TypeMate: Building a System-Wide Writing Assistant for Flutter on Android

Sometimes the simplest ideas solve the biggest headaches.

I wanted a way to trigger a writing assistant overlay whenever a user taps on a text field in any app. Simple to describe. Surprisingly tricky to build — especially in Flutter.

This blog is about how that problem led to TypeMate, a Flutter plugin that lets you create system-wide overlays on Android.

💡 The Problem

Most writing tools live inside one app — think Grammarly, Google Docs, Notion.
But what if you want:

Grammar check in your messaging app
AI suggestions in your email app
Quick text snippets for any form

On Android, it’s technically possible with Accessibility Service + Overlay, but Flutter didn’t have a clean solution.

🛠 The Approach

The concept:

User taps a text field in any app
        ↓
Accessibility Service detects focus
        ↓
Overlay bubble appears on top
        ↓
User interacts with writing assistant tools

📦 What TypeMate Does

TypeMate combines three components:

1. Flutter Plugin Interface

The Dart API that developers call:

await TypeMate.instance.initialize();
await TypeMate.instance.startOverlayService();

2. Android Accessibility Service

Detects when a TYPE_VIEW_FOCUSED event happens in any app.

3. Overlay Service

Shows a draggable, customizable bubble using SYSTEM_ALERT_WINDOW.

⚙️ Key Features

System-wide overlay detection
Customizable bubble UI
Runs in the background as a Foreground Service
Permission handling (Overlay + Accessibility)

🔍 The Technical Challenges

Permission Flow

Android requires manual enabling of both the Overlay & Accessibility Service.
TypeMate provides methods to open these settings easily.

2. Battery Optimisation

Foreground Service is needed to avoid the system killing it.

3. Cross-App Event Handling

Accessibility events are noisy — filtering only text field focus events was key.

🚀 Use Cases

AI Writing Assistant
Connect to GPT or other NLP tools to improve writing in real-time.
Grammar & Spell Check
Like Grammarly, but integrated into any text field.
Quick Insert Tools
Add snippets, templates, or frequently used phrases anywhere.
Custom Productivity Tools
Translate text, expand shorthand, etc.

📌 Example Usage

TypeMate.instance.textFieldFocusedStream.listen((_) {
  print("Text field focused in an external app");
  // Show your custom tools
});

🚦 Limitations

Android only (iOS blocks system-wide overlays)
Manual permission steps required
API Level 21+ needed for overlay features

💬 Closing Thoughts

TypeMate is just starting.
Planned features:

Custom bubble UI builder in Flutter
Better performance & event filtering
Integration-ready hooks for AI/NLP tools

I’d love the community to try it, break it, and improve it.

📦 Pub.dev: TypeMate
💻 GitHub: Repository

The Human Side of Code