--- a/pkg/controllers/report.go	Sat May 29 17:19:03 2021 +0200
+++ b/pkg/controllers/report.go	Sun May 30 01:26:36 2021 +0200
@@ -19,15 +19,86 @@
 	"net/http"
 	"os"
 	"path/filepath"
+	"sort"
+	"strings"
 
 	"gemma.intevation.de/gemma/pkg/config"
 	"gemma.intevation.de/gemma/pkg/middleware"
 	"gemma.intevation.de/gemma/pkg/xlsx"
 
+	mw "gemma.intevation.de/gemma/pkg/middleware"
+
 	"github.com/360EntSecGroup-Skylar/excelize/v2"
 	"github.com/gorilla/mux"
 )
 
+func listReports(req *http.Request) (jr mw.JSONResult, err error) {
+	path := config.ReportPath()
+	if path == "" {
+		err = mw.JSONError{
+			Code:    http.StatusNotFound,
+			Message: http.StatusText(http.StatusNotFound),
+		}
+		return
+	}
+
+	// This would be easier with Go 1.16+.
+
+	dir, err := os.Open(path)
+	if err != nil {
+		log.Printf("error: %v\n", err)
+		err = mw.JSONError{
+			Code:    http.StatusInternalServerError,
+			Message: "Listing report templates failed.",
+		}
+		return
+	}
+	defer dir.Close()
+	files, err := dir.Readdirnames(-1)
+	if err != nil {
+		log.Printf("error: %v\n", err)
+		err = mw.JSONError{
+			Code:    http.StatusInternalServerError,
+			Message: "Listing report templates failed.",
+		}
+		return
+	}
+
+	pairs := map[string]int{}
+
+all:
+	for _, file := range files {
+		var mask int
+		switch {
+		case strings.HasSuffix(file, ".xlsx"):
+			mask = 1
+		case strings.HasSuffix(file, ".yaml"):
+			mask = 2
+		default:
+			continue all
+		}
+		basename := filepath.Base(file)
+		name := strings.TrimSuffix(basename, filepath.Ext(basename))
+		pairs[name] |= mask
+	}
+
+	var reports []string
+	for name, mask := range pairs {
+		if mask == 3 {
+			reports = append(reports, name)
+		}
+	}
+	sort.Strings(reports)
+
+	out := struct {
+		Reports []string `json:"reports"`
+	}{
+		Reports: reports,
+	}
+	jr = mw.JSONResult{Result: out}
+	return
+}
+
 func report(rw http.ResponseWriter, req *http.Request) {
 
 	path := config.ReportPath()

--- a/pkg/controllers/routes.go	Sat May 29 17:19:03 2021 +0200
+++ b/pkg/controllers/routes.go	Sun May 30 01:26:36 2021 +0200
@@ -324,6 +324,12 @@
 
 	// Handler for reporting
 
+	api.Handle("/data/reports",
+		waterwayAdmin(&mw.JSONHandler{
+			Handle: listReports,
+			NoConn: true,
+		})).Methods(http.MethodGet)
+
 	api.Handle("/data/report/{name:[a-zA-Z0-9_]+}", waterwayAdmin(
 		mw.DBConn(http.HandlerFunc(report)))).Methods(http.MethodGet)