diff --git a/action.yml b/action.yml
index 379efed..f9e1a3e 100644
--- a/action.yml
+++ b/action.yml
@@ -7,7 +7,7 @@ branding:
 
 inputs:
   since:
-    description: Only advisories created after this date (2026-10-22 or RFC 3339) are triaged. Required with `comment: true` unless `advisory` is set, every advisory in triage otherwise.
+    description: "Only advisories created after this date (2026-10-22 or RFC 3339) are triaged. Required with `comment: true` unless `advisory` is set, every advisory in triage otherwise."
     required: false
   advisory:
     description: Triage this GHSA only, whatever its state and creation date.
diff --git a/cmd/tamis/main_test.go b/cmd/tamis/main_test.go
index d77a7cf..2790570 100644
--- a/cmd/tamis/main_test.go
+++ b/cmd/tamis/main_test.go
@@ -4,11 +4,13 @@ import (
 	"context"
 	"io"
 	"log/slog"
+	"os"
 	"testing"
 	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"go.yaml.in/yaml/v3"
 )
 
 func TestParseSince(t *testing.T) {
@@ -80,3 +82,22 @@ func TestRunValidatesConfiguration(t *testing.T) {
 		})
 	}
 }
+
+// GitHub refuses to run an action whose manifest does not parse, with no test of its own to tell.
+func TestActionManifestParses(t *testing.T) {
+	data, err := os.ReadFile("../../action.yml")
+	require.NoError(t, err)
+	var manifest struct {
+		Inputs map[string]struct {
+			Description string `yaml:"description"`
+		} `yaml:"inputs"`
+	}
+
+	require.NoError(t, yaml.Unmarshal(data, &manifest))
+
+	require.NotEmpty(t, manifest.Inputs)
+	for name, input := range manifest.Inputs {
+		require.NotEmpty(t, input.Description, "the %s input lost its description", name)
+	}
+	require.Error(t, yaml.Unmarshal([]byte("inputs:\n  since:\n    description: Required with `comment: true` unless set.\n"), &manifest), "the test would not catch the colon that broke the manifest")
+}
diff --git a/go.mod b/go.mod
index a295f57..d070c21 100644
--- a/go.mod
+++ b/go.mod
@@ -8,6 +8,7 @@ require (
 	github.com/git-pkgs/cwe v0.1.1
 	github.com/openai/openai-go/v3 v3.85.1
 	github.com/stretchr/testify v1.12.1
+	go.yaml.in/yaml/v3 v3.0.5
 	golang.org/x/sync v0.24.0
 )
 
@@ -39,7 +40,6 @@ require (
 	go.opentelemetry.io/otel/log v1.47.0 // indirect
 	go.opentelemetry.io/otel/metric v1.47.0 // indirect
 	go.opentelemetry.io/otel/trace v1.47.0 // indirect
-	go.yaml.in/yaml/v3 v3.0.5 // indirect
 	golang.org/x/mod v0.42.0 // indirect
 	golang.org/x/sys v0.49.0 // indirect
 	golang.org/x/term v0.47.0 // indirect