BridgingBot

BridgingBot is an LLM-powered moderator prototype designed not to remove content but to model the behavior of a human mediator inside an online thread. The bot is the work of Jeff Fossett, Research Lead at the Plurality Institute and a recent Harvard PhD whose work covers collective decisions about emerging digital technologies. The project ran with collaborators at Harvard, UC Berkeley, Jigsaw, and Google.org, and was supported by the Plurality Institute starting in early 2025.

Behaviorally, BridgingBot steps into a thread, paraphrases the positions present, reframes them in terms of underlying needs, and surfaces common ground. The Plurality Institute's writeup gives a concrete example: in r/Boston on Reddit, in a thread arguing about a delivery truck parked in a bike lane, BridgingBot posted an intervention that paraphrased the dispute as a tradeoff between the driver's work constraints and bike-lane safety and legality, then asked whether better city infrastructure could reduce the tradeoff. This is the de-escalation-by-translation pattern that distinguishes the bot from classifier-based moderation that suppresses content.

The project has two methodological features uncommon in production moderation tooling. The first is a randomized controlled trial of the bot in deployment, which is the appropriate empirical standard for a civic-tech intervention but is rarely used by commercial platforms. The second is a commitment to open-source the code and methodology in full. The bot also sits alongside a parallel academic line on bots that broaden the range of arguments in online discussions, including the ArgumentBot study from the University of Zurich (Vuk, Sarasua, Gilardi, June 2025), which found that an LLM bot that surfaces missing arguments measurably widened the spread of perspectives even when transparently disclosed as AI.

The grant sits in the agents and governance meta-layers. BridgingBot is the canonical example in the Plurality Institute's broader thesis that LLMs can serve as civic infrastructure for deliberation rather than as outrage amplifiers.