r/PromptEngineering: Developer Tests Whether Runtime Tool-Call Validation Still Matters After Strict Mode Ships — Finds It Catches a Distinct Class of Production Failures Strict Mode Cannot

A developer building DeFi risk infrastructure ran a systematic test to determine whether runtime tool-call validation layers remain necessary after strict/structured output mode shipped, which guarantees schema-valid tool calls at the API level. The conclusion: runtime validation still catches a distinct failure class — cases where the model emits a structurally valid schema but the declared action was never actually executed, a gap strict mode cannot close. The post argues for maintaining both layers in production agentic pipelines where a wrong answer can trigger real-world consequences.