Stealweb

This spell is cast on an archway, portal, doorframe, window, or other solidly defined opening-though this can be as crude as the space between two standing stones or boulders. Like a magic mouth spell, it waits, radiating only a faint dweomer until its specific trigger conditions are met, and then lashing out. (Its usual trigger condition is “when any nongood-aligned wizard passes through.”)

A bright web of glowing white force-lines appears, washes over the affected victim (a creature passing through the opening), and then vanishes. The creature suffers 4d4 points of damage from a blast of raw spell energy (save vs. spell for half damage). However, a creature affected by a steal-web is forever immune to that particular steal-web, nor does the web activate at the being's repeat passage, though its conditions are otherwise unchanged.

A stealweb activates whenever its conditions are met, and activates once per level of its caster. It is destroyed by destruction of its opening or by a successful dispel magic spell.

The caster of a stealweb cannot be harmed by her own spell, even if she meets the conditions for its activation as stated during casting.

The material components are a piece of phosphorous, a flint, and a scrap of cobweb.

The name of this spell comes from an earlier variant (now lost) from ancient Netheril that stole spells from the minds of those who activated it. The current spell is most often used to protect wizards' strongholds.