Is melee attacks' reach always written?

Question

So, a group of mine made this doubt pop up: do huge creatures have reach just because of their size?

From what I understand, a creature has reach on a melee attack only if it's written as this one (an adult red dragon used as an example)

jaws +29 / +24 / +19 (fire, magical, reach 15 feet)

The dragon is huge and has a different reach on every melee attack.

So a greater nightmare - although huge - should not have reach on an attack written like this, right?

jaws +24 / +19 / +14 (evil, magical)

Again, to summarize: is melee attacks' reach always written in the creature's stat block?

Edit: the first answers both seem valid, but they diverge. Any official quote would be helpful, thanks.

Answer 1

Reach Should Always Be Listed

Operative word here being "should" - I've not yet seen a creature where it seems like it was a mistake it wasn't.

The rules for reach as it corresponds to size say this:

Table 9–1 also lists the typical reach for creatures of each size...

Table 9-1: Size and Reach

Size	Space	Reach (Tall)	Reach (Long)
Tiny	Less than 5 feet	0 feet	0 feet
Small	5 feet	5 feet	5 feet
Medium	5 feet	5 feet	5 feet
Large	10 feet	10 feet	5 feet
Huge	15 feet	15 feet	10 feet
Gargantuan	20 feet or more	20 feet	15 feet

The table shows the typical reach of a Huge (Long) creature like the Greater Nightmare is 10 feet. However... note the word typical means that this is more of an FYI of what to expect than an actual rule. These rules in turn reference the Range and Reach rules on page 455 of the CRB:

Your reach is typically 5 feet, but weapons with the reach trait can extend this. Larger creatures can have greater reach; for instance, an ogre has a 10-foot reach.

Again, none of the language here implies that it's all Large or larger creatures have reach! Importantly, the referenced Ogre explicitly calls out Reach in its stat block. This would be totally unnecessary if we were to assume the typical Reach.

RAW, Reach is never assumed to be anything but 5 feet, and thus must be explicitly printed on a stat block. Thus you should assume no printed Reach means 5 feet, even for Huge or larger creatures.

This is further reinforced by the text of the Enlarge spell:

Bolstered by magical power, the target grows to size Large. Its equipment grows with it but returns to natural size if removed. The creature is clumsy 1. Its reach increases by 5 feet (or by 10 feet if it started out Tiny), and

A PC with this spell is presumably now a Large (Tall) creature. Should the above table apply to all creatures regardless, then you'd already have a 10 foot reach just for being Large! This would mean Enlarge gives you a 15 foot reach - which I suppose isn't out of the question, but it very clearly seems to be designed to keep PCs on pace with the typical reach of Tall creatures of various sizes. Again, if the typical reach from the table was to be assumed, this text would be unnecessary.

It seems reasonable to say that, RAI, it's left up to the GM to determine whether it makes more sense for the creature that doesn't mention Reach to have the default Reach or the typical Reach - there's a lot that goes into designing a creature, and it's easy for authors to miss small details, especially if they were assumed in other editions.

Answer 2

Creatures have default reach by size

This is covered in the rules for size, space and reach, core rulebook page 473:

Creatures and objects of different sizes occupy different amounts of space. The sizes and the spaces they each take up on a grid are listed in Table 9–1: Size and Reach (page 474). Table 9–1 also lists the typical reach for creatures of each size, for both tall creatures (most bipeds) and long creatures (most quadrupeds). See page 455 for more about reach. (...)
Table 9-1: Size and Reach

Size	Space	Reach (Tall)	Reach (Long)
Tiny	Less than 5 feet	0 feet	0 feet
Small	5 feet	5 feet	5 feet
Medium	5 feet	5 feet	5 feet
Large	10 feet	10 feet	5 feet
Huge	15 feet	15 feet	10 feet
Gargantuan	20 feet or more	20 feet	15 feet

So yes, Huge creatures do have reach just because of their size.

Note that this is given as the typical reach. If a creature has different reach stated, it will override these measurements, as specific rules beat general ones. For example, a dragon is not tall, so as a huge creature it would normally have 10 feet reach, but the dragon, with its long neck has 15. A huge creature like the Greater Nightmare would need to say 5 feet, if it wanted to limit you to just that short reach.

If no reach is given at all, you should assume the default reach as provided in the table, because the rules tell you so.

There is no rule (that I am aware of), that states unlisted reach is always 5 feet. The statement under Range and Reach (p. 455 core rules) that says

Your reach is typically 5 feet, but weapons with the reach trait can extend this. Larger creatures can have greater reach;

also uses the term typically and seems to be targeted towards the player characters, who are addressed with you and normally have only 5 feet of range unless their weapons change that, but the default reach of monsters is covered by the table listed above. I do however agree that it would be much more convenient if the rules listed the actual reach right there in the stat block for all monsters.