PostToolUseFailure

PostToolUseFailure is a hook for Claude Code from danielmiessler/LifeOS. Its token cost is not measured, scanned A, original, MIT.

A failure hook that runs three commands after a tool call fails: EventLogger, AlgorithmNudge and LoopDetector.

In plain words
What is it for?
Recording failed tool calls, prompting a change in approach and detecting repeated failure loops.
Why use it?
It captures the failure and checks whether the agent needs a new approach or is repeating a loop.

Hook for Claude Code

Written for Claude Code: a Claude Code hooks.json.

One of 11 entries in hooks.json upstream. Installing this one merges just its entry into your config; the other 10 are separate, each on its own page.

Good fit Recording failed tool calls, prompting a change in approach and detecting repeated failure loops.

Compare 6 hooks from other repositories ↓
Install with agentmods
npx agentmods add hooks/danielmiessler/lifeos/post-tool-use-failure
About the project

LifeOS is an AI-assisted personal operating system that records a person’s goals, values, context, and current situation to help move them toward a desired future state. It supports work such as building applications, starting businesses, and creative projects. Its catalogue entries extend the system through skills, hooks, agents, and commands.

danielmiessler/LifeOS · 19,457 stars · on GitHub · ourlifeos.ai

Install

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.

Clone the repo
git clone --depth 1 https://github.com/danielmiessler/LifeOS

Made for: Claude Code.

Wrote 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.

agentmods badge for PostToolUseFailure

README.md
[![agentmods](https://agentmods.dev/badge/hooks/danielmiessler/lifeos/post-tool-use-failure/github.svg)](https://agentmods.dev/hooks/danielmiessler/lifeos/post-tool-use-failure)
Your own site
<a href="https://agentmods.dev/hooks/danielmiessler/lifeos/post-tool-use-failure"><img src="https://agentmods.dev/badge/hooks/danielmiessler/lifeos/post-tool-use-failure/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for PostToolUseFailure

Your own site · 80×15
<a href="https://agentmods.dev/hooks/danielmiessler/lifeos/post-tool-use-failure"><img src="https://agentmods.dev/badge/hooks/danielmiessler/lifeos/post-tool-use-failure.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session not measured What this adds to a session before it is invoked.
When invoked not measured Not applicable: nothing here is loaded into a session.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. ✓ AI security review Fable 5.1 · 7 Sept 2026 📄 Read the review
Origin original No closer match found in the catalogue.
Security

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 1mo 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.

LifeOS/install/hooks/hooks.json · 30 lines

What it actually says

{
  "PostToolUseFailure": [
    {
      "hooks": [
        {
          "type": "command",
          "command": "$HOME/.claude/hooks/EventLogger.hook.ts"
        }
      ]
    },
    {
      "hooks": [
        {
          "type": "command",
          "command": "$HOME/.claude/hooks/AlgorithmNudge.hook.ts",
          "timeout": 5
        }
      ]
    },
    {
      "hooks": [
        {
          "type": "command",
          "command": "$HOME/.claude/hooks/LoopDetector.hook.ts",
          "timeout": 5
        }
      ]
    }
  ]
}
Changes

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.

  1. 1mo ago First seen · 30 lines scan A 1f2658283928

Subscribe to this mod's changes

PostToolUseFailure is a hook published in the GitHub repository danielmiessler/LifeOS (19,457 stars, last pushed 1mo 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. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.