PostCipher

A daily cryptogram-style puzzle based on popular and trending Reddit posts with a practice mode that lets users select preferred subreddit from which the app captures posts for practice puzzle content

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PostCipher: Daily Cryptograms from Reddit's Best

Inspiration

Word games thrive on Reddit—from crossword communities to daily puzzle threads. But existing daily games felt disconnected from what makes Reddit special: the incredible variety of voices, ideas, and moments that bubble up through the platform every day.

We wanted to create a daily game that feels native to Reddit—one that doesn't just live on the platform, but is made from the platform itself. What if each day's puzzle could be a window into Reddit's collective memory? A trending post from today, a viral moment from years ago, or a gem from a niche community you've never discovered?

PostCipher turns Reddit's own posts into cryptogram puzzles, creating a daily ritual that celebrates the platform's best content while challenging your code-breaking skills.

What It Does

Every day, PostCipher presents players with an encrypted Reddit post title or comment. Using classic substitution cipher logic, players decode the message letter by letter. The puzzle is the same for everyone that day—fostering shared experience and community discussion.

Core mechanics:

  • Daily puzzle format - One puzzle per day, same for all players
  • Hint system - Strategic reveals when you're stuck (with scoring impact)
  • Time & accuracy scoring - Compete on both speed and efficiency
  • Shareable results - Post your score without spoiling the puzzle (Wordle-style)
  • Source reveal - Solved puzzles link back to the original Reddit post

The content library draws from Reddit's archive, surfacing memorable posts while filtering for appropriate length and quality. Each solved puzzle becomes a small moment of Reddit archaeology.

How We Built It

Technology Stack:

  • Reddit Developer Platform & Custom Post API
  • React for UI components
  • Vanilla JavaScript for cryptogram engine
  • Reddit API for content sourcing and score sharing

Architecture: We built PostCipher as a Reddit Custom Post, ensuring it works seamlessly in both mobile and web experiences. The core challenge was balancing complexity (engaging puzzles) with mobile-first accessibility (playable in short sessions).

Development approach:

  1. Prototype phase - Built standalone web version to validate game mechanics and difficulty balancing
  2. Reddit integration - Migrated to Custom Post framework, adapting for platform constraints
  3. Content pipeline - Developed filtering system for selecting appropriate Reddit posts
  4. Polish & testing - Refined UX for Reddit's webview environment

Challenges We Faced

Content curation at scale: Reddit produces millions of posts daily. Building filters to identify puzzle-worthy content—interesting enough to solve, appropriate for all audiences, right length for mobile—required careful tuning. We developed heuristics around character count, word diversity, and source subreddit reputation.

Mobile-first cryptogram UX: Traditional cryptograms assume keyboard input and large screens. Designing an intuitive touch interface for letter substitution on mobile devices required multiple iterations. Our final solution uses a streamlined letter-selection system optimized for thumbs.

Daily puzzle distribution: Ensuring every player gets the same puzzle each day while preventing spoilers required thoughtful state management. We implemented server-side puzzle generation with client-side validation to prevent tampering.

Reddit platform constraints: Custom Posts have specific technical limitations around asset sizes, allowed libraries, and state persistence. We had to optimize our JavaScript bundle and work within Reddit's storage APIs rather than external databases.

What We Learned

Reddit as a content ecosystem: Building with Reddit's actual posts as raw material gave us deep appreciation for the platform's content diversity and community voice. The best puzzles aren't just word games—they're artifacts of Reddit culture.

Daily game psychology: We studied what makes Wordle, Connections, and other daily games sticky. The key isn't just gameplay—it's the ritual, the shared experience, and the low-stakes competition with friends. PostCipher aims to create that same "did you get today's puzzle?" dynamic.

Mobile interaction design: Touch interfaces demand different thinking than desktop. Every extra tap matters. We learned to ruthlessly simplify interactions and provide immediate visual feedback for every action.

What's Next

Themed puzzle modes: "On This Day" historical posts, subreddit-specific challenges, or community-voted content

Enhanced social features: Friend leaderboards, streak tracking, daily discussion threads

Accessibility improvements: Colorblind-friendly themes, screen reader optimization, adjustable difficulty

Content variety: Expanding beyond post titles to include memorable comments, AMAs, and viral moments

PostCipher proves that Reddit's best content can be more than just consumed—it can be played with, puzzled over, and celebrated daily.

Built With

  • client-server-architecture
  • component-based-ui
  • concurrently
  • css
  • custom-react-hooks
  • devvit
  • devvit-reddit-api
  • eslint
  • exponential-scoring
  • express.js
  • github
  • html5
  • http-fetch
  • javascript
  • mulberry32-prng
  • node.js
  • npm
  • prettier
  • react
  • react-dom
  • reddit-public-json-api
  • redis
  • restful-api
  • serverless-functions
  • service-layer-pattern
  • string-hashing
  • substitution-cipher
  • tailwind
  • typescript
  • vite
  • vitest
  • windows
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