MCP success is not correctness: builders debate who verifies side effects after tool calls
marcin_michalak · reddit · 2026-07-26
A founder building MCP-based agent hosting asks a practical question: a successful MCP tool call does not mean the underlying action was correct.
The post points out that a deploy tool can return success while shipping the wrong build, and a database tool can return success while updating the wrong rows. The real gap is not protocol success, but post-action verification.
The author wants to know what people are actually doing in practice with real side effects:
- should the client-side agent verify its own tool calls?
- should the server verify the outcome before returning success?
- or is the industry still effectively treating a 200 OK as “done”?
It is framed as a genuine implementation question for infra, deploy, and data-write tools.
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