Every MCP tool passed in isolation, yet the workflow still failed — test full chains
Stock-Pumpkin-8859 · reddit · 2026-10-05
The author shares an MCP testing lesson: Create, Fetch, and Update each passed in isolation, but running the full sequence revealed that the ID returned by the first call wasn't correctly passed to the next step — every tool worked while the workflow failed.
The takeaway: don't just ask "does this tool work?" — ask "can the agent use this tool's result correctly in the next step?", capture and validate the data handed between tool calls, and test end-to-end workflows rather than tools one at a time.
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