Creating Copilot Hooks

Use this skill when the right answer is not more advice, but deterministic behavior at a specific lifecycle point. It helps design hooks that are safe, documented, and understandable.

When to Use

Use this skill when the user asks for things like:

• "create a Copilot hook for this policy"
• "block dangerous commands before they run"
• "log or validate tool usage automatically"
• "add a reusable hook pack with docs and scripts"
• "turn this manual guardrail into a hook"

Typical scenarios:

• pre-tool checks for risky shell commands
• post-tool validation or formatting triggers
• audit or observability hooks for shared environments
• installing a documented hook bundle for reuse across workspaces

Outcome Standard

A strong hook contribution usually includes:

• the right lifecycle event and the smallest useful behavior
• explicit safety defaults and clear denial or warning messages
• a documented hooks.json configuration
• cross-platform script guidance when Windows and Bash users both matter
• a README or pack that explains purpose, setup, and limitations

Hook Design Rules

• Start with observe or warn - block only when the policy is stable and the failure message is clear.
• Keep hooks fast - long-running hooks become friction generators instead of safeguards.
• Be explicit on denial - if a hook blocks work, explain exactly why and what to do instead.
• Separate policy from docs - the script enforces behavior; the README explains it.
• Prefer deterministic checks - hooks should not depend on fuzzy interpretation when avoidable.

Workflow

Phase 0: Decide whether a hook is the right primitive

Use a hook when deterministic automation is needed at a lifecycle event. If the need is guidance only, use instructions. If the need is a reusable workflow, use a skill. If the need is a user-started task, use a prompt.

Phase 1: Choose the lifecycle event

Clarify or infer:

• what event should trigger the hook
• whether the behavior is observe, warn, mutate, or deny
• how quickly the hook must complete
• whether it needs cross-platform script support

Phase 2: Design the safety model

Before scripting:

• define the exact condition being checked
• decide what the hook should output on allow, warn, or deny
• write the denial or warning message in user language, not policy jargon
• make sure the hook fails safely when inputs are missing or malformed

Phase 3: Create the hook pack

Use the resources below as the default starting point:

• ./resources/hook-template-pack.md
• ./resources/hook-example-pack.md

A complete pack should usually include:

• hooks.json
• one or more supporting scripts
• a README with purpose, setup, and behavior notes

Phase 4: Validate the operational fit

Check the result against ./resources/hook-quality-checklist.md.

Pay special attention to:

• whether the hook is fast enough for the event it runs on
• whether the messages are actionable
• whether Windows and non-Windows paths are addressed when required
• whether the hook blocks only what it truly means to block

Common Failure Modes

• using a hook when a normal instruction would have been enough
• blocking large classes of commands without a helpful reason
• writing scripts that are too slow for frequent lifecycle events
• shipping hooks.json without installation or behavior documentation
• creating platform-specific hooks with no fallback or adaptation guidance

Resource Map

• ./resources/hook-template-pack.md - template pack with README, config, and script scaffolds
• ./resources/hook-example-pack.md - worked example of a safe, documented policy hook
• ./resources/hook-quality-checklist.md - final review checklist before shipping

Definition of Done

A task using this skill is complete when:

• the hook behavior matches a clear lifecycle need
• the configuration, scripts, and documentation agree with each other
• failure, allow, and deny messages are understandable
• the pack is install-ready or clearly adapted for the target environment
• the final result passes the quality checklist without obvious operational risk