Your Free AI Tier Is Shared. Build the Gate.

This week, DEV is arguing about who reviews AI output ( discussion ). The community keeps asking the same question. My answer is different. Review the boundary first, not the output. The output is visible. The boundary is not. That is where the risk hides. Agents get the memory debates. The gateway gets none. A free AI tier is a shared service. It has a budget, a concurrency ceiling, and no SLA. Treat it that way. Put a gateway between your app and the model. The gateway owns the budget, the queue, and the breaker. MonkeyCode is an open source project. It offers free model access and a free server option. The free tier gives you a 10M token monthly budget. That number is a constraint, not a feature. Design around it before you build on it. Disclosure: This article was prepared as part of MonkeyCode's product outreach. Think of the free tier as a water pipe. The pipe has a fixed diameter and a monthly meter. Your app is a set of open taps. Without a valve, the meter empties fast and the pipe floods. The gateway is the valve. Direct calls look simpler. They are simpler for one request. They fail at the tenth. The gateway absorbs the variance. Your app never sees a 429. Your app never sees an empty budget. Constraints Three constraints define the design. First, the 10M token budget is monthly. It does not reset daily. It does not roll over. Second, the free server serializes work. Concurrency of one is a safe assumption. Third, there is no SLA. The endpoint can stall, throttle, or return 429 at any moment. These constraints are not bugs. They are the contract. A good architecture reads the contract. Then it shapes the data flow around it. Data flow The flow has six stages. The client sends a prompt to the gateway. The gateway checks the token budget. It enqueues the request. A single worker drains the queue. The worker calls the model endpoint. The response returns to the client. Add two escape paths. When the budget is empty, the gateway returns a fallback answer. Whe