CardFlow - Rich Mobile Kanban Card Editor for Teams Who Hate Trello Mobile

Trello forces mobile users to add cards only at the bottom and strips all text formatting — CardFlow is the companion app that lets you create richly formatted kanban cards anywhere on your board from your phone in under 10 seconds. It syncs with your existing Trello boards and adds the mobile UX that Trello should have shipped in 2018.

𝕏 Post Reddit HN

Difficulty

intermediate

What is it?

Teams running on Trello desktop have a dirty secret: nobody actually uses Trello on their phone because it's terrible. CardFlow plugs directly into the Trello API, reads your existing boards, and wraps them in a mobile-first UI with inline markdown formatting, drag-to-position card insertion, and swipe gestures. No migration, no new board system — just a better mobile layer over what you already have. The target is the estimated 15 million Trello users who primarily work on mobile but tolerate the broken experience. Revenue math: $9/month per user times 200 users equals $1,800 MRR in month 2, realistic via Trello subreddit and App Store organic. Ships fast because the Trello REST API is stable and well-documented, and the entire product is a React Native app with one Supabase table for user preferences.

Why now?

Expo SDK 51 and React Native Reanimated 3 make gesture-heavy mobile apps shippable solo in days, and Trello has not updated its mobile UX in 3 years despite thousands of App Store complaints.

▸Insert cards at any board position with a long-press gesture — not just the bottom of the list
▸Inline markdown editor for card titles and descriptions with bold, bullets, and checklist support
▸Swipe-left to archive, swipe-right to assign — one-handed task management on any screen size
▸Full Trello board sync via REST API so no migration is required and desktop changes appear instantly

Target Audience

Trello power users who work mobile-first, roughly 15 million Trello users with 30% reporting mobile frustration on App Store reviews.

Example Use Case

A freelance designer manages 4 client projects in Trello and finally adds cards and moves them mid-client-call from her iPhone without the board freezing or cards landing in the wrong column.

User Stories

▸As a Trello user, I want to insert a new card between two existing cards on my iPhone, so that I can prioritize tasks mid-meeting without reordering them afterward.
▸As a project manager, I want to add bold and bullet formatting to card descriptions on mobile, so that my team can read structured notes without opening the desktop app.
▸As a solo freelancer, I want to pay a flat monthly fee to get a better Trello mobile experience, so that I stop switching to desktop just to manage my board.

Done When

✓Card insertion: done when user long-presses between two cards and a new card input appears at that exact position, not at the bottom of the list.
✓Markdown editor: done when user types bold text with asterisks and the preview renders formatted text before saving to Trello.
✓Trello sync: done when a card created in CardFlow appears on the Trello desktop web app within 5 seconds without a manual refresh.
✓Payment: done when RevenueCat paywall appears after 14-day trial, user subscribes, and full board access is restored immediately.

Is it worth building?

$9/month times 200 users equals $1,800 MRR at month 2. $9/month times 1,000 users equals $9,000 MRR at month 6 via App Store organic.

Unit Economics

CAC: $5 via App Store organic and Reddit posts. LTV: $108 (12 months at $9/month). Payback: 1 month. Gross margin: 70% after App Store cut.

Business Model

Monthly subscription per user

Monetization Path

Free 14-day trial, then $9/month. App Store and Stripe billing.

Revenue Timeline

First dollar: week 3 via TestFlight beta upgrade. $1k MRR: month 2. $5k MRR: month 7 via App Store organic.

Estimated Monthly Cost

Supabase: $25, Vercel (API proxy): $10, RevenueCat: $0 under $2,500 MRR, Apple developer fee: $8/month amortized. Total: ~$43/month at launch.

Profit Potential

Lifestyle business at $3k–$8k MRR with App Store organic as the primary growth engine.

Scalability

High — add Asana and Linear board support, team plan at $29/month, widget for iOS home screen.

Success Metrics

Week 2: 500 beta installs. Month 1: 80 paying users. Month 3: App Store rating above 4.5 stars.

Launch & Validation Plan

Post in r/trello asking about mobile pain, collect 50 upvotes or comments as signal, then build a TestFlight beta and recruit 20 testers from that thread.

Customer Acquisition Strategy

First customer: post a screen recording of CardFlow vs Trello mobile side-by-side in r/trello and r/productivity, offer TestFlight link. Then: App Store ASO targeting 'Trello mobile', ProductHunt launch, Twitter/X short demo clips.

What's the competition?

Competition Level

Low

What's the roadmap?

Feature Roadmap

V1 (launch): Trello OAuth, mobile board view, insert-anywhere, markdown editor. V2 (month 2-3): due date pickers, member assignment, iOS widget. V3 (month 4+): Android, Asana support, team plan.

Milestone Plan

Phase 1 (Week 1-2): Trello OAuth, board fetch, column render ships. Phase 2 (Week 3): drag gestures, card editor, RevenueCat billing ships. Phase 3 (Month 2): App Store public launch with 50+ beta user reviews.

How do you build it?

Tech Stack

React Native (Expo), Trello REST API, Supabase, Stripe — build with Cursor for API integration, v0 for component inspiration adapted to React Native.

Suggested Frameworks

Expo, React Native Reanimated, Supabase JS

Time to Ship

3 weeks

Required Skills

React Native with Expo, Trello REST API, Supabase, Stripe or RevenueCat.

Resources

Trello API docs, Expo docs, RevenueCat for in-app billing, React Native Reanimated docs.

MVP Scope

app/(tabs)/board.tsx (main board view), app/(tabs)/card.tsx (card detail editor), lib/trello.ts (Trello API client), lib/db/schema.ts (user prefs table), components/KanbanColumn.tsx (column with insert gesture), components/CardEditor.tsx (markdown editor), lib/auth.ts (Trello OAuth flow), seed.ts (mock board for demo mode), .env.example (TRELLO_API_KEY, SUPABASE_URL, REVENUECAT_KEY).

Core User Journey

Install app -> sign in with Trello OAuth -> see existing boards -> insert card at any position -> pay after 14-day trial.

Architecture Pattern

User authenticates with Trello OAuth -> token stored in Supabase -> app fetches boards via Trello REST API -> React Native renders board -> card mutations POST back to Trello API -> local optimistic UI update.

Data Model

User has one TrelloToken. User has many BoardPreferences. BoardPreference stores column order overrides and display settings per Trello board ID.

Integration Points

Trello REST API for board and card data, Supabase for user preferences, RevenueCat for in-app subscriptions, Expo for mobile build and OTA updates.

V1 Scope Boundaries

V1 excludes: Android build, team sharing, Asana/Linear support, offline mode, custom automations.

Success Definition

A Trello user finds CardFlow on the App Store, installs it, connects their existing board, and pays without any founder contact.

Challenges

Trello's API rate limits at 100 requests per 10 seconds per token — batching card fetches is critical or the board will feel slow on large workspaces.

Avoid These Pitfalls

Do not build a custom board backend — always write mutations back to Trello so users never fear lock-in. Do not launch on Android before iOS is validated. Do not add Asana support until Trello is profitable.

Security Requirements

Trello OAuth tokens stored encrypted in Supabase with RLS scoped to user ID. No card content stored server-side. Rate limiting on any proxy routes at 60 req/min per user.

Infrastructure Plan

Expo EAS for mobile builds and OTA updates, Supabase for Postgres, Vercel for any API proxy routes, Sentry for crash reporting — estimated $43/month.

Performance Targets

Board load from Trello API under 1.5s for boards with up to 200 cards. Card mutation optimistic update under 100ms. App cold start under 2s on iPhone 12.

Go-Live Checklist

☐Security audit complete.
☐RevenueCat payment flow tested.
☐Sentry crash tracking live.
☐Trello OAuth tested on iOS 16+.
☐App Store listing with screenshots ready.
☐Privacy policy and terms published.
☐20 TestFlight beta users signed off.
☐Rollback plan for hotfix via Expo OTA documented.
☐Reddit and ProductHunt launch posts drafted.

First Run Experience

On first run: a demo mode loads a pre-seeded mock board called 'My Projects' with 3 columns and 8 cards so the user sees the UI immediately. User can immediately drag cards and test the markdown editor without connecting Trello. No manual config required: Trello OAuth is optional for the first 5 minutes of demo exploration.

How to build it, step by step

1. Define Supabase schema for user tokens and board preferences in schema.ts. 2. Run npx create-expo-app with TypeScript template. 3. Implement Trello OAuth flow in lib/auth.ts using Expo AuthSession. 4. Build Trello REST client in lib/trello.ts with rate-limit-aware batching. 5. Build KanbanColumn.tsx with React Native Reanimated drag gestures and insert-at-position logic. 6. Build CardEditor.tsx with markdown input and preview toggle. 7. Wire RevenueCat paywall to the 14-day trial expiry check on app open. 8. Add demo mode in seed.ts that loads a mock board without Trello auth for App Store screenshots. 9. Submit TestFlight build and recruit 20 beta testers from r/trello. 10. Verify: connect a real Trello board, insert a card mid-list, edit with markdown, confirm change appears on Trello desktop within 3 seconds.

Generated

April 25, 2026

Model

claude-sonnet-4-6

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Disclaimer: Ideas on this site are AI-generated and may contain inaccuracies. Revenue estimates, market demand figures, and financial projections are illustrative assumptions only — not financial advice. Do your own research before making any business or investment decisions. Technology availability, pricing, and market conditions change rapidly; always verify details independently.