diff --git a/cmd/cmd.go b/cmd/cmd.go
index 5f2345d..670f342 100644
--- a/cmd/cmd.go
+++ b/cmd/cmd.go
@@ -8,5 +8,6 @@ const (
 	Last Subcommand = "last"
 	Sort Subcommand = "sort"
 	Cat  Subcommand = "cat"
+	Mv   Subcommand = "mv"
 	Help Subcommand = "help"
 )
diff --git a/mv/mv.go b/mv/mv.go
new file mode 100644
index 0000000..de901b8
--- /dev/null
+++ b/mv/mv.go
@@ -0,0 +1,97 @@
+package mv
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strings"
+
+	"github.com/brtholomy/um/go/cat"
+	"github.com/brtholomy/um/go/cmd"
+	"github.com/brtholomy/um/go/flags"
+	"github.com/brtholomy/um/go/next"
+	"github.com/brtholomy/um/go/pipe"
+)
+
+const (
+	CMD     = cmd.Mv
+	SUMMARY = "rename an um file descriptor field while updating its header"
+)
+
+type options struct {
+	Filename   flags.Arg
+	Descriptor flags.Arg
+	Help       flags.Flag[bool]
+}
+
+func initOpts() options {
+	return options{
+		flags.Arg{"", "old filename"},
+		flags.Arg{"", "new descriptor"},
+		flags.Flag[bool]{"--help", "-h", false, "show help"},
+	}
+}
+
+// generates new filename and its content with updated H1 header
+func newNameAndContent(olds string, opts options) (name string, content string, err error) {
+	// name and title
+	num, err := next.NumFromLast(opts.Filename.Val)
+	if err != nil {
+		return "", "", err
+	}
+	name = fmt.Sprintf("%s.%s.md", num, opts.Descriptor.Val)
+	title := fmt.Sprintf("# %s", name)
+
+	// content
+	head, tail, ok := strings.Cut(olds, pipe.Newline)
+	// the file has no newline at all?
+	if !ok {
+		tail = head
+	}
+	// there was no title in the original
+	if !strings.HasPrefix(head, cat.H1) {
+		tail = olds
+	}
+	return name, fmt.Sprintf("%s%s%s", title, pipe.Newline, tail), nil
+}
+
+// effectively does a mv to the new filename, while updating the H1 header to match.
+func mv(opts options) error {
+	oldb, err := os.ReadFile(opts.Filename.Val)
+	if err != nil {
+		return err
+	}
+	olds := string(oldb)
+
+	name, content, err := newNameAndContent(olds, opts)
+	if err != nil {
+		return err
+	}
+
+	// create
+	newf, err := os.Create(name)
+	if err != nil {
+		return err
+	}
+	defer newf.Close()
+	_, err = newf.WriteString(content)
+	if err != nil {
+		return err
+	}
+
+	// destroy
+	err = os.Remove(opts.Filename.Val)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func Mv(args []string) {
+	opts := initOpts()
+	flags.ParseArgs(CMD, SUMMARY, args, &opts)
+	err := mv(opts)
+	if err != nil {
+		log.Fatalf("um %s: %v", CMD, err)
+	}
+}
diff --git a/next/next.go b/next/next.go
index ccab0dc..f012758 100644
--- a/next/next.go
+++ b/next/next.go
@@ -38,7 +38,7 @@ func initOpts() options {
 
 // takes the complete last file string
 // returns the number as string
-func numFromLast(l string) (string, error) {
+func NumFromLast(l string) (string, error) {
 	res := fileRegexp.FindStringSubmatch(l)
 	num := ""
 	if len(res) < 2 {
@@ -51,7 +51,7 @@ func numFromLast(l string) (string, error) {
 // takes the complete last file string and new descriptor
 // returns the complete next file string
 func next(last string, desc string) (string, error) {
-	num, err := numFromLast(last)
+	num, err := NumFromLast(last)
 	if err != nil {
 		return "", err
 	}
diff --git a/um.go b/um.go
index 3f055ae..c593c83 100644
--- a/um.go
+++ b/um.go
@@ -8,12 +8,13 @@ import (
 	"github.com/brtholomy/um/go/cat"
 	"github.com/brtholomy/um/go/cmd"
 	"github.com/brtholomy/um/go/last"
+	"github.com/brtholomy/um/go/mv"
 	"github.com/brtholomy/um/go/next"
 	"github.com/brtholomy/um/go/sort"
 	"github.com/brtholomy/um/go/tag"
 )
 
-var helpShort string = fmt.Sprintf("um [%s | %s | %s | %s | %s | %s]", cmd.Next, cmd.Last, cmd.Tag, cmd.Cat, cmd.Sort, cmd.Help)
+var helpShort string = fmt.Sprintf("um [%s | %s | %s | %s | %s | %s | %s]", cmd.Next, cmd.Last, cmd.Tag, cmd.Cat, cmd.Sort, cmd.Mv, cmd.Help)
 var helpLong string = fmt.Sprintf(`%s
 
 An (U)ltralight database for (M)arkdown composition.
@@ -47,6 +48,8 @@ func main() {
 		cat.Cat(args)
 	case cmd.Sort:
 		sort.Sort(args)
+	case cmd.Mv:
+		mv.Mv(args)
 	case cmd.Help:
 		log.Fatalln(helpLong)
 	default: