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On-call Reasoning Harness

1 post · Jul 2026

What this trail covers

Blueberry is a Slack-native on-call reasoning harness designed to shorten time to first insight (TTFI) and time to test theories (TTTT) for on-call engineers. Blueberry automatically triages alerts within Slack threads, providing grounded explanations by correlating historical data (postmortems, runbooks) with live operational signals and changes. It features a durable, tool-aware architecture with a layered Model Context Protocol (MCP) for shared and team-specific investigators, enabling faster

All Instacart trails
  1. Blueberry: Force Multiplier For The On-Call EngineerThis post details the architecture and design principles of Blueberry, Instacart's Slack-native on-call reasoning harness. It emphasizes the system's durability through a Postgres-backed durable queue for job management, its composition layer for resolving team-specific skills and MCP endpoints, and its three-tiered Model Context Protocol (MCP) surfaces (in-process, shared server, team-hosted) for flexible tool integration. The post highlights the agent's dynamic decision-making capabilities within a structured harness for reliability, and quantifies performance metrics like TTFI averaging 3 minutes and TTTT averaging 3 minutes for theory checks. It also provides a concrete example of SEV2 triage and an 8-turn PR exoneration scenario.