The two Democratic candidates for attorney general, Maura Healey and Warren Tolman, have agreed to a so-called "people's pledge" to discourage campaign ads funded by outside groups.
Under the agreement, each candidate has agreed to pay 100 percent of the cost of any ad launched by an outside group to The One Fund if that ad either supports their candidacy or attacks their opponent. The One Fund support Marathon bombing victims.
The deal applies to television, cable, satellite and radio ads as well as online advertising and direct or bulk mail advertising.
The deal is designed to ensure the candidates are directly responsible for their ads.
The agreement is a stricter version of the "people's pledge" signed by Republican incumbent Scott Brown and Democratic challenger Elizabeth Warren during Massachusetts' 2012 Senate race.