SystemDesign.ai needs two API keys. Both can be used for free.
Powers the AI judge, question generator, and interviewer chatbot.
- Go to openrouter.ai and create an account
- Go to openrouter.ai/keys → Create Key
- Copy the key (starts with
sk-or-v1-...) - Paste it into Settings → OpenRouter API Key in the app
Many models on OpenRouter are completely free. To use them:
- Go to openrouter.ai/models
- Filter by "Free" to see available models
- Copy the model ID (e.g.
meta-llama/llama-...) - Paste it into Settings → Smart Model or Fast Model in the app
No credits needed for free models. For paid models, add credits at openrouter.ai/credits — $5 lasts hundreds of sessions.
Powers audio transcription (speech → text). Free tier is generous (1,500 requests/day).
- Go to aistudio.google.com/apikey and sign in with Google
- Click Create API Key → select or create a project
- Copy the key (starts with
AIza...) - Paste it into Settings → Gemini API Key in the app
This is what I personally use. All free models — no credits needed. Swap in whatever works for you.
| Problem | Fix |
|---|---|
| Judge or chatbot errors | Check OpenRouter has credits (or use a free model) |
| Transcription fails | Check Gemini key is valid, try again in a minute (rate limit: 15 req/min) |
| No audio recorded | Enable "Audio Recording" in Settings, grant mic permissions |