Case study 08
DETGate
DETGate is a planned companion to Ielzy for the Duolingo English Test. The DET is short, adaptive and taken at home, with many small question types instead of four long papers, so practice has to be quick, varied and timed. DETGate will let candidates drill each question type, take full timed mock tests, review their mistakes and follow a study plan, reusing the practice, mock-test and content foundations built for Ielzy.
No public site or source code. The architecture and the decisions behind it are described below.
- Founder & sole engineer
- Own product
- EdTech, AI
- Duolingo English Test, Exam Preparation, Mock Tests, Study Planning
- Next.js
- React
- TypeScript
- Better Auth
- Drizzle
- Neon Postgres
- Cloudflare R2
- Resend
What DETGate does
- Practice for each DET question type, from reading and listening to writing and speaking tasks
- Full timed mock tests that follow the real test's pace
- Speaking and writing practice with recorded and typed answers
- Mistake review and progress tracking by question type
- A personal study plan
- An admin content library for questions, audio and images
The problem
The Duolingo English Test is short and adaptive, with many small question types that come quickly one after another. Candidates need practice that matches that pace, not long papers designed for other exams.
Approach
DETGate will follow the loop that works in Ielzy, practise, review mistakes, track progress, but organised by DET question type, with timed mocks that mirror the test's pace. The stack and the content system carry over from Ielzy, so the work goes into the DET-specific parts.
Key decisions
- D1
Build on Ielzy
Auth, the content library, media storage and the mock-test engine are reused rather than rebuilt.
- D2
Question types first
Practice is organised around the DET's many short question types rather than four long sections.
- D3
Pace as a feature
Timers and quick transitions are part of practice, because speed is part of the test.
My contributions
- Defining the product as the Duolingo English Test counterpart to Ielzy
- Planning to reuse Ielzy's stack and its practice, mock-test and content foundations