RuneScape Classic Wiki
RuneScape Classic Wiki
The main RuneScape Wiki has an article on: Poisoned Rune Throwing Dart
The Old School RuneScape Wiki also has an article on Poisoned Rune Throwing Dart.

A Poisoned Rune Throwing Dart is a poisonous throwing dart. It is the strongest poisonous throwing dart in RuneScape Classic, and is made by adding weapon poison to a rune throwing dart. It has no requirements to equip, which may be a glitch, as the non-poisoned version requires 35 Ranged to equip.

Like all throwing darts, they provide no WeaponAim or WeaponPower, and when they are equipped, they are invisible to other players. However, they provide a significant invisible ranged bonus.