diff --git a/00-META/checks/index_test.go b/00-META/checks/index_test.go
new file mode 100644
index 00000000..ca4b7871
--- /dev/null
+++ b/00-META/checks/index_test.go
@@ -0,0 +1,93 @@
+package checks
+
+import (
+	"fmt"
+	"io/fs"
+	"regexp"
+	"strings"
+	"testing"
+	"testing/fstest"
+)
+
+// The reading order of the decision records (index.py until ADR 0527): its topics are written in
+// 02-DECISIONS/README.md, its records are not. The knowledge base reads these lines and refuses a record whose
+// topic is not one of them, so the form is a contract; a topic's records are `knowledge-base.holds` with that
+// topic, never stored here (ADR 0248, issue 297).
+
+const readmeOfDecisions = "02-DECISIONS/README.md"
+
+// A topic line: `1. **Label** — `topic: name`. ...`
+var topicLineRx = regexp.MustCompile(`(?m)^\d+\.\s+\*\*([^*]+)\*\*\s+—\s+` + "`topic:\\s*([^`]+)`")
+
+// What a stored list looks like: the old markers, or a line of the list index.py used to print.
+var storedLists = []struct {
+	rx   *regexp.Regexp
+	what string
+}{
+	{regexp.MustCompile(`<!--\s*index:(start|end)\s*-->`), "an index marker"},
+	{regexp.MustCompile(`(?m)^- \*\*\d{4}\*\* — \[`), "a line of a generated list"},
+}
+
+func readingOrder(text string) []string {
+	var topics []string
+	for _, m := range topicLineRx.FindAllStringSubmatch(text, -1) {
+		topics = append(topics, strings.TrimSpace(m[2]))
+	}
+	return topics
+}
+
+func checkIndex(fsys fs.FS) []string {
+	text := readFile(fsys, readmeOfDecisions)
+	topics := readingOrder(text)
+	var out []string
+	if len(topics) == 0 {
+		out = append(out, "index: "+readmeOfDecisions+" writes no reading order: no line of the form '1. **Label** — `topic: name`. ...'; "+
+			"the knowledge base refuses every record without it")
+	}
+	seen := map[string]bool{}
+	for _, topic := range topics {
+		if seen[topic] {
+			out = append(out, fmt.Sprintf("index: %s names a topic twice in its reading order: %s", readmeOfDecisions, topic))
+			break
+		}
+		seen[topic] = true
+	}
+	for _, s := range storedLists {
+		if s.rx.MatchString(text) {
+			out = append(out, fmt.Sprintf("index: %s stores a list of records (%s). The records live in the knowledge base, and a topic's list is "+
+				"`knowledge-base.holds` with that topic", readmeOfDecisions, s.what))
+		}
+	}
+	return out
+}
+
+func TestIndexReadingOrderIsWrittenAndStoresNoList(t *testing.T) {
+	expectNone(t, checkIndex(rootFS()))
+	if n := len(readingOrder(readFile(rootFS(), readmeOfDecisions))); n == 0 {
+		t.Error("the reading order has no topic")
+	}
+}
+
+const sound = "1. **One** — `topic: one`. x\n2. **Two** — `topic: two`. y\n"
+
+func TestIndexCatchesAMissingReadingOrder(t *testing.T) {
+	expectProblem(t, checkIndex(fstest.MapFS{readmeOfDecisions: doc("nothing written here\n")}), "writes no reading order")
+}
+
+func TestIndexCatchesADuplicateTopic(t *testing.T) {
+	broken := fstest.MapFS{readmeOfDecisions: doc(sound + "3. **Again** — `topic: one`. z\n")}
+	expectProblem(t, checkIndex(broken), "names a topic twice")
+}
+
+func TestIndexCatchesAStoredList(t *testing.T) {
+	for what, stored := range map[string]string{
+		"an index marker":            "<!-- index:start -->\n",
+		"a line of a generated list": "- **0001** — [a title](x.md)\n",
+	} {
+		expectProblem(t, checkIndex(fstest.MapFS{readmeOfDecisions: doc(sound + stored)}), what)
+	}
+}
+
+func TestIndexAcceptsASoundReadme(t *testing.T) {
+	expectNone(t, checkIndex(fstest.MapFS{readmeOfDecisions: doc(sound)}))
+}