look at the code if you want to know what i did

nbt/nbt.go

@@ -291,6 +291,8 @@ func readPayload(id int8, r io.Reader) (ret any, err error) {
 	return
 }
 
+var UnknownTagTypeErr = errors.New("unknown nbt type")
+
 func writePayload(v any, w io.Writer) (err error) {
 	switch v := v.(type) {
 	case struct{}:
@@ -361,7 +363,7 @@ func writePayload(v any, w io.Writer) (err error) {
 		}
 		err = binary.Write(w, Order, End)
 	default:
-		err = errors.New("unknown nbt type")
+		err = UnknownTagTypeErr
 	}
 	return
 }

nbt/snbt.go

@@ -0,0 +1,91 @@
+package nbt
+
+import (
+	"fmt"
+	"io"
+)
+
+// PrintSNBTAny documented at https://minecraft.wiki/w/NBT_format#SNBT_format
+func PrintSNBTAny(t any, w io.Writer) (err error) {
+	switch t := t.(type) {
+	case int8:
+		_, err = fmt.Fprintf(w, "%vB", t)
+	case bool:
+		_, err = fmt.Fprintf(w, "%v", t)
+	case int16:
+		_, err = fmt.Fprintf(w, "%vS", t)
+	case int32:
+		_, err = fmt.Fprintf(w, "%vI", t)
+	case int64:
+		_, err = fmt.Fprintf(w, "%vL", t)
+	case float32:
+		_, err = fmt.Fprintf(w, "%vF", t)
+	case float64:
+		_, err = fmt.Fprintf(w, "%vD", t)
+	case string:
+		_, err = fmt.Fprintf(w, "%q", t)
+	case []any:
+		_, err = fmt.Fprintf(w, "[")
+		for _, v := range t {
+			err = PrintSNBTAny(v, w)
+			if err != nil {
+				return
+			}
+			_, err = fmt.Fprintf(w, ",")
+		}
+		_, err = fmt.Fprintf(w, "]")
+	case map[string]any:
+		_, err = fmt.Fprintf(w, "{")
+		for k, v := range t {
+			_, err = fmt.Fprintf(w, "%q:,", k)
+			err = PrintSNBTAny(v, w)
+			if err != nil {
+				return
+			}
+			_, err = fmt.Fprintf(w, ",")
+		}
+		_, err = fmt.Fprintf(w, "}")
+	case []int8:
+		_, err = fmt.Fprintf(w, "[B;")
+		if err != nil {
+			return
+		}
+		for _, v := range t {
+			err = PrintSNBTAny(v, w)
+			if err != nil {
+				return
+			}
+			_, err = fmt.Fprintf(w, ",")
+		}
+		_, err = fmt.Fprintf(w, "]")
+	case []int32:
+		_, err = fmt.Fprintf(w, "[I;")
+		if err != nil {
+			return
+		}
+		for _, v := range t {
+			err = PrintSNBTAny(v, w)
+			if err != nil {
+				return
+			}
+			_, err = fmt.Fprintf(w, ",")
+		}
+		_, err = fmt.Fprintf(w, "]")
+	case []int64:
+		_, err = fmt.Fprintf(w, "[L;")
+		if err != nil {
+			return
+		}
+		for _, v := range t {
+			err = PrintSNBTAny(v, w)
+			if err != nil {
+				return
+			}
+			_, err = fmt.Fprintf(w, ",")
+		}
+		_, err = fmt.Fprintf(w, "]")
+	default:
+		err = UnknownTagTypeErr
+	}
+	return
+}

nbt/snbt_test.go

@@ -0,0 +1,23 @@
+package nbt
+
+import (
+	"bytes"
+	_ "embed"
+	"testing"
+)
+
+//go:embed testdata/top_0_20.nbt
+var topSNBT []byte
+
+func TestPrintSNBTAny(t *testing.T) {
+	n, err := ReadFile(bytes.NewReader(topSNBT))
+	if err != nil {
+		panic(err)
+	}
+	bb := bytes.NewBuffer(nil)
+	err = PrintSNBTAny(n.Value, bb)
+	if err != nil {
+		panic(err)
+	}
+	t.Log(bb.String())
+}