Claude debugging case: Agent failed silently due to missing parameter, framing mattered more than model
What happened
A developer used Claude to build a calendar agent. The agent was supposed to create calendar events with attendees, but when test scenarios tried to invite someone to a meeting, it created the event, reported success, but silently dropped the invite without mentioning the failure.
The debugging process
When the developer asked Claude to fix the agent through prompting (constraining the approach to not rewriting tools), Claude tried four different prompt modifications over approximately 40 minutes. Each attempt failed for the same reason: the write_calendar tool did not accept an attendees parameter.
Claude never explicitly stated that the parameter didn't exist. It just kept trying different prompt modifications.
The breakthrough
When the developer changed the approach and dumped all four debugging traces plus the source code into one context window, Claude immediately diagnosed the problem in about 10 seconds. The model identified: "The write_calendar tool does not accept an attendees parameter. The constraint is at the code level, not the instruction level."
Key insight
The same Claude model that spent 40 minutes on workarounds found the root cause in seconds when given the right framing. The developer noted: "The framing mattered more than the model. Same Claude, same code, different question."
Claude had generated the write_calendar tool itself, so it never occurred to the developer to check the function signature for missing parameters.
📖 Read the full source: r/ClaudeAI
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