No subscription. You pay for what you use with credits, and the price of every action shows before you spend. Most of what you do while learning is free.
| Action | Credits | Why it costs |
|---|---|---|
| Place a component | 3–12 | Each component has a catalog price; see every price. |
| Copilot change | 1 | A setting, a failure, an attack or a traffic change made by typing. |
| Run above 5,000 req/s | 1 per 5,000 req/s | Bigger traffic, attacks included, takes more computing to simulate. |
| Stress test | 5 | About ten runs of rising traffic plus an attack drill. |
| AI answer | 3 | A question answered by Claude about your run. |
| AI review | 20 | A full review of a finished run, every number checked against it. |
If an AI answer or review fails, its credits are released and nothing is charged.
Change the numbers to match how you practise.
404 credits a month
About 19 credits per problem, or about $5 at the $10 pack price.
That fits inside the 25 free credits a day a guest gets (about 750 a month).
| Pack | Price | Per 1,000 credits |
|---|---|---|
| 1,000 credits | $10 | $10.00 |
| 2,750 credits (+10%) | $25 | $9.09 |
| 6,000 credits (+20%) | $50 | $8.33 |
Purchased credits never expire. Unused purchased credits are refundable within 14 days: see refunds.
Packs open soon. Leave your email and we will tell you when they do.
Teaching a distributed systems course or training a team? Ask about bulk credits through the contact form.