Not another budget cap. Curb is a real-time circuit breaker: it catches the retry-storm or fan-out loop mid-run, pauses the offending agent — not your whole API key — and texts you before the money's gone.
# your agent, 3am, stuck in a loop agent → openai/gpt-5 call #1,204 $0.02 agent → openai/gpt-5 call #1,205 $0.02 agent → openai/gpt-5 call #1,206 $0.02 ✕ BUDGET CAP HIT ($50/day) curb ⏸ agent paused · you were texted · spend frozen at $50.04 # without Curb, that loop runs till morning: $600+
You give an agent an API key and turn it loose. One retry loop, one bad prompt, one recursive tool call — and the bill runs all night with nobody watching.
An API key has no spend limit. Hand it to an autonomous agent and you're trusting it not to loop. It will loop.
The whole point of an agent is that it runs unattended. That's also exactly when a runaway bill happens.
Provider dashboards update slowly and alert late. By the time you see it, the money's already spent.
Point your agent's base URL at Curb instead of the provider. That's it — Curb meters every call and enforces the budget before the money leaves.
Change your OpenAI/Anthropic base URL to Curb's. Your keys stay yours, stored encrypted. No SDK rewrite.
Per agent, per day, per tool: hard dollar caps. Soft warnings at 50/80%, hard stop at 100%.
Hit the cap and Curb pauses the agent and texts you — spend frozen. Resume with one tap when you're ready.
We're building Curb now and onboarding early users first, free during beta. Drop your email and we'll get you in.
We'll reach out with early access soon. Want in faster? Reply to the confirmation with what you're building and we'll bump you up.
Your provider keys are stored encrypted and used only to forward your own calls. Curb is a metering + policy layer in front of the provider — it never trains on or logs your payloads.
Curb is a thin proxy — the budget check is in-memory and adds single-digit milliseconds. The provider call is the same as always.
Starting with OpenAI and Anthropic (the base-URL swap works for both), with more and an x402/agent-payment path on the roadmap.
Those give you a coarse, account-wide monthly cap — it won't save you from a spike that burns the whole day's budget in minutes, and when it trips it kills your entire key. Curb watches each agent in real time, catches the runaway loop as it happens, and pauses only the agent causing it, with per-agent cost attribution so you know exactly who's burning money.
Free during beta for waitlist members. Paid tiers later will be a small flat fee well under what one prevented runaway bill costs you.
Join the waitlist and get early access free.