Does the Horizon Walker ranger's Portal Lore feature detect portals that are currently inactive?

Question

The Horizon Walker Ranger subclass gains Portal Lore ability (quoted from UA; I don't have Xanthar's Guide to compare the feature):

Portal Lore

At 3rd level, you gain the ability to detect the presence of planar portals. As an action, you detect the distance and direction to any planar portals within 1,000 feet of you. You also sense which plane of existence each portal leads to. However, if magic obscures any details of a portal, this feature doesn’t reveal them.

On DMG page 45, it says that "most portals don't stand open all the time" and goes on to give some example conditions for a portal to become open.

Can the Portal Lore feature be used to detect an inactive portal, or do they fail to show up unless the Ranger happens to use the ability when the portal is open?

Obviously, a GM can make a ruling either way, but I'm looking for any information, including from other editions of D&D, that would inform a such a ruling.

Answer 1

Yes, this ability should work on closed portals.

For reference, the Horizon Walker's ability as found in Xanathar's Guide to Everything is called Detect Portal. Its description states:

At 3rd level, you gain the ability to magically sense the presence of a planar portal. As an action, you detect the distance and direction of the closest planar portal within 1 mile of you.

There is no ability called "Portal Lore" in XGtE, nor any other ability which detects portals, so it seems this "Detect Portal" is meant to replace it.

As for whether Detect Portal works on portals currently not open, I would refer you to the very section you mentioned in the DMG, page 45:

...most portals don't stand open all the time, but open only in particular situations or when a certain requirement is met.

Though there is no explicit language about closed portals being as "detectable" as open ones, semantically we see that a portal is still considered to be a portal even when not currently open. RAW, then, if a ranger can detect a portal, they can detect a closed portal.