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 Florida, the eight-corners rule is utilized to determine if an insurer has a duty to defend its insured in a lawsuit. This rule involves a comparison of the complaint's allegations (the 'four corners' of the plaintiff's pleading) with the terms of the insurance policy (the 'four corners' of the policy). Florida courts adhere to this rule by focusing on the allegations in the complaint and the language of the policy without considering external evidence. However, if there is evidence of fraud or collusion between the plaintiff and the insured, courts may allow extrinsic evidence to assess the duty to defend. Florida courts are inclined to interpret the eight-corners rule in a manner that favors the insured, often resolving ambiguities in the insurance policy to find that the insurer has a duty to defend the insured against the claims.