A pre-compaction hook that runs a Python script before the agent's conversation context is shortened, whether the shortening is started manually or automatically.

Use it for tasks that must happen immediately before context compaction, such as saving session information or preparing a compact summary, subject to what the included script does.

It gives the script a chance to preserve or prepare information before older conversation details are removed from the active context.

PreCompact — Hook by msshives-gif

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/msshives-gif/claude-plugins/pre-compact

Clone the repo

git clone --depth 1 https://github.com/msshives-gif/claude-plugins

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

PreCompact 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.

plugins/compact-manager/hooks/hooks.json · 24 lines

What it actually says

{
  "PreCompact": [
    {
      "matcher": "manual",
      "hooks": [
        {
          "type": "command",
          "command": "python3 \"${CLAUDE_PLUGIN_ROOT}/hooks/precompact.py\" || python \"${CLAUDE_PLUGIN_ROOT}/hooks/precompact.py\" || true",
          "timeout": 5
        }
      ]
    },
    {
      "matcher": "auto",
      "hooks": [
        {
          "type": "command",
          "command": "python3 \"${CLAUDE_PLUGIN_ROOT}/hooks/precompact.py\" || python \"${CLAUDE_PLUGIN_ROOT}/hooks/precompact.py\" || true",
          "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.

2d ago First seen · 24 lines scan A f0f01263d62e

Subscribe to this mod's changes

PreCompact is a hook published in the GitHub repository msshives-gif/claude-plugins (2 stars, last pushed 5d 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.

Data and AI Languages claude-code claude-code-plugin hooks llm-observability subagents

PreCompact

Getting it into your agent

Grade A, and why

Nothing flagged

What it actually says

What this file has done since we first saw it

Other hooks, from other repositories

PreToolUse

Stop

SubagentStop

SessionStart

UserPromptExpansion

UserPromptSubmit