diff --git a/core/trino-spi/src/main/java/io/trino/spi/Experimental.java b/core/trino-spi/src/main/java/io/trino/spi/Experimental.java
index 3867e67245ad..33781036b1e5 100644
--- a/core/trino-spi/src/main/java/io/trino/spi/Experimental.java
+++ b/core/trino-spi/src/main/java/io/trino/spi/Experimental.java
@@ -35,6 +35,8 @@
 {
     /**
      * When the community expects the SPI will be finalized, but this date may be extended.
+     * <p>
+     * The value should be a date in ISO-8601 format uuuu-MM-dd.
      */
     String eta();
 }