diff --git a/README.md b/README.md
index 8282138..4ea45c0 100644
--- a/README.md
+++ b/README.md
@@ -36,13 +36,13 @@ Assume some GitHub actions workflow have lines like follows
 Then you can call selfup as this
 
 ```bash
-selfup run --prefix='# selfup ' .github/workflows/*.yml
+selfup run .github/workflows/*.yml
 ```
 
 You can check the running plans with `list` subcommand
 
 ```console
-> selfup list --prefix='# selfup ' .github/workflows/*.yml
+> selfup list .github/workflows/*.yml
   .github/workflows/lint.yml:17: 0.40.2
 ✓ .github/workflows/release.yml:37: 1.20.0 => 1.42.9
   .github/workflows/lint.yml:24: 1.16.12
@@ -63,8 +63,10 @@ Changed from v0.0.3
 
 ### Options
 
-- `--skip-by`: skips to parse JSON and runs if the line includes this string
-- `--no-color`: avoid to wrap colors even if executed in terminal
+- `--prefix`: Set customized prefix to begin the JSON
+- `--skip-by`: Skips to parse JSON and runs if the line includes this string
+- `--no-color`: Avoid to wrap colors even if executed in terminal
+- `--version`: Print the version
 
 ## Motivation
 
diff --git a/cmd/selfup/main.go b/cmd/selfup/main.go
index fbb5613..ece62a5 100644
--- a/cmd/selfup/main.go
+++ b/cmd/selfup/main.go
@@ -22,17 +22,18 @@ var (
 )
 
 func main() {
+	versionFlag := flag.Bool("version", false, "print the version of this program")
+
 	sharedFlags := flag.NewFlagSet("run|list", flag.ExitOnError)
-	prefixFlag := sharedFlags.String("prefix", "", "prefix to write json")
+	prefixFlag := sharedFlags.String("prefix", " selfup ", "prefix to begin json")
 	skipByFlag := sharedFlags.String("skip-by", "", "skip to run if the line contains this string")
 	noColorFlag := sharedFlags.Bool("no-color", false, "disable color output")
-	versionFlag := flag.Bool("version", false, "print the version of this program")
 
 	const usage = `Usage: selfup [SUB] [OPTIONS] [PATH]...
 
-$ selfup run --prefix='# selfup ' .github/workflows/*.yml
-$ selfup run --prefix='# selfup ' --skip-by='nix run' .github/workflows/*.yml
-$ selfup list --prefix='# selfup ' .github/workflows/*.yml
+$ selfup run .github/workflows/*.yml
+$ selfup run --prefix='# Update with this json: ' --skip-by='nix run' .github/workflows/*.yml
+$ selfup list .github/workflows/*.yml
 $ selfup --version
 `
 
diff --git a/internal/selfup.go b/internal/selfup.go
index 496be2b..ea4acdc 100644
--- a/internal/selfup.go
+++ b/internal/selfup.go
@@ -50,11 +50,12 @@ func Update(path string, prefix string, skipBy string, isColor bool) (Result, er
 			newLines = append(newLines, line)
 			continue
 		}
-		head, tail, found := strings.Cut(line, prefix)
+		head, tail, found := strings.Cut(line, prefix+"{")
 		if !found {
 			newLines = append(newLines, line)
 			continue
 		}
+		tail = "{" + tail
 
 		def := &Definition{}
 		totalCount += 1