Hooks / context

Re-inject project context after compaction

Restores your project's key facts into Claude's context right after a compaction wipes the details.

What it does

Fires on SessionStart with the compact matcher - the moment after context compaction. The script prints your standing context (stack, commands, conventions - edit the heredoc) to stdout, and SessionStart stdout is added to Claude's context. Official-guide pattern. Keep the output short; it rides along for the rest of the session.

When it runs

Config

Merge this into .claude/settings.json - or use the generator to combine hooks.

{
  "hooks": {
    "SessionStart": [
      {
        "hooks": [
          {
            "type": "command",
            "command": "${CLAUDE_PROJECT_DIR}/.claude/hooks/reinject-context-compact.sh",
            "timeout": 10
          }
        ],
        "matcher": "compact"
      }
    ]
  }
}

Script

Save as .claude/hooks/reinject-context-compact.sh and chmod +x it.

#!/bin/bash
# reinject-context-compact: print standing context after compaction.
# SessionStart stdout is added to Claude's context - keep this SHORT.
cat <<'CTX'
Project context (re-injected after compaction):
- Stack: <your stack, e.g. Next.js 15 + Postgres>
- Test command: <your test command>
- Conventions: <3-5 bullets Claude keeps forgetting>
CTX
exit 0

Install

1. Save the script to .claude/hooks/reinject-context-compact.sh and chmod +x it.
2. Edit the heredoc: 5-10 lines of the context Claude always needs.
3. Add the config fragment to .claude/settings.json.

Test it

• Positive: run /compact, then ask Claude a question that depends on the injected facts - it should answer without re-reading files.
• Negative: on a fresh session start (startup matcher), this hook must NOT fire - that is what the matcher is for.

Sources

• Claude Code hooks reference (checked 2026-09-10)
• Claude Code hooks guide (checked 2026-09-10)

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