diff --git a/manualsort.go b/manualsort.go
new file mode 100644
index 0000000..28f7f63
--- /dev/null
+++ b/manualsort.go
@@ -0,0 +1,122 @@
+// binary manualsort asks you at the CLI which of two things you like
+// better, repeatedly, and pukes up a list sorted accordingly.
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"log"
+	"os"
+	"slices"
+	"strings"
+)
+
+// handwritten merge sort because it minimizes comparisons, which are
+// the expensive part when asking a human for every comparison.
+// quicksort's "in-place" behavior isn't necessary.
+func merge(a, b []string) []string {
+	if len(a) == 0 {
+		return b
+	}
+	if len(b) == 0 {
+		return a
+	}
+	ret := make([]string, 0, len(a)+len(b))
+	for len(a) > 0 && len(b) > 0 {
+		if better(a[0], b[0]) {
+			ret = append(ret, a[0])
+			a = a[1:]
+		} else {
+			ret = append(ret, b[0])
+			b = b[1:]
+		}
+	}
+	if len(a) > 0 {
+		ret = append(ret, a...)
+	}
+	if len(b) > 0 {
+		ret = append(ret, b...)
+	}
+	return ret
+}
+
+var (
+	stdinReader *bufio.Reader
+	truthy      = []string{
+		"y", "yes", "1", "t", "true", "aye", "left", "up", "top", "first", "p",
+	}
+	falsey = []string{
+		"n", "no", "0", "2", "f", "false", "nay", "right", "down", "bottom", "second", "nil",
+	}
+)
+
+func better(first, second string) bool {
+	for {
+		fmt.Println()
+		fmt.Println("Is")
+		fmt.Println(first)
+		fmt.Println("better than")
+		fmt.Println(second)
+		fmt.Print("? > ")
+		reply, err := stdinReader.ReadString('\n')
+		if err != nil && len(reply) == 0 {
+			log.Fatalf("I/O error: %v", err)
+		}
+		reply = strings.TrimSpace(reply)
+		reply = strings.ToLower(reply)
+		if slices.Contains(truthy, reply) {
+			return true
+		}
+		if slices.Contains(falsey, reply) {
+			return false
+		}
+		fmt.Printf("Huh? I didn't understand %q. Answer \"y\" or \"n\".\n", reply)
+	}
+}
+
+func mergeSort(items []string) []string {
+	if len(items) <= 1 {
+		return items
+	}
+	midpoint := len(items) / 2
+	return merge(mergeSort(items[:midpoint]), mergeSort(items[midpoint:]))
+}
+
+func main() {
+	if len(os.Args) != 3 {
+		log.Fatal("wrong number of args, expected 2. Usage: manualsort <item list file> <output file path>")
+	}
+	ifile, err := os.Open(os.Args[1])
+	if err != nil {
+		log.Fatalf("can't open %q: %v.", os.Args[1], err)
+	}
+	ofile, err := os.OpenFile(os.Args[2], os.O_CREATE|os.O_EXCL, 0600)
+	if err != nil {
+		log.Fatalf("can't exclusively create %q: %v.", os.Args[2], err)
+	}
+	stdinReader = bufio.NewReader(os.Stdin)
+
+	var items []string
+	scanner := bufio.NewScanner(ifile)
+	for scanner.Scan() {
+		if t := strings.TrimSpace(scanner.Text()); len(t) > 0 {
+			items = append(items, t)
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		log.Fatalf("can't read %q: %v", os.Args[1], err)
+	}
+
+	sorted := mergeSort(items)
+	fmt.Println("Sorted. Saving...")
+	obuf := bufio.NewWriter(ofile)
+	for i, s := range sorted {
+		_, err := obuf.WriteString(fmt.Sprintf("%6d %s\n", i+1, s))
+		if err != nil {
+			log.Printf("error saving %d (%s): %v\n", i+1, s, err)
+		}
+	}
+	obuf.Flush()
+	ofile.Sync()
+	ofile.Close()
+}