Claude Code hooks are user-defined commands and tools that execute automatically at fixed points in the agent's lifecycle, providing deterministic control over non-deterministic AI behavior. They form the third layer of control alongside permissions and CLAUDE.md instructions, guaranteeing certain actions always occur. The system includes 33 documented events, with five core hooks (PreToolUse, PostToolUse, UserPromptSubmit, SessionStart, Stop) handling most production use cases.
DeFi community discussions on September 21, 2026 cover Cardano's low DeFi audit score of 51.3/100 compared to Ethereum's 96.3, collaborations on Hedera's DeFi platforms, and concerns about malicious hooks in Uniswap v4 where 54% of analyzed hooks were identified as potentially harmful.
A CTO roundtable discussion reveals that coding agents pose unique security challenges because they hold user authority (filesystem, credentials, repositories) while receiving instructions from multiple sources. The article argues that critical rules—called invariants—should be enforced through system controls like permissions, hooks, and sandboxes rather than relying on prompt instructions, which models can ignore or be manipulated into violating.