Building an MCP server for KNX/ETS projects: provenance tiers and fail-closed design

No-Recording-8313 · reddit · 2026-09-12

A developer open-sourced an MCP server (MIT) for ETS/KNX building automation projects, tackling the issue where models lose or invent group addresses when parsing large .knxproj files directly. Three prompt-agnostic lessons: tools return facts with provenance and confidence tiers (declared role > datatype > naming keywords) plus a dedicated "why did you decide this" tool; fail closed by routing any ambiguity to a review list instead of generated config (e.g. a 5.001 byte could be dimmer level or blind position); every field bug becomes a regression test. Read-only by construction, no bus library. Open question: handling large tool outputs — currently pagination and filtered views, weighing write-to-file-and-return-path instead.

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