diff --git a/internal/errkind/errkind_test.go b/internal/errkind/errkind_test.go
new file mode 100644
index 0000000..cba5ce5
--- /dev/null
+++ b/internal/errkind/errkind_test.go
@@ -0,0 +1,64 @@
+package errkind_test
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+	"net/url"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"git.d-ma.be/mathias/tapir/internal/errkind"
+)
+
+// Of reduces an error to a short kind that is safe to log, store and show: it never
+// carries the error's own text, because that text can hold a provider's response body, a
+// file path or a word from a private transcript (ADR-035 review F3, F5).
+
+type statusErr struct{ code int }
+
+func (e statusErr) Error() string {
+	return fmt.Sprintf("gateway said: %d and echoed the transcript", e.code)
+}
+func (e statusErr) HTTPStatus() int { return e.code }
+
+type timeoutNet struct{}
+
+func (timeoutNet) Error() string   { return "i/o timeout to 10.0.0.1" }
+func (timeoutNet) Timeout() bool   { return true }
+func (timeoutNet) Temporary() bool { return true }
+
+func TestOf_ReducesAnErrorToAKindAndNeverItsText(t *testing.T) {
+	tests := []struct {
+		name string
+		err  error
+		want string
+	}{
+		{"nothing", nil, ""},
+		{"a deadline", context.DeadlineExceeded, "timeout"},
+		{"a wrapped deadline", fmt.Errorf("transcribe: %w", context.DeadlineExceeded), "timeout"},
+		{"a cancellation", fmt.Errorf("job: %w", context.Canceled), "canceled"},
+		{"an HTTP status", statusErr{code: 502}, "http_502"},
+		{"a wrapped HTTP status", fmt.Errorf("model: %w", statusErr{code: 400}), "http_400"},
+		{"a network timeout", timeoutNet{}, "timeout"},
+		{"a network failure", &net.OpError{Op: "dial", Err: errors.New("connection refused")}, "network"},
+		{"a url error wrapping a refusal", &url.Error{Op: "Post", URL: "http://gateway/secret-path", Err: errors.New("refused")}, "network"},
+		{"anything else", errors.New("moov atom not found in /spool/upload-555"), "error"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.want, errkind.Of(tt.err))
+		})
+	}
+}
+
+func TestOf_AKindCarriesNoWordFromTheError(t *testing.T) {
+	err := fmt.Errorf("convert /spool/upload-555: %w", errors.New("Anders ansvarar för virket"))
+
+	got := errkind.Of(err)
+
+	assert.NotContains(t, got, "Anders")
+	assert.NotContains(t, got, "spool")
+}