PreToolUse hooks never fire under PowerShell profiles on Windows

Symptoms

Hooks that work on macOS/Linux teammates' machines do nothing on Windows. `claude --debug` shows the hook being matched but the command never runs; there's no stderr, no timeout, nothing. The dangerous part: people assumed their guardrail hooks (commit blockers, path denies) were active when they weren't. Only affects setups where the PowerShell profile writes to stdout during startup (fancy prompts, module load banners, oh-my-posh init).

Likely cause

On 2.3.x, Windows hook commands were spawned through `powershell -Command` with the user profile loaded. Profile stdout output corrupted the JSON the hook protocol expects on the first line, the parse failed, and the failure was swallowed as a no-op instead of surfacing. 2.4.0 spawns hooks with -NoProfile and treats parse failures as loud errors.

Affected

2.3.0 – 2.3.5; fixed in 2.4.0

Environments

Windows with a stdout-writing PowerShell profile (oh-my-posh, starship init via profile, module banners) · Windows 10, Windows 11

Confidence

High confidence · verified Jul 14, 2026

Upgrade to 2.4.0+ (or strip profile stdout on 2.3.x)

The real fix is upgrading — 2.4.0 spawns hook commands with -NoProfile and surfaces hook failures instead of swallowing them. If you're stuck on 2.3.x, silence your profile's startup output so the hook protocol stream stays clean, then verify hooks actually fire.

01

Upgrade and confirm the version:

claude update && claude --version

Copy

02

Verify hooks fire now — add a canary hook that writes a marker file, then trigger any tool call: