diff --git a/internal/apiclient.go b/internal/apiclient.go
new file mode 100644
index 0000000..518db40
--- /dev/null
+++ b/internal/apiclient.go
@@ -0,0 +1,18 @@
+package internal
+
+import "os"
+
+// APIClient is a minimal client for the (future) demo API.
+type APIClient struct {
+	APIKey string
+}
+
+// NewAPIClientFromEnv builds a client using the API key from the
+// DEMO_API_KEY environment variable. Returns an error if it's unset.
+func NewAPIClientFromEnv() (*APIClient, error) {
+	key := os.Getenv("DEMO_API_KEY")
+	if key == "" {
+		return nil, errMissingAPIKey
+	}
+	return &APIClient{APIKey: key}, nil
+}
diff --git a/internal/errors.go b/internal/errors.go
new file mode 100644
index 0000000..ff8b708
--- /dev/null
+++ b/internal/errors.go
@@ -0,0 +1,5 @@
+package internal
+
+import "errors"
+
+var errMissingAPIKey = errors.New("DEMO_API_KEY environment variable is not set")