x402 Agent Spending Guard: Give Your Agent a Budget Before You Give It a Wallet

x402 Agent Spending Guard is a free, open-source npm package that prevents x402 payments from exceeding a set budget. The package provides budget cap, per-payment cap, emergency stop, and optional Pay Safe verdict (GO/CAUTION/STOP). The package was released on September 30, 2026, and is available in both JavaScript and Python versions.

The package was developed due to the failure of 2,777 out of 27,499 endpoints to pass their last health check on September 30, 2026, and the fact that 1,495 endpoints charged more than their own directory listing. The package was released as a response to the ecosystem's need for a solution to prevent such failures.

The guard enforces the budget cap and per-payment cap, with an optional Pay Safe verdict of GO, CAUTION, or STOP. The decision gate decides whether the payment should be made based on a confidence score ranging from 0 to 1. If the score is 0.80 or higher, the payment is auto-paid. If the score is between 0.50 and 0.79, the payment is sent for confirmation. If the score is below 0.50, the payment is blocked, logged, or escalated.

The guard works by setting a ceiling before funding, adding a confirm band, performing a pre-payment verdict, and deciding on the instruction. The guard speaks the decision gate, ensuring that the wallet only signs payments that have been approved by the guard. The decision gate uses a simple but effective mental model that answers the question 'can we afford it' with fail-closed rules.