add readme

README.md

@@ -0,0 +1,24 @@
+# umadump-gametora
+
+Convert [Umadump](https://github.com/Werseter/umadump) exports into [GameTora collection](https://gametora.com/umamusume/collection-tracker) backups.
+
+This program is meant to be a temporary helper until GameTora has full Umadump import built in, which should be soon.
+Therefore, it does not provide a pretty UI.
+
+## Usage
+
+With a recent Go toolchain installed, open a terminal and run:
+
+```
+umadump
+go run git.sunturtle.xyz/zephyr/umadump-gametora@latest
+```
+
+If you run umadump in a different directory, pass that directory with `-dump` on the `go run` line.
+E.g., I run umadump in `C:\Users\zephyr\Downloads`, so the command I use is
+
+```
+go run git.sunturtle.xyz/zephyr/umadump-gametora@latest -dump C:\Users\zephyr\Downloads
+```
+
+This writes the collection to a file like `uma-col-all-2026-05-06.json` which you can use with the `Import from a file instead` link in the `Import` section of the `Backup` menu on the GameTora collection tracker page.

umadump-gametora.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"encoding/json"
 	"flag"
+	"fmt"
 	"io"
 	"log/slog"
 	"net/http"
@@ -88,12 +89,13 @@ func filejson[T any](path string) ([]T, error) {
 }
 
 func main() {
+	ts := time.Now().UTC().Format(time.DateOnly) // can't use RFC3339 because :s in filename
 	var (
 		dumpDir string
 		out     string
 	)
 	flag.StringVar(&dumpDir, "dump", ".", "`dir`ectory containing umadump output files")
-	flag.StringVar(&out, "o", "", "output `file` (default stdout)")
+	flag.StringVar(&out, "o", fmt.Sprintf("uma-col-all-%s.json", ts), "output `file` (stdout if empty)")
 	flag.Parse()
 
 	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt)
@@ -142,7 +144,7 @@ func main() {
 		Game:      "umamusume",
 		Type:      "collection",
 		Version:   4,
-		Timestamp: time.Now().String(),
+		Timestamp: ts,
 		Servers: map[string]CollectionServer{
 			"en": {
 				CharCards: charaLevels,