diff --git a/cmd/jqfmt/main.go b/cmd/jqfmt/main.go
index 6f8b916..d658405 100644
--- a/cmd/jqfmt/main.go
+++ b/cmd/jqfmt/main.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"path/filepath"
 	"strings"
 
 	"github.com/noperator/jqfmt"
@@ -24,17 +25,28 @@ func main() {
 	arr := flag.Bool("ar", false, "arrays")
 	oneLn := flag.Bool("o", false, "one line")
 	file := flag.String("f", "", "file")
+	write := flag.Bool("w", false, "write result to source file instead of stdout")
 	verbose := flag.Bool("v", false, "verbose")
 	// noHang := flag.Bool("nh", false, "no hanging indent")
+	flag.Usage = func() {
+		out := flag.CommandLine.Output()
+		fmt.Fprintf(out, "Usage: %s [options] [files...]\n\n", os.Args[0])
+		fmt.Fprintln(out, "Formats jq files or stdin. With -w, writes changes back to files.")
+		fmt.Fprintln(out, "If no files are specified, input is read from stdin and output is written to stdout.\n")
+		flag.PrintDefaults()
+	}
 	flag.Parse()
-	var from_stdin bool = false
 
 	if *verbose {
 		log.SetLevel(log.DebugLevel)
 	}
 
-	if *file == "" {
-		from_stdin = true
+	args := flag.Args()
+	if *file != "" && len(args) > 0 {
+		log.Fatal("cannot use -f with positional files")
+	}
+	if *write && *file == "" && len(args) == 0 {
+		log.Fatal("no files specified")
 	}
 
 	// var funcs []string
@@ -61,15 +73,68 @@ func main() {
 	})
 	assertErrorToNilf("invalid config: %v", err)
 
-	var jqBytes []byte
-	if from_stdin {
-		jqBytes, err = io.ReadAll(os.Stdin)
+	if *file == "" && len(args) == 0 {
+		jqBytes, err := io.ReadAll(os.Stdin)
+		assertErrorToNilf("could not read stdin: %v", err)
+		jqStrFmt, err := jqfmt.DoThing(string(jqBytes), cliCfg)
+		assertErrorToNilf("could not format jq: %v", err)
+		fmt.Print(jqStrFmt)
+		return
+	}
+
+	var files []string
+	if *file != "" {
+		files = []string{*file}
 	} else {
-		jqBytes, err = os.ReadFile(*file)
+		files = args
+	}
+
+	for _, path := range files {
+		jqBytes, err := os.ReadFile(path)
+		assertErrorToNilf("could not read file: %v", err)
+		jqStrFmt, err := jqfmt.DoThing(string(jqBytes), cliCfg)
+		assertErrorToNilf("could not format jq: %v", err)
+		if *write {
+			err = writeFileIfChanged(path, jqBytes, jqStrFmt)
+			assertErrorToNilf("could not write file: %v", err)
+		} else {
+			fmt.Print(jqStrFmt)
+		}
+	}
+}
+
+func writeFileIfChanged(path string, original []byte, formatted string) error {
+	if string(original) == formatted {
+		return nil
+	}
+
+	info, err := os.Stat(path)
+	if err != nil {
+		return err
+	}
+
+	dir := filepath.Dir(path)
+	tmp, err := os.CreateTemp(dir, ".jqfmt-*")
+	if err != nil {
+		return err
+	}
+	tmpName := tmp.Name()
+	if _, err := tmp.WriteString(formatted); err != nil {
+		tmp.Close()
+		os.Remove(tmpName)
+		return err
+	}
+	if err := tmp.Close(); err != nil {
+		os.Remove(tmpName)
+		return err
+	}
+	if err := os.Chmod(tmpName, info.Mode().Perm()); err != nil {
+		os.Remove(tmpName)
+		return err
+	}
+	if err := os.Rename(tmpName, path); err != nil {
+		os.Remove(tmpName)
+		return err
 	}
-	assertErrorToNilf("could not read file: %v", err)
-	jqStr := string(jqBytes)
-	jqStrFmt, err := jqfmt.DoThing(jqStr, cliCfg)
-	assertErrorToNilf("could not format jq: %v", err)
-	fmt.Print(jqStrFmt)
+	return nil
 }