ModelDiff — AI coding assistant behavior change tracker

For heavy subscribers of AI coding tools to monitor silent model behavior changes and avoid workflow interruptions

Problem

A user subscribed to GitHub Copilot's ChatGPT model ($40/mo) noticed AI behavior changes at the start of each month—e.g., an accept button appeared after writing code yesterday but vanished today. This opaque monthly model update feels strange and hurts productivity; users never know when or what changed and can only adapt passively.

Solution

An automated monitoring service: users submit a fixed set of coding prompt tasks via browser extension or CLI; the service runs them on the target AI coding tool daily/weekly, recording outputs, UI elements (e.g., whether an accept button appears), response times, and generates diff reports. Supports Slack/email notifications and retains historical snapshots for retrospective comparison.

Users

Developers paying monthly for AI coding tools, team tech leads, AI tool reviewers

MVP

Provide 5-10 preset coding task prompt templates; use Playwright to automatically run in the target AI coding tool (e.g., Copilot) and capture screenshots/DOM snapshots; compare two snapshots and output a diff report; send alerts via email or webhook; keep the last 10 snapshots.

Revenue

Subscription ($8-12/mo), team tier for multi-account monitoring; or pay per monitored task.

Why now

AI coding tools (Copilot, Cursor, Windsurf, etc.) update frequently but lack changelog transparency, and heavy users have a strong need for workflow stability; an indie dev can quickly implement with headless browser + diff—low technical barrier.