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Claude Code hooks can make selected checks automatic: block defined risky actions, run feedback after edits, verify work at the end of a turn, and watch for changes to the policies governing those checks. They cannot prove code is correct or make every malicious action impossible. The practical goal is narrower: make specific failures harder to overlook by moving checks out of memory and into the tool lifecycle.
What hooks can—and cannot—do
A hook is a command or handler associated with a Claude Code lifecycle event. Depending on the event, it can inspect a proposed action, respond after a tool runs, validate a turn, or react to a configuration change. The event and matcher determine what the hook sees and whether it can block an action; a check attached to one tool does not automatically cover other ways of changing files. See Anthropic’s hooks guide and hooks reference.
These five patterns are a practical selection from documented capabilities, not an Anthropic-provided bundle or a configuration with published effectiveness measurements. Start with a real failure in your workflow, select the narrowest useful matcher, and test both the expected success and failure paths.
Five hooks to consider
| Hook pattern | When it runs | What it can do | Coverage and limitation |
|---|---|---|---|
| Block defined dangerous shell actions | PreToolUse | Deny selected commands before execution | Only the matched tool and conditions; broad patterns can disrupt ordinary work |
| Protect sensitive paths | PreToolUse | Deny edits or writes to paths designated by project policy | Only matched file tools and correctly recognized paths |
| Run focused formatting or lint feedback | PostToolUse | Run a fast check after a matched tool succeeds | After-the-fact feedback; Edit/Write matching does not observe shell-based writes |
| Run a completion check | Stop | Run a defined test or validation command at turn completion | Reports the result of that check, not correctness beyond its coverage |
| Watch policy changes | ConfigChange | Audit or block selected configuration changes | Does not replace filesystem controls or review of hook code |
1. PreToolUse: deny explicitly dangerous shell actions
Use a PreToolUse hook to inspect a planned Bash command before it runs and deny only clearly defined high-risk cases. Anthropic’s documentation includes a destructive-shell-command example. If your environment uses PowerShell, account for it explicitly rather than assuming a Bash matcher covers it. Keep the rules narrow: a pattern that catches ordinary commands can turn a guardrail into a source of needless interruptions.
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Test representative commands that should be denied and nearby commands that should remain allowed. Make the decision understandable in the result or log so a developer can see why the action was blocked.
2. PreToolUse: protect project-sensitive paths
Use a separate PreToolUse check for Edit and Write targets covered by your project’s policy. Depending on the repository, that might include secrets, generated files, or lock files that should only change through a designated process. Normalize paths before comparing them with protected locations; test allowed and denied paths, including equivalent path forms, so the rule cannot be bypassed by a spelling difference.
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This protects the file-tool actions the matcher observes. It is not a universal filesystem boundary: a shell command can also change files, so a file-edit matcher alone does not cover every write route.
3. PostToolUse: return fast formatting or lint feedback
Attach a PostToolUse hook to relevant tools such as Edit and Write, then run a quick, deterministic formatter or linter. This gives Claude feedback close to the change and can catch mechanical issues before they accumulate. Because PostToolUse runs after the matched tool action, it is feedback after the write—not a pre-write block.
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Choose the matcher with the coverage limitation in mind: shell commands can modify files without invoking Edit or Write. Keep the check fast enough to run routinely, and make its output useful rather than merely reporting an opaque failure.
4. Stop: run a deterministic completion check
A Stop hook can run the project’s chosen fast test or validation command when Claude reaches the end of a turn. Anthropic’s power-user guidance recommends verification as a way to let Claude check its own output. Make the check explicit and report the actual command outcome; a model-generated statement that tests passed is not test evidence.
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Choose validation that fits the repository: a focused test command, a build check, or another deterministic validation. A passing result establishes only that the selected check passed under its conditions. Tests exercise covered behavior; they do not prove untested behavior correct.
5. ConfigChange: watch the guardrails themselves
Use ConfigChange to record or block unexpected changes to settings, skills, or policy files during a session. Anthropic documents this event as able to block a configuration change from taking effect. Monitoring this surface helps catch silent drift in the rules intended to constrain a session.
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It does not make executable hook code trustworthy by itself. Review the hook scripts and control what they can access; a policy-change hook is one layer, not a substitute for those controls.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to introduce hooks without creating false confidence
- Pick one observed failure. Decide whether the problem is a risky command, a protected file being changed, a missing mechanical check, an unverified completion, or an unexpected policy edit.
- Match only the relevant event and target. A shell-action rule, an Edit/Write path rule, and an end-of-turn test address different points in the lifecycle. Do not assume one matcher sees actions handled by another tool.
- Exercise both outcomes. Confirm the intended action is allowed, the defined risky case is blocked or reported, and the result is understandable to a human.
- Keep an inspectable record. Record enough context to understand which check ran and what it decided, without passing secrets to processes that do not need them.
- Review executable hook changes. Hook commands run locally with the user’s permissions. Treat their code as privileged: inspect it, quote and validate inputs, and prefer explicit paths.
- Expand only when the first check proves useful. Add another narrowly scoped hook for another real failure instead of installing a broad collection of rules by default.
Do not solve friction by automatically approving every permission prompt. Anthropic warns that broad matching can approve every permission prompt, including shell commands and writes. Also account for concurrent handlers: matching hooks may run concurrently, and one hook’s denial does not stop sibling hooks from running. Avoid side effects in another handler that assume a denial will prevent them.
What each check actually establishes
- A formatter reports formatting according to its rules; it does not validate application behavior.
- A linter reports configured rule violations; its coverage depends on the rules and files it checks.
- A test command reports its result for the tests run; a passing suite does not establish correctness outside their coverage.
- A pre-action denial establishes that the matched action was denied under the hook’s conditions, not that all alternate routes to the same effect are blocked.
- A configuration-change check can audit or block changes it observes; it does not replace review of trusted hook code or control of filesystem access.
Describe outcomes concretely: name the checks that ran and whether they passed, failed, or were not run. Anthropic’s advice that verification is impactful is qualitative guidance, not a measured success rate for this particular five-hook selection. No published controlled result establishes an effectiveness percentage for this configuration.
Optional: restore concise context after compaction
For a long session, a SessionStart hook with a compact matcher can re-inject a short set of critical conventions after context compaction. Anthropic documents this as a context-restoration pattern. Keep the injected material concise and treat it as a reminder, not enforcement: deterministic checks and explicit blocking belong in the relevant hooks.
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