When an MCP tool errors but the side effect already happened, what should the agent trust?
Street-Chest2270 · reddit · 2026-09-12
A Reddit post outlines an easily missed MCP failure mode: the agent calls createpayment(), the provider actually creates the payment, but the confirmation response times out — the agent sees an error and assumes nothing happened. Blind retry risks duplicate side effects, and tool logs don't resolve it since the tool can honestly report a transport failure while external state already changed. The author frames three questions: was the action authorized, was the evidence current at execution, and what external effect actually occurred — the first two checkable pre-execution, the third seemingly requiring independent post-execution observation or provider receipts. They ask operators of side-effecting MCP tools (payments, infra changes, bookings, access changes) what they treat as authoritative on conflict, and whether they test this failure mode before production.
More from coding & agent
- dhh on coding in the AI era: code is no longer the bottleneck, humans are — NERDDISCO · 2026-10-31
- pi-rs: Open Source Rust Port of the pi Coding Agent Ships pi-durable, No Node Needed — jasonkneen · 2026-10-31
- Open-source ComfyUI Motion Previs Studio brings 3D camera blocking to AI video — navarisun · 2026-10-31
- Replit agent drives Chrome via Computer Use in new demo, CEO Amjad Masad amplifies — amasad · 2026-10-31
- Every Used Codex and Agents to Survive the Railway Credential Breach — every · 2026-10-31
- Google's New /goto Anti-Bot Delay Hits SERP-Reselling Agent Search Firms — jobergum · 2026-10-31