The eight-corners rule is a rule applied by courts to determine whether an insurance company (insurer) has a duty to defend a claim made against its insured policyholder (insured). The eight-corners rule provides that the duty to defend is determined by comparing the “four corners” of the plaintiff’s pleading (lawsuit) with the “four corners” of the liability insurance policy.

In applying the eight-corners rule, courts generally do not consider facts or evidence from outside the four corners of each of these documents and take the plaintiff’s factual allegations in the pleading as true for purposes of determining whether the insurer has a duty to defend.

But some courts have held that outside or extrinsic evidence may be considered if it demonstrates collusion or fraud between the plaintiff and the insured for the purpose of invoking an insurer’s duty to defend.

Courts generally apply the eight-corners rule liberally and resolve any doubts in favor of the insured by finding the insurer has a duty to defend the insured against the claim(s).

In Alaska, the eight-corners rule is not explicitly codified in state statutes but is a principle that has been recognized and applied by Alaska courts. This rule dictates that an insurer's duty to defend its insured in a lawsuit is determined by comparing the allegations in the complaint (the 'four corners' of the plaintiff's pleading) with the provisions of the insurance policy (the 'four corners' of the policy). Alaska courts typically do not consider extrinsic evidence outside of these documents when applying the eight-corners rule. However, if there is evidence of fraud or collusion between the plaintiff and the insured, courts may consider such evidence in determining the duty to defend. Alaska courts generally interpret the eight-corners rule in a manner that favors the insured, meaning that if there is any doubt as to whether the allegations in the complaint potentially fall within the policy coverage, the insurer is likely to have a duty to defend the insured.