Getting it into your agent
This one installs as part of its plugin. Adding the marketplace and installing the plugin brings it with everything else the plugin ships.
/plugin marketplace add AraneaDev/cassandra/plugin install cassandraWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/hooks/araneadev/cassandra/post-tool-use-failure)<a href="https://agentmods.dev/hooks/araneadev/cassandra/post-tool-use-failure"><img src="https://agentmods.dev/badge/hooks/araneadev/cassandra/post-tool-use-failure.svg" alt="Measured on agentmods" height="20"></a>Grade A, and why
PostToolUseFailure 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 4d 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
63% identical to SessionStart — 9 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.
What it actually says
{
"PostToolUseFailure": [
{
"matcher": "^(Bash|mcp__.*)$",
"hooks": [
{
"type": "command",
"command": "\"$CLAUDE_PLUGIN_ROOT/bin/cassandra-hook\"",
"timeout": 2
}
]
}
]
}What else hooks.json configures
This page is one entry in a file that holds 6. Installing the file brings all of them; each is measured and scanned on its own page.
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.
- 4d ago First seen · 14 lines scan A 17b065b16402
PostToolUseFailure is a hook published in the GitHub repository AraneaDev/cassandra (1 stars, last pushed 3d ago), 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 63% identical to SessionStart, differing in 9 lines, and is treated as a copy.
Other hooks, from other repositories
SessionStart
Runs when a session starts, executing ensure-pane.sh and start.sh via bash (2 commands). From amaar-mc/claude-arcade.
UserPromptSubmit
Runs when you submit a prompt, before the agent sees it, executing play.sh via bash (2 commands). From amaar-mc/claude-arcade.
SessionEnd
Runs when a session ends, executing cleanup.sh via bash (2 commands). From amaar-mc/claude-arcade.
Stop
Runs when the agent finishes a response, executing pause.sh via bash (2 commands). From amaar-mc/claude-arcade.
SessionStart
Runs when a session starts, executing plugin-session-start.sh via bash. From openconclave/oc.
SessionStart
Runs when a session starts, executing update-check.js via node. From KevinZai/commander.