What a spend firewall won't do
The honest limits: it won't stop every bad decision, it can't reverse settlements, and it's not a compliance certification. Here's what it actually is.
Most writing about spend firewalls sells the upside. Here's the other side — because a control you misunderstand is a control you'll mis-deploy.
It won't stop every bad decision
A firewall enforces the rules you wrote. If the rules are wrong — a cap too high, a vendor mistakenly allowlisted, a category ungoverned — the firewall will faithfully enforce the wrong policy. Rule tuning is part of the product, not an afterthought.
It can't reverse settlements
Decisions happen before the money moves. If a transaction is approved and settles, no firewall is un-ringing that bell. That's why the design favors flag-over-block for edge cases: review before settlement, not after.
It's not a compliance certification
The audit log is evidence — a control and a source of truth. It is not SOC 2, ISO 27001, or a regulatory sign-off. Pair it with your org's governance framework.
What it actually is
A deterministic decision layer on the money path: APPROVED, BLOCKED, or FLAGGED before settlement, every decision logged. That's a narrow, honest job — and it's the one control that would have stopped the documented runaways in the incident database.