Terraria (Wiki): Ruler

The Ruler is a melee weapon that pierces enemies.

The Ruler is the only shortsword in the game that automatically swings. This gives it the highest DPS of any shortsword, along with its quick use rate and gold-equivalent damage. Despite this, the Goblin Tinkerer is still largely ineffective because the player will almost always have much better weapons by the time it is available (desktop, mobile, console). 

The "Ruler On" / "Ruler Off" button in the inventory's upper left corner turns on or off the display of measurement lines for block counting (desktop, mobile, console).

The Ruler is a tool for information that helps with precise block placement (old-gen consoles). 

It shows a grid structure resembling that of the Mechanical Ruler (desktop, mobile, console).

The Ruler can be reforged to have any of the typical accessory modifiers (like informational accessories), even though its primary function is referential (old-gen consoles). A Ruler cannot autoswing. Its attack reaches two tiles in radius. At an optimal distance, the Ruler can pierce two enemies. However, multiple bodies will be damaged should they all line up for the player.

When normally used, the Ruler will not emit light, and attacks do not go through walls. It has the weakest knockback, making it ineffective against waves of enemies. It swings in bursts of four, so even if the player decides to stop attacking, it will keep swinging until the burst is finished. The Ruler cannot be swung once, and any attempt to do so will result in four swings (desktop, mobile, console).

Combat-wise, the Ruler’s decent damage might be effective against a one-on-one opponent at the early stages of the game. All Flask items will imbue their unique effects since the Ruler is a melee weapon.

The Ruler sells for one-third of its original purchase price as opposed to the majority of items, which sell for one-fifth (old-gen consoles).

The Ruler is best modified with Legendary for overall stats improvement.