Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add hooks/chachamaru127/claude-code-harness/session-startgit clone --depth 1 https://github.com/Chachamaru127/claude-code-harnessGrade A, and why
SessionStart scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.
A static scan of the commands this hook runs, not an audit. A hook is shell that executes on your machine at the event it names, which is why every command in it is printed with what was found.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
This is a copy
98% identical to PreToolUse — 54 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 39 lines — stays where its author put it; the contents beside it link to each section on GitHub.
{
"SessionStart": [
{
"matcher": "startup|resume",
"hooks": [
{
"type": "command",
"command": "/bin/bash -c 'valid_root(){ local r=\"${1:-}\"; [ -n \"$r\" ] && [ -x \"$r/bin/harness\" ] && [ -f \"$r/.claude-plugin/plugin.json\" ] && /usr/bin/grep -q \"\\\"name\\\"[[:space:]]*:[[:space:]]*\\\"claude-code-harness\\\"\" \"$r/.claude-plugin/plugin.json\"; }; root=\"${CLAUDE_PLUGIN_ROOT:-}\"; if ! valid_root \"$root\"; then root=\"\"; for c in \"${CLAUDE_PROJECT_DIR:-}\" \"$PWD\" \"$HOME/.claude/plugins/marketplaces/claude-code-harness-marketplace\" \"$HOME/.claude/plugins/cache/claude-code-harness-marketplace/claude-code-harness/\"*; do if valid_root \"$c\"; then root=\"$c\"; break; fi; done; fi; if ! valid_root \"$root\"; then echo \"[claude-code-harness] plugin root not found; hook skipped\" >&2; exit 0; fi; exec \"$root/bin/harness\" \"$@\"' _ hook session-start",
"timeout": 15,
"once": true
},
{
"type": "command",
"command": "/bin/bash -c 'valid_root(){ local r=\"${1:-}\"; [ -n \"$r\" ] && [ -x \"$r/bin/harness\" ] && [ -f \"$r/.claude-plugin/plugin.json\" ] && /usr/bin/grep -q \"\\\"name\\\"[[:space:]]*:[[:space:]]*\\\"claude-code-harness\\\"\" \"$r/.claude-plugin/plugin.json\"; }; root=\"${CLAUDE_PLUGIN_ROOT:-}\"; if ! valid_root \"$root\"; then root=\"\"; for c in \"${CLAUDE_PROJECT_DIR:-}\" \"$PWD\" \"$HOME/.claude/plugins/marketplaces/claude-code-harness-marketplace\" \"$HOME/.claude/plugins/cache/claude-code-harness-marketplace/claude-code-harness/\"*; do if valid_root \"$c\"; then root=\"$c\"; break; fi; done; fi; if ! valid_root \"$root\"; then echo \"[claude-code-harness] plugin root not found; hook skipped\" >&2; exit 0; fi; exec \"$root/bin/harness\" \"$@\"' _ hook session-monitor",
"timeout": 30,
"once": true
},
{
"type": "command",
"command": "/bin/bash -c 'valid_root(){ local r=\"${1:-}\"; [ -n \"What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 2d ago First seen · 39 lines scan A 24b09699dd76
SessionStart is a hook published in the GitHub repository Chachamaru127/claude-code-harness (3,079 stars, last pushed yesterday), licensed MIT. Its token cost is not measured: a hook is shell that never enters the context. A static security scan graded it A with 0 findings. It is 98% identical to PreToolUse, differing in 54 lines, and is treated as a copy.
Other hooks, from other repositories
PostToolUse
Runs after a tool call finishes for Write and Edit tool calls, executing format_and_lint.sh. From supabase/supabase.
SessionStart
Runs when a session starts, executing on-start.js via node. From google-gemini/gemini-cli.
SessionStart
Runs when a session starts on startup, executing install_pkgs.sh. From supabase/supabase.
PreToolUse
Runs before the agent uses a tool, executing pre-write.sh and pre-bash.sh (2 commands). From anthropics/claude-cookbooks.
SessionStart
Runs when a session starts, executing session-start.sh. From anthropics/claude-cookbooks.
SessionStart
Runs when a session starts on startup, clear and compact, executing run-hook.cmd. From obra/superpowers.