RepeatCommentBot

Inspiration

The idea came directly from a Reddit moderator from the subreddit r/selfie, who reached out with a frustrating problem their subreddit was being flooded with accounts posting the same generic comments over and over across every post. "Beautiful!" on every photo. "Great post!" on every thread. Manually catching these accounts was tedious and time-consuming, and existing tools didn't solve it. That conversation inspired RepeatCommentBot

What it does

RepeatCommentBot silently monitors every comment posted in a subreddit and tracks each user's comment history. When a user posts the same or similar comment across multiple different posts and hits the configured threshold, the mod team gets alerted automatically, either via modmail or a report to the mod queue, depending on their preference.

Everything is configurable. Mods can set how many repeat comments trigger a flag, how similar comments need to be to count, and how they want to be notified. The bot never takes action on its own, it surfaces the information and lets moderators decide.

How I built it

RepeatCommentBot is built on Reddit's Devvit platform using the new Hono-based web framework. Comment history is stored per user in Redis, and similarity is calculated using a bigram-based Dice coefficient algorithm. At 100% similarity threshold, the bot switches to exact string matching for precision. Settings are fully configurable per subreddit through Devvit's native settings system.

Challenges I faced

The biggest challenge was working with the new Hono-based Devvit framework, which had limited documentation and differed significantly from the older public API. Simple things like reading settings, calling reddit.report(), and accessing Redis required trial and error to get right. I also ran into a Rolldown memory crash on Windows that required downgrading Vite to get the build working.

What I learned

Building on Devvit taught me a lot about event-driven architecture — writing code that reacts to user actions rather than running on demand. I also learned how to design configurable tools for non-technical users, where the defaults need to make sense out of the box but the flexibility needs to be there for power users. Most importantly, I learned that the best projects come from real problems real people have.

Built With

• devvit
• hono
• node.js
• reddit
• redis
• typescript
• vite