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Hooks follow the agent lifecycle.

Hooks are deterministic in a way skills are not:<br>a skill is a package of instructions and resources where the model judges how and when it should use a skill.<br>Whereas hooks always run during a preconfigured event, outside the model's decision-making.

Below are some of the events that a hook can be attached to. In addition to events, hooks can be attached<br>to specific tools: for example, an edit tool can be attached to a hook that automatically formats the output.

Input<br>UserPromptSubmit<br>block prompt or add context

Context<br>SessionStart<br>startup, resume, clear, compact

Prevent<br>PreToolUse<br>deny or rewrite the call

Escalate<br>PermissionRequest<br>allow, deny or defer to UI

Repair<br>PostToolUse<br>validate completed output

Complete<br>Stop<br>finish or force another pass

Teardown<br>SessionEnd<br>best-effort cleanup only

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How can lawyers use hooks?

Hooks are part of a defense in depth. They allow you to preserve privileged context, validate factual<br>evidence and reliably integrate version control.

Some examples

Legal control<br>Hook boundary<br>Example

Prevent<br>Enforce matter walls

PreToolUse<br>DENY

Deny a local or MCP call that targets another client's workspace or an unauthorised export path.

Repair<br>Check every document edit

PostToolUse<br>CHECK

Scan defined terms, clause numbering, cross-references and redline integrity, then return one precise repair instruction.

Prove<br>Refuse unsupported completion

Stop<br>REQUIRE

Require cited authorities, resolved drafting issues and a privilege check before releasing the final work product.

Handoff<br>Brief the next specialist

SubagentStop<br>HAND OFF TO<br>SubagentStart

Persist the issue, authorities, clause references and open risks, then brief the next specialist.

Version<br>Protect legal document history

PreToolUse<br>THEN RECORD<br>PostToolUse

Reject an edit built on a stale revision, then attach the accepted revision and provenance receipt to the legal document VCS.

Matter continuity and specialist handoffs

Subagents can be specialised for adversarial review, specifically testing certain legal assertions you make. You can fan out many of these subagents at once, to attack your drafting from multiple angles.

PreCompact<br>Seal the matter checkpoint<br>Before context is compressed

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PostCompact<br>Refresh the recovery record<br>After compaction succeeds

Save the client&rsquo;s instructions, agreed positions, current document version, open issues, sources still to check and the next task.

Note whether compaction was manual or automatic. Then update the matter summary and recovery index.

If the checkpoint cannot be saved and checked, stop before compaction. Do not risk losing a deadline, instruction or open issue.

SubagentStart<br>Issue a scoped brief<br>Role, matter access and required output

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SubagentStop<br>Test the evidence packet<br>Before accepting its result

Give each specialist only what it needs: the approved matter files, a clear question, approved sources, the privilege status and the current document version.

Ask it to cite the relevant clause or authority, state its assumptions and flag anything unresolved.

If evidence is missing, send the specialist back to finish the work. Otherwise, save a versioned handoff for the supervising lawyer or next specialist.

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Appraise hooks as part of a wider control system

Hooks are strongest when they test objective facts, enforce guardrails, and act as part of a wider logging<br>or audit system. They can be a key component in enforcing reliable and safe AI use by law firms.

Scope

Automate predicates, not conclusions

Use command hooks for checks with clear answers: is this the right matter, does the user have permission, is the document current, is there a citation, and has approval been recorded? Leave legal judgement—whether advice is right, a conflict can be waived, or material is privileged—to a lawyer.

Boundary

Stop disclosure before it occurs

Check client data, matter access and export destinations in PreToolUse, before the tool runs. Once information has been disclosed or a document has been changed, a later hook cannot undo it.

Supervision

Escalate uncertainty up the chain

Use Stop when the agent still needs evidence or sign-off. Send unresolved questions about authority, privilege or drafting to a lawyer. Passing a hook is not legal approval.

Operation

One owner; two speeds

Hooks triggered by the same event run at the same time. Give each deny or rewrite rule one owner. Keep immediate checks fast and local, and run deeper document checks at Stop. Treat the 600-second limit as a ceiling, not a target.

Data

Return the smallest safe delta

Return only what the agent needs to continue: the matter ID, revision ID and exact problem. Do not return a privileged document or a broad matter summary. Outputs of roughly 2,500 tokens may be written to temporary storage.

Evidence

Make...