The Token Budget Pattern: How to Stop AI Agent Overspending Before It Starts

AI agents are expensive to run when you let them operate without boundaries. But token cost isn't random — it's a design choice. The token budget pattern gives every agent a hard cap: a maximum number of tokens per task, per session, or per day. When an agent approaches its limit, it summarizes, escalates, or stops. It doesn't just keep going. Why This Matters Without a token budget: A single runaway loop can burn 100x your expected cost Long-running tasks accumulate context until they're slow and expensive You discover the problem on your billing statement, not in your logs The Three-Level Budget Task budget: "This task should not exceed X input + Y output tokens." Session budget: "This agent session runs for at most Z tokens total." Daily budget: "This agent burns no more than N tokens per day. Write to alert.json if approaching limit." Build all three into your SOUL.md. The daily budget is your safety net. SOUL.md Template TOKEN BUDGET: - Per task: 8,000 tokens (input + output) - Pe