SessionStart
Hook OfficialSecurity guidance plugin — pattern-based warnings on edits, git-diff-based LLM review on stop
Fires on
SessionStartOnce, as a session begins — before you type anything.
Where this sits in a session
- Session start→
- Prompt submitted→
- Prompt expansion→
- Before tool use→
- After tool use→
- Notification→
- Before compaction→
- Subagent finished→
- Turn finished→
- Session end
Observes only — Emits messages or context. It never returns a permission decision.
What it runs
Executed automatically when the event fires — no prompt, no confirmation.
bash "${CLAUDE_PLUGIN_ROOT}/hooks/sg-python.sh" "${CLAUDE_PLUGIN_ROOT}/hooks/ensure_agent_sdk.py"Install it yourself
Paste into .claude/settings.json to run this hook without installing the whole plugin. Adjust the paths to point at your own copy of the scripts.
{
"hooks": {
"SessionStart": [
{
"hooks": [
{
"type": "command",
"command": "bash \"${CLAUDE_PLUGIN_ROOT}/hooks/sg-python.sh\" \"${CLAUDE_PLUGIN_ROOT}/hooks/ensure_agent_sdk.py\"",
"timeout": 180
}
]
}
]
}
}Source (2 files)
Read this before installing — it runs on your machine with your permissions.
#!/usr/bin/env bash
# Find a working Python 3 interpreter and exec the hook with it.
#
# On Windows + Git Bash, `python3` typically resolves to the Microsoft Store
# stub at C:\Users\<user>\AppData\Local\Microsoft\WindowsApps\python3, which
# exits 49 silently in non-TTY subprocess context (a known Microsoft Store
# stub behavior). This shim
# probes each candidate with `-c ""` and skips any that fails, so the Store
# stub falls through to the real python.org install (`python` in Git Bash) or
# the `py -3` launcher.
#
# Order:
# 1. python3 — canonical on macOS/Linux; the Store stub fails the probe.
# 2. python — python.org installs on Windows; some Linux distros (RHEL 7
# EOL'd 2024-06) point this at Python 2, but `-c ""` succeeds
# on Python 2 too — guard with a version check.
# 3. py -3 — Windows Python launcher.
#
# Args after the shim path are passed straight through to the chosen
# interpreter, so the hooks.json invocation is:
# bash "${CLAUDE_PLUGIN_ROOT}/hooks/sg-python.sh" \
# "${CLAUDE_PLUGIN_ROOT}/hooks/security_reminder_hook.py"
set -e
# Force UTF-8 for ALL Python filesystem + IO operations (PEP 540).
# Without this, Windows Python defaults `locale.getpreferredencoding()` to
# cp1252 — which makes `text=True` in subprocess.run / open() / json.load
# crash the internal reader thread on any byte that's undefined in cp1252
# (e.g. the 0x81 byte from ف, present in any path/filename with
# Arabic/Hebrew/CJK characters). See #2056, #2099.
#
# No-op on macOS/Linux (already UTF-8). Must be set BEFORE Python starts —
# changing it from inside the interpreter has no effect.
export PYTHONUTF8=1
# Git Bash / MSYS on Windows hands script paths to this shim in POSIX form
# (`/c/Users/...`). When we exec a Windows `python.exe` (which we do on
# Windows since `python3` is the Microsoft Store stub), python interprets the
# leading `/` as the root of the current drive — e.g. `/c/Users/...` becomes
# `C:\c\Users\...` or `D:\c\Users\...` (whichever drive the shell is on),
# fails with ENOENT, and every Edit/Write/MultiEdit tool use blocks until the
# session restarts. See anthropics/claude-plugins-official#2043.
#
# Fix: convert absolute path args to native Windows form via `cygpath -w`
# before exec. `cygpath` is a Git Bash builtin; it's absent on macOS/Linux,
# where the `command -v` guard makes this a no-op. `cygpath -w` is idempotent
# for already-Windows paths so the rare mixed-form case is safe.
if command -v cygpath >/dev/null 2>&1; then
converted=()
for a in "$@"; do
case "$a" in
/*) converted+=("$(cygpath -w "$a")") ;;
*) converted+=("$a") ;;
esac
done
set -- "${converted[@]}"
fi
probe() {
# $1..N: the interpreter command (may be multi-word like `py -3`)
# Writes "<major>.<minor>" to stdout and exits 0 iff at least Python 3.
"$@" -c 'import sys; print(f"{sys.version_info[0]}.{sys.version_info[1]}")' 2>/dev/null
}
# True iff arg is a "M.m" version string >= 3.10. claude_agent_sdk requires
# Python >= 3.10; below that, pip install fails ("No matching distribution")
# and the LLM-powered review (Stop / commit / push) silently no-ops while
# pattern checks (PostToolUse regex) keep working. macOS ships 3.9.6 as the
# default `python3` on current versions, so this guard matters in practice.
# See anthropics/claude-plugins-official#2071.
is_sdk_compatible() {
case "$1" in
3.1[0-9]|3.[2-9][0-9]|[4-9].*|[1-9][0-9].*) return 0 ;;
*) return 1 ;;
esac
}
# Pass 1 — try minor-versioned binaries in descending order. These are only
# present if the user explicitly installed them (Homebrew / python.org / pyenv),
# so picking one here always upgrades over the system `python3`. Highest
# available wins; the user doesn't have to PATH-prefer it.
for cmd in "python3.13" "python3.12" "python3.11" "python3.10"; do
v=$(probe "$cmd") || continue
if is_sdk_compatible "$v"; then
exec "$cmd" "$@"
fi
done
# Pass 2 — bare interpreters, but only if SDK-compatible. Covers Linux distros
# that ship 3.10+ as the default `python3`, and Windows where `python` /
# `py -3` resolves to the user's python.org install.
for cmd in "python3" "python" "py -3"; do
# shellcheck disable=SC2086
v=$(probe $cmd) || continue
if is_sdk_compatible "$v"; then
# shellcheck disable=SC2086
exec $cmd "$@"
fi
done
# Pass 3 — fallback to any Python 3, even <3.10. Pattern-based checks
# (PostToolUse regex on Edit/Write) only need 3.6+ and are useful on their
# own; the SDK-dependent paths will detect the version mismatch and degrade
# inside the Python code. Without this fallback, the entire plugin would
# stop working on default macOS, which is a regression vs today.
for cmd in "python3" "python" "py -3"; do
# shellcheck disable=SC2086
v=$(probe $cmd) || continue
# Accept anything that successfully reported a "M.m" string.
case "$v" in
[0-9]*.[0-9]*)
# shellcheck disable=SC2086
exec $cmd "$@"
;;
esac
done
echo "security-guidance: no working Python 3 interpreter found." >&2
echo " tried: python3.13, python3.12, python3.11, python3.10, python3, python, py -3" >&2
echo " on Windows, install Python from https://python.org (NOT the Microsoft Store)" >&2
echo " on macOS, install Python 3.10+ via Homebrew (\`brew install python\`)" >&2
exit 1
Shipped by 1 plugin
Installing any of these installs this hook.
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