AgentHook Glossary

AgentHook

AgentHook is an open technical specification for AI agent runtime evidence: lifecycle events, tool calls, approvals, denials, model interactions, publisher manifests, and runtime control attestations expressed in one subscriber-addressable envelope. AgentHook defines the data model, not the implementation.

See also: HookBus (the reference implementation), runtime evidence, lifecycle hook. Canonical citation: Ruocco, P. (2026). AgentHook: A Runtime Evidence Standard for Auditable AI Agent Governance. Zenodo. 10.5281/zenodo.20112580.

Runtime evidence

Tamper-evident records of what an autonomous AI agent did at execution time, why it was allowed to act, what reasoning was exposed, and what happened next. Runtime evidence sits between policy intent and audit, providing the auditable record on which EU AI Act Article 12, ISO/IEC 42001, and SOC 2 controls depend.

Distinct from observability (which is for operators) and from logs (which are unstructured). Runtime evidence is structured, signed, and regulator-addressable.

Lifecycle hook

A canonical event emitted by an AI agent runtime at a defined point in execution. AgentHook standardises ten lifecycle hooks: SessionStart, UserPromptSubmit, PreLLMCall, PostLLMCall, ModelResponse, PreToolUse, PostToolUse, AgentHandoff, ErrorOccurred, and SessionEnd.

A runtime that emits AgentHook-conformant lifecycle hooks is a publisher.

Publisher

An AI agent runtime, assistant, coding tool, SDK, CLI, or workflow runner that emits AgentHook lifecycle events. Reference publisher shims exist for Claude Code, Codex CLI, AmpCode, OpenCode, Hermes Agent, and OpenClaw. Anthropic Agent SDK and OpenAI Agents SDK shims are in private beta.

A publisher is paired with one or more subscribers via a bus such as HookBus.

Subscriber

A service that consumes AgentHook lifecycle events from a bus and observes, gates, enriches, redacts, approves, denies, or audits the action. Subscribers can be synchronous (blocking the agent action until they decide) or asynchronous (recording evidence without blocking).

Subscribers built by the steward, most not yet publicly released, include AgentProtect CRE (policy gate), AgentAuditor (evidence log), AgentFlow (human approval), AgentKnowledge (policy context), AgentNotify (incident alerts), AgentRegistry (sanctioned-AI control), AgentIntelligence (LLM gateway), and AgentSpend (cost tracking).

Admissibility gate

A pre-execution decision boundary at which an AI agent's intended action is evaluated against policy and either allowed, denied, or paused for human approval before any side effect occurs. The admissibility gate is the atomic point at which runtime evidence becomes load-bearing for governance, audit, and regulatory obligations.

Evidence pack

An exportable bundle of AgentHook runtime evidence covering a defined session, tenant, or audit window. Evidence packs are tamper-evident (typically SHA-256 hash chained), human-readable, machine-parseable, and formatted for the regulator, auditor, or assurance reviewer that the implementing organisation reports to.

Evidence packs are intended to be produced by an audit subscriber (the steward's AgentAuditor recorder does not yet export them) and consumed by external assurance, internal audit, regulators, and incident response.

HookBus

HookBus is the open-source reference event bus that implements the AgentHook specification. The bus is Apache 2.0 licensed; reference publisher shims are MIT. UK patent application GB2608069.7.

A runtime is AgentHook-conformant if its publisher emits the canonical lifecycle hooks and a bus or subscriber can consume them. HookBus is one such bus; the standard does not require it.