Agent tools can't tell you if they actually succeeded: LangChain SQL test found
Internal-Chapter1526 · reddit · 2026-09-28
A developer testing LangChain found that agent tools often report success falsely: QuerySQLDataBaseTool returns identical output whether an UPDATE actually changed rows or matched zero rows, making success indistinguishable from failure.
A file-write tool showed the same issue — it claimed "saved" while the file was untouched, only detectable by comparing file hash/size before and after the call. The author built a wrapper that automatically performs before/after state checks instead of trusting tool return values — a useful pattern for anyone building reliable agents.
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