AI/LLM • Mobile App • 0→1

ToneCheck shipped an AI-powered grammar and tone checker for iOS

HyperNest Labs built ToneCheck from concept to App Store—an AI tool that checks grammar, spelling, and tone without rewriting your voice.

10 weeks

Build time

iOS

Platform

3

AI features

Freemium

Pricing

Build your AI mobile app

Client snapshot

Company
ToneCheck
Industry
Productivity / AI
Stage
0→1
Headquarters
Remote

Timeline

  1. Week 1-2

    Product design, AI model selection, and iOS architecture.

  2. Week 3-5

    Core grammar and spelling check with AI tone analysis.

  3. Week 6-8

    Custom iOS keyboard, auto-fix suggestions, and app integrations.

  4. Week 9-10

    Pro subscription setup, App Store optimization, and launch.

Problem → Action → Outcome

A quick operator-level summary of what changed.

Problem

Grammar tools rewrite messages into robotic corporate-speak, losing the user's authentic voice.

Action

HyperNest built an AI-powered iOS app with custom keyboard that flags grammar, spelling, and tone issues without rewriting—preserving the user's voice.

Outcome

ToneCheck launched on the App Store in 10 weeks with freemium pricing, privacy-first design, and a unique 'fix without rewriting' approach.

The challenge

The founder was frustrated with grammar tools that rewrite messages into corporate-speak. They wanted a tool that catches real issues while preserving the user's authentic voice.

  • Build AI that flags issues without rewriting the entire message
  • Create a custom iOS keyboard for in-app checking
  • Ensure privacy—messages should never be stored or used for training
  • Design a freemium model with clear value progression

What we built

Our team built ToneCheck combining AI for tone analysis with traditional NLP for grammar and spelling, wrapped in a beautiful iOS app with a custom keyboard.

GPT-powered tone analysis with confidence scoring
Grammar and spelling check using hybrid AI/NLP approach
Custom iOS keyboard extension for checking in any app
Privacy-first design with no message storage
StoreKit 2 integration for subscription management

Impact

ToneCheck launched on the App Store offering a unique value proposition: grammar checking that doesn't change who you are.

Shipped iOS app with custom keyboard in 10 weeks
Three AI features: grammar, spelling, and tone analysis
Free tier with 15 checks/day, Pro at $5/month for 200/day
Zero message storage for complete privacy

Stack & capabilities

Tools, platforms, and competencies we owned for this engagement.

Mobile

  • Swift
  • SwiftUI
  • Keyboard Extension

AI/ML

  • OpenAI GPT-4
  • Custom NLP
  • LanguageTool

Backend

  • Node.js
  • Vercel Edge Functions

HyperNest built exactly what I envisioned—an AI grammar tool that helps without overstepping. The custom keyboard works flawlessly across all my apps.

ToneCheck Founder

Founder

Need these outcomes for your startup?

We'll replicate the playbook and customize it to your goals.

How this applies to other startups

  • AI product builders can apply the same 'assist without overriding' design philosophy.
  • iOS developers can learn from our custom keyboard extension implementation.
  • Founders building freemium AI apps can replicate this pricing and feature strategy.