Sandboxer
What happens when you start more sandboxes than your plan allows?
On a paid Sandboxer plan, a start limit isn't a wall. Starts above a per-minute, per-hour or per-day limit keep working up to three times the limit, and each one is paid from your prepaid credit: $0.03 above 1x up to 1.5x, $0.05 above 1.5x up to 2x, and $0.07 above 2x up to 3x. With no prepaid credit and auto-refill off, starts simply stop at the limit.
Updated November 12, 2026
What counts as a start?
Creating, resuming and forking a sandbox each count as one start. Starts are limited per rolling minute, hour and day, and the numbers depend on your plan. Separately, your plan caps how many sandboxes can be active at once; stopped sandboxes don't count toward that. Per Sandboxer's limits docs:
| Plan | Active at once | Starts per minute / hour / day |
|---|---|---|
| $20 / month | 100 | 12 / 60 / 200 |
| $100 / month | 300 | 30 / 210 / 840 |
| $500 / month | 1,000 | 65 / 420 / 1,680 |
| $2,000 / month | 2,000 | 90 / 600 / 2,400 |
A request sent with fail-fast that is refused because no machine is ready doesn't count as a start.
How much does a start above the limit cost?
It depends on how far past the limit it falls. These are the prices on Sandboxer's pricing page:
| Start, against the limit | Price per start |
|---|---|
| Up to 1x | Free |
| Above 1x, up to 1.5x | $0.03 |
| Above 1.5x, up to 2x | $0.05 |
| Above 2x, up to 3x | $0.07 |
The same brackets apply to the minute, hour and day limits, and a start that's over in several windows pays the highest price among them. Sandboxer's own example: on the $20 plan, with 200 starts a day, 300 starts in one day cost $3 and 600 cost $22. Start 601 is refused.
Where does the money come from?
From your prepaid credit, the $20 time packs, never from your plan's included machine time. If auto-refill is on, it buys a pack when the credit can't pay for the next paid start. Paid starts need a paid plan and its first payment; complimentary plans, trials that had already started, and accounts with only time packs and no plan don't burst. See Sandboxer pricing.
How do you make sure you never pay for starts?
Keep your prepaid credit empty and auto-refill off. Starts then stop at the limit, as before: the minute and hour windows answer 429 rate_limited and the day window 429 daily_limit_reached, each with a Retry-After header, so a well-behaved orchestrator waits and tries again. For other spending limits, see how to stop an AI agent from overspending.
How can an agent see where it stands?
sbx limits --json, or GET /api/v1/limits, shows whether paid starts are available right now and why not if they aren't, what the next start would cost (0 inside every limit, null when it would be refused), and your ceilings with paid starts, each limit times three. An agent that fans out many sandboxes can check this before a burst instead of finding out from a refusal. See agent swarms and agent evaluations.
Frequently asked questions
Is there a hard ceiling on starts?
Yes: three times each limit. Past that, starts are refused until the window rolls over.
Do paid starts use my plan's included time?
No. They come out of prepaid credit (time packs) only.
Can I turn paid starts off?
Yes. Keep prepaid credit empty and auto-refill off, and starts stop at the limit.
Does a resume or a fork count as a start?
Yes. Creates, resumes and forks each count as one start.