The interview prep tool that doesn't want your subscription.
Walk through real system design and LLD interview problems stage-by-stage, with an AI tutor that pushes back like a senior engineer. Plug in your own AI key — pay cents, not $40/month.
Why DesignDojo
OpenAI, Anthropic, Gemini, OpenRouter, Groq. Your key. Your cost. Your control.
Point at Ollama or LM Studio. Practice never leaves your laptop.
Stage-by-stage delivery — exactly how senior engineers structure their answers.
Three steps to your next session
No account, no email, no waiting list.
- Step 01
Pick a problem
Browse the HLD or LLD library. Start with a classic — Bitly, Twitter, parking lot — or pick a Hard you've been avoiding.
- Step 02
Plug in your AI key
Paste an OpenAI / Anthropic / Gemini key, or point at a local Ollama. Stored only on this device.
- Step 03
Practice stage-by-stage
Requirements → estimation → API → data → diagrams → deep dives. The tutor grades each stage against a senior rubric.
Real questions FAANG actually asks
36 interview-ready problems and growing.
Roughly $0.0001 per session
DesignDojo itself is free. The only cost is whatever you'd pay your AI provider for ~5K tokens per stage.
- Unlimited sessions
- All problems, all stages
- Article write-ups + AI tutor
- Pay per token, not per month
- Most providers have free tiers
- Works on phone, laptop, server
- 100% offline
- Your data never leaves the laptop
- Use any open-weights model
Stop paying for interview prep.
Pick a problem, plug in a key, and walk in confident.