reddit mod tools hackathon · proof page

dupe-detector.

A Reddit-native duplicate-review tool built entirely inside Devvit. Posters see likely repeats before they hit submit. Mods get a structured 7-day duplicates queue with similarity scores and one-click actions. No LLM. No off-platform HTTP. No fake demo.

open devpost submission ↗ open reddit app listing ↗ community proof page →
submission deadline May 27, 2026 · Reddit Mod Tools Hackathon
✓ app approved & live on reddit ✓ devpost project public ✓ 43-second walkthrough video ✓ 4 real screenshots ✓ live community feedback threads ✓ vimeo mirror of demo

01 · demo

the full walkthrough.

43 seconds covering both surfaces: poster precheck and moderator queue. Recorded against real Reddit infrastructure, not a mock or a local fixture.

direct MP4 ↗ vimeo mirror ↗ live-data proof screenshot ↗

02 · screenshots

the two workflows, in four frames.

All screenshots are from the live Reddit Developer Platform, not mocked states or local renders.

dupe-detector precheck screen — draft post compared against recent similar posts with similarity scores

poster precheck

Shows the user their likely duplicates before they submit. The tool surfaces the closest threads with a short excerpt and similarity score, not a binary block.

dupe-detector moderator queue — list of suspected duplicate posts with similarity scores and mod actions

moderator queue

Mods see the last 7 days of likely duplicate pairs, ranked by similarity. Each row has a direct link to both posts and one-click lock/remove/leave.

dupe-detector clean-state — no likely duplicates found message

clean state

When the queue is empty, the tool says so and gets out of the way. No empty skeleton, no placeholder content. Clean boards matter for mod trust.

dupe-detector live precheck rendered against real AskReddit data

live-data proof shot

Precheck rendered against real public AskReddit posts, not a controlled fixture. Confirms the similarity engine works on live Reddit content at scale.

03 · architecture

built entirely inside devvit.

The entire tool lives in the Devvit sandbox. No external HTTP, no scheduler, no LLM API, no third-party service. This is a constraint, not a simplification — it means the tool installs in seconds and never touches external infrastructure.

similarity engine

token overlap scoring

Title similarity is computed via normalized token overlap — fast, explainable, no model inference. Threshold is adjustable per subreddit by mods via a settings menu.

storage

devvit redis kv

Post metadata for the last 7 days is stored in Devvit's built-in Redis KV. No external database, no HTTP writes, no off-platform data. Keys expire automatically.

triggers

onPostSubmit hook

When a post is submitted, the Devvit hook fires the precheck synchronously against the KV store. The mod queue reads the same store on-demand when opened.

permissions

zero http permission

The app manifest does not request the http permission. Judges can verify this in the source — the tool makes no outbound network calls.

ui

devvit blocks (native)

Both surfaces — poster precheck card and moderator queue — are built with Devvit Blocks, Reddit's native UI framework. No external CSS, no iframes.

install surface

reddit developer platform

Mods install via the official Reddit Developer Platform. The app is live, approved, and publicly installable on any subreddit.

04 · hackathon alignment

against the judging criteria.

Mod Tools Hackathon prizes apps that solve a real moderation problem, use native Reddit/Devvit features, and can be proven to work. dupe-detector addresses each criterion directly.

mod problem addressed
Duplicate post cleanup is a recurring moderator tax on every high-volume subreddit. Existing tools require manual queue archaeology or off-platform scripts. dupe-detector keeps it inside Reddit and inside the mod workflow — no external tool required.
devvit native features used
Redis KV, Devvit Blocks UI, onPostSubmit trigger, native mod menu integration, subreddit settings panel. No http permission requested. All features are from the Devvit platform SDK.
originality
The similarity engine, the precheck-before-submit UX pattern, the combined poster+mod dual-surface design, and the zero-external-dependency constraint are first-party design choices specific to this app. No template was cloned; no scaffold was repurposed.
working / installable
The app is live, approved, and publicly installable at developers.reddit.com/apps/dupe-detector. Any moderator can install it in two clicks. No staging build, no test credentials, no local server.
proof of real usage
The dev subreddit r/dupe_detector_dev has live feedback threads that were open to public comment before the hackathon deadline. The live-data proof screenshot was rendered against real AskReddit posts, not a controlled fixture.
submission documentation
Devpost project is public with full description, screenshots, demo video (also on Vimeo), and the app listing URL. This proof page adds full architecture notes, judging alignment, and community thread links as supplemental context for judges.

05 · community proof

open threads before the deadline.

The dev subreddit has public feedback threads that were created before the submission was finalized — the community surface was not built retroactively for judges.

🔍

The False Positive Museum is Open

Open feedback thread where moderators can submit examples where the similarity engine was overly aggressive. The thread is pinned in r/dupe_detector_dev and was created before the submission went in.

open thread on reddit ↗
📋

App listing — Reddit Developer Platform

The official listing on Reddit's developer platform showing the app is approved, live, and installable. The listing predates the hackathon submission.

open app listing ↗
🎬

Vimeo demo mirror

A Vimeo-hosted mirror of the walkthrough video, independent of the vøiddo CDN. Provides a judge-safe playback surface that doesn't require visiting voiddo.com.

open vimeo ↗

ready to judge.

The app is live, the submission is on Devpost, the proof is here. Every claim on this page has a direct link to the underlying evidence.

open devpost submission ↗ install the app ↗ all vøiddo devpost builds →