diff --git a/tools/dumptab/main.go b/tools/dumptab/main.go
new file mode 100644
index 0000000..c53f776
--- /dev/null
+++ b/tools/dumptab/main.go
@@ -0,0 +1,58 @@
+// Command dumptab writes one sheet tab to a local CSV file.
+package main
+
+import (
+	"context"
+	"encoding/csv"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"strings"
+
+	"heliosian/internal/data"
+	"google.golang.org/api/option"
+	"google.golang.org/api/sheets/v4"
+)
+
+func main() {
+	sheet := flag.String("sheet", "", "spreadsheet id")
+	tab := flag.String("tab", "", "tab title")
+	out := flag.String("out", "", "output csv path")
+	flag.Parse()
+	if *sheet == "" || *tab == "" || *out == "" {
+		log.Fatal("[ERROR] -sheet, -tab, and -out are required")
+	}
+	svc, err := sheets.NewService(context.Background(),
+		option.WithCredentialsFile(data.KeyFile),
+		option.WithScopes(sheets.SpreadsheetsReadonlyScope))
+	if err != nil {
+		log.Fatalf("[ERROR] create sheets client: %v", err)
+	}
+	resp, err := svc.Spreadsheets.Values.Get(*sheet, "'"+strings.ReplaceAll(*tab, "'", "''")+"'").Do()
+	if err != nil {
+		log.Fatalf("[ERROR] read tab %s: %v", *tab, err)
+	}
+	f, err := os.Create(*out)
+	if err != nil {
+		log.Fatalf("[ERROR] create %s: %v", *out, err)
+	}
+	w := csv.NewWriter(f)
+	for _, row := range resp.Values {
+		record := make([]string, len(row))
+		for i, cell := range row {
+			record[i] = fmt.Sprint(cell)
+		}
+		if err := w.Write(record); err != nil {
+			log.Fatalf("[ERROR] write row: %v", err)
+		}
+	}
+	w.Flush()
+	if err := w.Error(); err != nil {
+		log.Fatalf("[ERROR] flush csv: %v", err)
+	}
+	if err := f.Close(); err != nil {
+		log.Fatalf("[ERROR] close %s: %v", *out, err)
+	}
+	log.Printf("wrote %d rows to %s", len(resp.Values), *out)
+}
diff --git a/tools/writetab/main.go b/tools/writetab/main.go
new file mode 100644
index 0000000..3b26178
--- /dev/null
+++ b/tools/writetab/main.go
@@ -0,0 +1,86 @@
+// Command writetab writes a local CSV into an empty sheet tab below its matching header row.
+package main
+
+import (
+	"context"
+	"encoding/csv"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"strings"
+
+	"heliosian/internal/data"
+	"google.golang.org/api/option"
+	"google.golang.org/api/sheets/v4"
+)
+
+func main() {
+	sheet := flag.String("sheet", "", "spreadsheet id")
+	tab := flag.String("tab", "", "tab title")
+	in := flag.String("in", "", "input csv path (first row must match the tab header)")
+	appendRows := flag.Bool("append", false, "append below existing rows instead of requiring an empty tab")
+	flag.Parse()
+	if *sheet == "" || *tab == "" || *in == "" {
+		log.Fatal("[ERROR] -sheet, -tab, and -in are required")
+	}
+	f, err := os.Open(*in)
+	if err != nil {
+		log.Fatalf("[ERROR] open %s: %v", *in, err)
+	}
+	records, err := csv.NewReader(f).ReadAll()
+	if err != nil {
+		log.Fatalf("[ERROR] read %s: %v", *in, err)
+	}
+	if err := f.Close(); err != nil {
+		log.Fatalf("[ERROR] close %s: %v", *in, err)
+	}
+	if len(records) < 2 {
+		log.Fatalf("[ERROR] %s has no data rows", *in)
+	}
+	svc, err := sheets.NewService(context.Background(),
+		option.WithCredentialsFile(data.KeyFile),
+		option.WithScopes(sheets.SpreadsheetsScope))
+	if err != nil {
+		log.Fatalf("[ERROR] create sheets client: %v", err)
+	}
+	quoted := "'" + strings.ReplaceAll(*tab, "'", "''") + "'"
+	resp, err := svc.Spreadsheets.Values.Get(*sheet, quoted).Do()
+	if err != nil {
+		log.Fatalf("[ERROR] read tab %s: %v", *tab, err)
+	}
+	if len(resp.Values) == 0 {
+		log.Fatalf("[ERROR] tab %s has no header row", *tab)
+	}
+	if !*appendRows && len(resp.Values) != 1 {
+		log.Fatalf("[ERROR] tab %s has %d rows; want exactly the header row", *tab, len(resp.Values))
+	}
+	header := make([]string, len(resp.Values[0]))
+	for i, cell := range resp.Values[0] {
+		header[i] = strings.TrimSpace(fmt.Sprint(cell))
+	}
+	if strings.Join(header, "\x00") != strings.Join(records[0], "\x00") {
+		log.Fatalf("[ERROR] header mismatch:\n tab: %q\n csv: %q", header, records[0])
+	}
+	values := make([][]interface{}, len(records)-1)
+	for i, rec := range records[1:] {
+		row := make([]interface{}, len(rec))
+		for j, cell := range rec {
+			row[j] = cell
+		}
+		values[i] = row
+	}
+	if *appendRows {
+		_, err = svc.Spreadsheets.Values.Append(*sheet, quoted, &sheets.ValueRange{
+			Values: values,
+		}).ValueInputOption("RAW").InsertDataOption("INSERT_ROWS").Do()
+	} else {
+		_, err = svc.Spreadsheets.Values.Update(*sheet, quoted+"!A2", &sheets.ValueRange{
+			Values: values,
+		}).ValueInputOption("RAW").Do()
+	}
+	if err != nil {
+		log.Fatalf("[ERROR] write rows: %v", err)
+	}
+	log.Printf("wrote %d rows to %s", len(values), *tab)
+}