ReAct Agent (Tool Loop)
Agent decides tools and actions. Loops and failures compound.
API Calls per Conversation
Low
2
Mid
4
High
10
Best Use Cases
Tool-using assistantsWeb browsing agentsCode execution agentsDynamic research tasks
Cost Drivers
- •Unpredictable loop count (2-10+ iterations)
- •Each tool use = 2 API calls (tool request + tool result)
- •Tool definitions add ~500 tokens per tool per request
- •Failure retries compound context (18% growth per failure)
Monthly Cost Scenarios
100/day
Sonnet 4.5 (3 tools)
$360-1,200/mo
500/day
Sonnet 4.5 (5 tools)
$2,700-9,000/mo
1,000/day
Haiku 4.5 (3 tools)
$1,800-6,000/mo
Optimization Tips
- →Add loop detection — cap iterations at a reasonable maximum
- →Only include tool definitions that are relevant to the current task
- →Use structured error messages to help the agent recover without extra iterations
- →Monitor and log iteration counts to identify runaway conversations
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