Hidden Cost Black Holes in MCP Tool Calls
C00LDude6ix9ine · reddit · 2026-07-15
While troubleshooting cost overruns across multiple agent systems, the author discovered that calculating costs per entire run reveals almost no waste; the real focus should be on the cost of individual MCP tool calls.
The post lists several common issues:
- The same tool being called repeatedly, often due to a lack of session-level caching
- Retrieval / memory looking like a "memory cost" when it actually includes massive embedding and retrieval overhead never used by the final answer
- Tool schemas and long descriptions being repeatedly counted as input tokens on every call
- Many observability dashboards only showing total agent costs, making it impossible to pinpoint "which tool is burning money"
The author offers a rough calculation: if a single tool call costs $0.003 and runs an extra 10,000 times daily, that one tool could add roughly $900 in monthly expenses.
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