Symptom
When an MCP server tool raises an error, the agent gets back [{}, {}, {}, ...] instead of the error message.
Evidence what you'll see
- The tool result is a long list of {} entries
- The real exception text never reaches the agent or the user
- Only happens when the MCP tool call fails
Cause
The workbench turned the exception into a plain string, and the MCP adapter then tried to serialize that string item by item, producing one empty object per character.
Fix steps
0 of 1 done
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Verify the fix worked
- Make an MCP tool fail on purpose and confirm the agent receives the actual error text.
Sources and credit
Summarized in our own words from these public reports. Credit goes to their authors.
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