PostToolUse

PostToolUse is a hook for Claude Code from Kasempiternal/axiom-v2. Its token cost is not measured, scanned A, original, MIT.

A post-tool hook that runs a small shell check after Bash, Write, or Edit operations finish. It scans the tool output for familiar error messages and suggests related debugging guides or commands.

In plain words
What is it for?
Use it to add automatic hints after tool calls, especially in projects involving SwiftUI layout, concurrency, databases, memory, iCloud, or build configuration.
Why use it?
It can point the coding agent toward likely fixes when tool output shows layout conflicts, concurrency errors, database migration problems, memory leaks, cloud errors, or build failures.

Hook for Claude Code

Written for Claude Code: PostToolUse hook event.

Part of the axiom plugin — 40 skills, 8 commands, 12 agents, 2 hooks shipped together

One of 2 entries in hooks.json — they are configured in one file and arrive together.

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.

agentmods
npx agentmods add hooks/kasempiternal/axiom-v2/post-tool-use
Clone the repo
git clone --depth 1 https://github.com/Kasempiternal/axiom-v2

Made for: Claude Code.

Or install axiom, the plugin that ships this one along with the rest of its 40 skills, 8 commands, 12 agents, 2 hooks.

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 PostToolUse

README.md
[![agentmods](https://agentmods.dev/badge/hooks/kasempiternal/axiom-v2/post-tool-use.svg)](https://agentmods.dev/hooks/kasempiternal/axiom-v2/post-tool-use)
Your own site
<a href="https://agentmods.dev/hooks/kasempiternal/axiom-v2/post-tool-use"><img src="https://agentmods.dev/badge/hooks/kasempiternal/axiom-v2/post-tool-use.svg" alt="Measured on agentmods" 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. Scan, not verified.
Origin original No closer match found in the catalogue.
Security

Grade A, and why

PostToolUse 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 5d 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.

axiom-plugin/hooks/hooks.json · 22 lines

What it actually says

{
  "PostToolUse": [
    {
      "matcher": "Bash",
      "hooks": [
        {
          "type": "command",
          "command": "bash -c 'O=\"$CLAUDE_TOOL_OUTPUT\"; echo \"$O\" | grep -qE \"Unable to simultaneously satisfy constraints\" && echo \"Tip: Auto Layout conflict — load ax-uikit\"; echo \"$O\" | grep -qE \"Actor-isolated|Sendable|data race|@MainActor\" && echo \"Tip: Concurrency issue — load ax-concurrency\"; echo \"$O\" | grep -qE \"no such column|FOREIGN KEY constraint|migration\" && echo \"Tip: Database migration issue — load ax-grdb or ax-swiftdata\"; echo \"$O\" | grep -qE \"retain cycle|memory leak|deinit.*never called\" && echo \"Tip: Memory issue — load ax-performance\"; echo \"$O\" | grep -qE \"CKError|CKRecord.*error|ubiquitous.*error|iCloud Drive|NSFileCoordinator\" && echo \"Tip: Cloud sync issue — load ax-cloud-storage\"; echo \"$O\" | grep -qE \"error:.*module.*not found|linker command failed\" && echo \"Tip: Build issue — /axiom:fix-build\"; exit 0'"
        }
      ]
    },
    {
      "matcher": "Write|Edit",
      "hooks": [
        {
          "type": "command",
          "command": "bash -c 'if [[ \"$TOOL_INPUT_FILE_PATH\" == *.swift ]] && command -v swiftformat &>/dev/null; then swiftformat \"$TOOL_INPUT_FILE_PATH\" --quiet || true; fi; exit 0'"
        }
      ]
    }
  ]
}
Same file

What else hooks.json configures

This page is one entry in a file that holds 2. Installing the file brings all of them; each is measured and scanned on its own page.

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. 5d ago First seen · 22 lines scan A 8ec75966e2e6

Subscribe to this mod's changes

PostToolUse is a hook published in the GitHub repository Kasempiternal/axiom-v2 (4 stars, last pushed 6mo 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 2026-08-31.