PreCompact and PostCompact Hooks - Claude Code
Fire before and after context compaction.
PreCompact and PostCompact hooks let you control or observe when Claude compacts context to stay within the window.
What it does
PreCompact fires just before Claude summarizes older turns. It can block the compaction, customize the summary strategy, or persist important context before it gets condensed. PostCompact fires after compaction completes, receiving the before/after sizes and the summary used. It's the clean hook point for "make sure this important decision survives compaction".
When to use it
- Snapshotting state to disk before a compaction you're worried about.
- Injecting explicit "keep this" notes before summarization.
- Measuring compaction frequency for context-efficiency tuning.
- Auditing what the summarizer is choosing to forget.
Gotchas
- Aggressive PreCompact logic can delay long turns noticeably.
- Custom compaction strategies are powerful and easy to get wrong. Start with the default.
- PostCompact runs with the new, smaller context. The hook can't reference what was dropped.
Official docs: https://code.claude.com/docs/en/hooks.md#precompact
Continue Reading
- Claude Code - plans, install routes, and alternatives on one page
- Claude Code Power User course - wiring deterministic hooks like this one, plus skills and subagents
Technical content at the intersection of AI and development. Building with AI agents, Claude Code, and modern dev tools - then showing you exactly how it works.
Was this helpful?
Related Guides
Related Tools
Claude Agent SDK
Anthropic's SDK for building agents on the same tools, agent loop, and context management that power Claude Code. Python...
View Tool
Claude Code
Anthropic's agentic coding CLI. Runs in your terminal, edits files autonomously, spawns sub-agents, and maintains memory...
View ToolCodeburn
Interactive TUI dashboard that shows exactly where your Claude Code and Cursor tokens are going, in real time.
View ToolConductor
Mac app for running parallel Claude Code, Codex, and Cursor agents in isolated workspaces. Watch every agent work at onc...
View ToolRelated Videos
Generate Videos in Codex + Claude Code with This...
Check out HeyGen! https://heygen.1stcollab.com/developersdigest The video introduces HeyGen, an AI video generation platform with a rich API and a CLI that lets developers create, fetch, and manipula...
10x Design in Claude Code and Codex
Try Higgsfield: https://higgsfield.ai/s/higgsfield-general-campaign-developersdigest-juDMTi AI coding agents can build entire websites in minutes, but the default results often still look generic and...
Self Improving Applications with Claude Code & Codex
Build a Self‑Improving Next.js App: Supabase + Vercel Eve + GitHub Issues + Agent Loops Check out Supabase: https://supabase.plug.dev/1wWOTGS The video demonstrates how to build and deploy a self-im...
Related Posts
Claude Fable 5.1 in Claude Code: How to Switch, Pin, and Pay Less
Claude Code v2.1.257 points /model fable at Fable 5.1: 1M context, $10/$50 per MTok, $0.25 cache reads. Setup, gotchas,...
Claude Design, Slides and Docs in Any Chat: How to Use Them
Claude Design, Slides and Docs now open in any Claude chat, Claude Code session or the Artifacts tab, on every plan. Exa...
Claude for Startups Offer Paused: What Founders Do Now
Claude for Startups paused its free Claude Team year and $1,000 API credit offer at capacity. What the program page says...
Claude Advisor Tool vs a Bigger Model: When the Pairing Pays
Anthropic's own runs: a Fable 5.1 advisor added 1.7 points to Opus 5.5 for 2.1x the cost. When the Claude advisor tool p...
Claude Code Retry Watchdog: Keep Unattended Runs Alive
CLAUDE_CODE_RETRY_WATCHDOG=1 makes Claude Code wait out 429 and 529 errors instead of failing after 10 retries. When to...
Do Your Agent Hooks Fail Open? Claude Code vs Codex vs Cursor vs Gemini CLI
A guard hook that crashes, times out or points at a missing script lets the tool call through by default in Claude Code....
