Author(s): Chew Loong Nian – AI ENGINEER

Originally published on Towards AI.

Y Combinator Ditched All But One Claude Code Tool for 16 of Its Own

Y Combinator open-sourced the agent harness it runs its own company on. I read the adapter that boots Claude Code inside it, and found one line that takes away almost every tool Claude Code ships with, leaving at most 16 of QM’s own in their place — ten of them unconditional.

After identifying the key configuration line that disables nearly all Claude Code built-in tools, the article investigates the QM (Quartermaster) repo to explain what survives and why. The author shows that QM’s “fixed tool surface” is small—ten tools always available and sixteen at maximum—then details how a separate “read-only” mode filters the registry down further. They also walk through QM’s multi-vendor “harness router,” showing how the same underlying QM tool registry is marshaled across different platforms (Claude Code, Codex, OpenCode, and Pi) via multiple adapter transports, and how the system safely resets vendor sessions mid-conversation by storing the transcript in QM’s database. The piece further analyzes QM’s prompt “skills” overhead (including the cost of a “taste skill”), the design of context/memory handling, and the security posture controls that govern tool approvals and policy behavior across org scopes. Finally, it compares QM’s approach to other harness frameworks, summarizes the production cost drivers (durable per-scope sandboxes, infrastructure, and classifier overhead depending on posture), and concludes with a verdict on when QM’s vendor-neutral strategy is worth the complexity.

Read the full blog for free on Medium.

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Published via Towards AI