Main(args []string) error {
+func Main(args []string) {
 	if len(args) == 0 {
-		return errors.New("requires file")
+		fmt.Fprintf(os.Stderr, "requires file\n")
+		os.Exit(1)
 	}
 	file := args[0]
 	serveFile(file)
-	return nil
 }
 
 func serveFile(file string) {
diff --git a/cmd/xgo/version.go b/cmd/xgo/version.go
index 542c738a..c967cbc4 100644
--- a/cmd/xgo/version.go
+++ b/cmd/xgo/version.go
@@ -2,9 +2,9 @@ package main
 
 import "fmt"
 
-const VERSION = "1.0.30"
-const REVISION = "83fdf348a92806bbdc0b6746fc7d55ae1671dfab+1"
-const NUMBER = 209
+const VERSION = "1.0.31"
+const REVISION = "12ae038b4e052f42cd97af0721488c1b5f77eb6e+1"
+const NUMBER = 210
 
 func getRevision() string {
 	revSuffix := ""
diff --git a/runtime/core/version.go b/runtime/core/version.go
index b9ae3d7d..17938bbf 100644
--- a/runtime/core/version.go
+++ b/runtime/core/version.go
@@ -6,9 +6,9 @@ import (
 	"os"
 )
 
-const VERSION = "1.0.30"
-const REVISION = "83fdf348a92806bbdc0b6746fc7d55ae1671dfab+1"
-const NUMBER = 209
+const VERSION = "1.0.31"
+const REVISION = "12ae038b4e052f42cd97af0721488c1b5f77eb6e+1"
+const NUMBER = 210
 
 // these fields will be filled by compiler
 const XGO_VERSION = ""
diff --git a/script/cover/cover.go b/script/cover/cover.go
index a9e7a1f6..7bf7fe18 100644
--- a/script/cover/cover.go
+++ b/script/cover/cover.go
@@ -4,8 +4,9 @@ import (
 	"fmt"
 	"io"
 	"os"
-	"strconv"
 	"strings"
+
+	"github.com/xhd2015/xgo/support/coverage"
 )
 
 func main() {
@@ -54,23 +55,23 @@ func main() {
 }
 
 func mergeCover(files []string, outFile string) error {
-	covs := make([][]*covLine, 0, len(files))
+	covs := make([][]*coverage.CovLine, 0, len(files))
 	for _, file := range files {
 		content, err := os.ReadFile(file)
 		if err != nil {
 			return err
 		}
-		covs = append(covs, parseCover(string(content)))
+		covs = append(covs, coverage.Parse(string(content)))
 	}
-	res := merge(covs)
-	res = filter(res, func(line *covLine) bool {
-		if strings.HasPrefix(line.prefix, "github.com/xhd2015/xgo/runtime/test") {
+	res := coverage.Merge(covs...)
+	res = coverage.Filter(res, func(line *coverage.CovLine) bool {
+		if strings.HasPrefix(line.Prefix, "github.com/xhd2015/xgo/runtime/test") {
 			return false
 		}
 		return true
 	})
 
-	mergedCov := formatCoverage("set", res)
+	mergedCov := coverage.Format("set", res)
 
 	var out io.Writer = os.Stdout
 	if outFile != "" {
@@ -84,93 +85,3 @@ func mergeCover(files []string, outFile string) error {
 	_, err := io.WriteString(out, mergedCov)
 	return err
 }
-
-func filter(covs []*covLine, check func(line *covLine) bool) []*covLine {
-	n := len(covs)
-	j := 0
-	for i := 0; i < n; i++ {
-		if check(covs[i]) {
-			covs[j] = covs[i]
-			j++
-		}
-	}
-	return covs[:j]
-}
-
-func formatCoverage(mode string, lines []*covLine) string {
-	strs := make([]string, 0, len(lines)+1)
-	strs = append(strs, "mode: "+mode)
-	for _, line := range lines {
-		strs = append(strs, line.prefix+" "+strconv.FormatInt(line.count, 10))
-	}
-	return strings.Join(strs, "\n")
-}
-
-func merge(covs [][]*covLine) []*covLine {
-	if len(covs) == 0 {
-		return nil
-	}
-	if len(covs) == 1 {
-		return covs[0]
-	}
-	result := covs[0]
-	for i := 1; i < len(covs); i++ {
-		result = mergeCov(result, covs[i])
-	}
-	return result
-}
-
-func mergeCov(a []*covLine, b []*covLine) []*covLine {
-	for _, line := range b {
-		idx := -1
-		for i := 0; i < len(a); i++ {
-			if a[i].prefix == line.prefix {
-				idx = i
-				break
-			}
-		}
-		if idx < 0 {
-			a = append(a, line)
-		} else {
-			// fmt.Printf("add %s %d %d\n", a[idx].prefix, a[idx].count, line.count)
-			a[idx].count += line.count
-		}
-	}
-	return a
-}
-
-type covLine struct {
-	prefix string
-	count  int64
-}
-
-func parseCover(content string) []*covLine {
-	lines := strings.Split(content, "\n")
-	if len(lines) > 0 && strings.HasPrefix(lines[0], "mode:") {
-		lines = lines[1:]
-	}
-	covLines := make([]*covLine, 0, len(lines))
-	for _, line := range lines {
-		covLine := parseCovLine(line)
-		if covLine == nil {
-			continue
-		}
-		covLines = append(covLines, covLine)
-	}
-	return covLines
-}
-
-func parseCovLine(line string) *covLine {
-	idx := strings.LastIndex(line, " ")
-	if idx < 0 {
-		return nil
-	}
-	cnt, err := strconv.ParseInt(line[idx+1:], 10, 64)
-	if err != nil {
-		cnt = 0
-	}
-	return &covLine{
-		prefix: line[:idx],
-		count:  cnt,
-	}
-}
diff --git a/support/coverage/format.go b/support/coverage/format.go
new file mode 100644
index 00000000..f5ccc079
--- /dev/null
+++ b/support/coverage/format.go
@@ -0,0 +1,16 @@
+package coverage
+
+import (
+	"strconv"
+	"strings"
+)
+
+// mode can be: set
+func Format(mode string, lines []*CovLine) string {
+	strs := make([]string, 0, len(lines)+1)
+	strs = append(strs, "mode: "+mode)
+	for _, line := range lines {
+		strs = append(strs, line.Prefix+" "+strconv.FormatInt(line.Count, 10))
+	}
+	return strings.Join(strs, "\n")
+}
diff --git a/support/coverage/merge.go b/support/coverage/merge.go
new file mode 100644
index 00000000..96d3ae6a
--- /dev/null
+++ b/support/coverage/merge.go
@@ -0,0 +1,46 @@
+package coverage
+
+func Merge(covs ...[]*CovLine) []*CovLine {
+	if len(covs) == 0 {
+		return nil
+	}
+	if len(covs) == 1 {
+		return covs[0]
+	}
+	result := covs[0]
+	for i := 1; i < len(covs); i++ {
+		result = doMerge(result, covs[i])
+	}
+	return result
+}
+
+func Filter(covs []*CovLine, check func(line *CovLine) bool) []*CovLine {
+	n := len(covs)
+	j := 0
+	for i := 0; i < n; i++ {
+		if check(covs[i]) {
+			covs[j] = covs[i]
+			j++
+		}
+	}
+	return covs[:j]
+}
+
+func doMerge(linesA []*CovLine, linesB []*CovLine) []*CovLine {
+	for _, line := range linesB {
+		idx := -1
+		for i := 0; i < len(linesA); i++ {
+			if linesA[i].Prefix == line.Prefix {
+				idx = i
+				break
+			}
+		}
+		if idx < 0 {
+			linesA = append(linesA, line)
+		} else {
+			// fmt.Printf("add %s %d %d\n", a[idx].prefix, a[idx].count, line.count)
+			linesA[idx].Count += line.Count
+		}
+	}
+	return linesA
+}
diff --git a/support/coverage/parse.go b/support/coverage/parse.go
new file mode 100644
index 00000000..6a2ac874
--- /dev/null
+++ b/support/coverage/parse.go
@@ -0,0 +1,45 @@
+package coverage
+
+import (
+	"strconv"
+	"strings"
+)
+
+type CovLine struct {
+	Prefix string
+	Count  int64
+}
+
+const modePrefix = "mode:"
+
+func Parse(content string) (mode string, covLines []*CovLine) {
+	lines := strings.Split(content, "\n")
+	if len(lines) > 0 && strings.HasPrefix(lines[0], "mode:") {
+		mode = strings.TrimSpace(lines[0][len(modePrefix):])
+		lines = lines[1:]
+	}
+	covLines = make([]*CovLine, 0, len(lines))
+	for _, line := range lines {
+		covLine := ParseCovLine(line)
+		if covLine == nil {
+			continue
+		}
+		covLines = append(covLines, covLine)
+	}
+	return mode, covLines
+}
+
+func ParseCovLine(line string) *CovLine {
+	idx := strings.LastIndex(line, " ")
+	if idx < 0 {
+		return nil
+	}
+	cnt, err := strconv.ParseInt(line[idx+1:], 10, 64)
+	if err != nil {
+		cnt = 0
+	}
+	return &CovLine{
+		Prefix: line[:idx],
+		Count:  cnt,
+	}
+}
diff --git a/support/coverage/parse_test.go b/support/coverage/parse_test.go
new file mode 100644
index 00000000..a866ac8f
--- /dev/null
+++ b/support/coverage/parse_test.go
@@ -0,0 +1,15 @@
+package coverage
+
+import "testing"
+
+func TestParseCoverage(t *testing.T) {
+	mode, lines := Parse(`mode: set
+github.com/xhd2015/xgo/runtime/core/func.go:44.41,45.22 1 0`)
+	if mode != "set" {
+		t.Fatalf("expect mode to be %s, actual: %s", "set", mode)
+	}
+	if len(lines) != 1 {
+		t.Fatalf("len(lines): %d", len(lines))
+	}
+	// t.Logf("lines[0]: %v", lines[0])
+}