Fact‐checking has become an important feature of the modern media landscape. However, it is unclear what the most effective format of fact‐checks is. Some have argued that simple retractions that repeat a false claim and tag it as false may backfire because they boost the claim’s familiarity. More detailed refutations may provide a more promising approach, but may not be feasible under the severe space constraints associated with social‐media communication. In two experiments, we tested whether (1) simple ‘false‐tag’ retractions can indeed be ineffective or harmful; and (2) short‐format (140‐character) refutations are more effective than simple retractions. Regarding (1), simple retractions reduced belief in false claims, and we found no evidence for a familiarity‐driven backfire effect. Regarding (2), short‐format refutations were found to be more effective than simple retractions after a 1‐week delay but not a one‐day delay. At both delays, however, they were associated with reduced misinformation‐congruent reasoning.