How to Prevent AI Agent Overspending
Overspending isn't the model's fault — it's the absence of a gate between the agent and the money. The prevention is a small set of rules, deterministically enforced.
Step 1 — Cap every transaction
A per-transaction cap blocks any single purchase above a ceiling. This alone stops the largest runaway shapes.
Step 2 — Kill the loops
A velocity limit caps transactions per window. The documented runaway pattern — a retry loop — dies at the limit.
Step 3 — Control the vendors
A merchant allowlist makes unknown vendors BLOCKED by default. Procurement regains control of who agents pay.
Step 4 — Add a human gate
An approval threshold FLAGS material purchases for review — agents stay fast, big spends wait for a human.
Step 5 — Watch the log
The audit log records every decision with the rule that fired. Review it weekly; tune rules with data.
At a glance
| Rule | Stops |
|---|---|
| Per-transaction cap | Single oversized purchases |
| Velocity limit | Retry loops |
| Merchant allowlist | Unknown vendors |
| Approval threshold | Unreviewed material spend |
FAQ
Which rule is most important?
The velocity limit — it stops the most common runaway shape (retry loops) in seconds.
Do I need all four?
Three cover most risk: a cap, an allowlist, and a velocity limit. Approval adds the human gate.
Related
Stop the next $12,400 night.
One API call (or MCP tool) in front of every agent transaction — APPROVED, BLOCKED, or FLAGGED, deterministic, ~5 ms, fully logged.
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