Strategic Context Compacting

Why Strategic Compaction?

Auto-compaction triggers at arbitrary points:

• Often mid-task, losing important context
• No awareness of logical task boundaries
• Can interrupt complex multi-step operations

Strategic compaction at logical boundaries:

• After exploration, before execution — Compact research context, keep implementation plan
• After completing a milestone — Fresh start for next phase
• Before major context shifts — Clear exploration context before different task

How It Works

The suggest-compact.js script runs on PreToolUse (Edit/Write) and combines two signals:

1. Context size (primary) — Reads the latest usage record from the session transcript (transcript_path in the hook payload) and sums input_tokens + cache_read_input_tokens + cache_creation_input_tokens (the true context size of the turn). Suggests /compact at a window-scaled threshold — 160k tokens on a 200k window, 250k on a 1M window (detected from a [1m] model marker, or inferred when observed tokens already exceed 200k) — and re-reminds after every additional 60k tokens of context growth
2. Tool-call count (secondary) — Counts tool invocations in session; suggests at a configurable threshold (default: 50 calls), then every 25 calls after

Tool count alone is a weak proxy for window pressure: a few large file reads or MCP responses can fill the window in very few calls, while many tiny calls can cross 50 with a near-empty window. The context-size signal fires when it actually matters.

Hook Setup

Installed as a plugin? No setup is needed. The plugin's hooks/hooks.json already registers suggest-compact.js (hook id pre:edit-write:suggest-compact, active in the standard and strict hook profiles). Do not copy the block below into ~/.claude/settings.json — ~/.claude/scripts/ does not exist on plugin installs, and duplicating a plugin hook causes double execution.

If installed manually (./install.sh), add to your ~/.claude/settings.json:

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Edit",
        "hooks": [{ "type": "command", "command": "node ~/.claude/scripts/hooks/suggest-compact.js" }]
      },
      {
        "matcher": "Write",
        "hooks": [{ "type": "command", "command": "node ~/.claude/scripts/hooks/suggest-compact.js" }]
      }
    ]
  }
}

Configuration

Environment variables:

• COMPACT_THRESHOLD — Tool calls before first suggestion (default: 50)
• COMPACT_CONTEXT_THRESHOLD — Context tokens before the context-size suggestion (default: 160000 on a 200k window, 250000 on a 1M window; 0 disables the context signal)
• COMPACT_CONTEXT_INTERVAL — Additional context tokens before the suggestion repeats (default: 60000)
• COMPACT_STATE_TTL_DAYS — Days before stale per-session state files in the temp dir are swept (default: 14)
• ECC_CONTEXT_WINDOW_TOKENS — Explicit context-window size, in tokens, overriding auto-detection. Set this for large-window models whose reported id lacks a [1m] marker (e.g. 400k Opus 4.x, or a new 1M-window model family) so the threshold scales to the real window instead of defaulting to 200k and overstating context usage.
• CLAUDE_CODE_AUTO_COMPACT_WINDOW — Claude Code's native window-size override, in tokens; honored as a fallback when ECC_CONTEXT_WINDOW_TOKENS is unset.

The context window is otherwise auto-detected from a [1m] model marker or inferred when observed tokens already exceed 200k. On a large-window model that carries neither signal, set one of the overrides above so the /compact suggestion fires at the right point.

Compaction Decision Guide

Use this table to decide when to compact:

What Survives Compaction

Understanding what persists helps you compact with confidence:

Don't rely on the task list surviving — it may not exist

Claude Code 2.1.233 removed the todo/task tools by default on Opus 4.8, Sonnet 5, Fable 5, Mythos 5 and newer models (TodoWrite, TaskCreate/Get/Update/List). CLAUDE_CODE_ENABLE_TODO_TOOLS=1 brings them back, but that is a per-machine environment setting — it does not travel with this skill, so you cannot assume the reader has it.

This matters because "my todo list survives compaction" is a reason people compact instead of writing state down. If the tools are absent there is no list to survive, and the plan is simply gone. Write the plan to a file before compacting — a file persists on every version and every model. Treat the task list as a convenience that may be missing, never as your durable record.

Best Practices

1. Compact after planning — Once the plan is finalized and written to a file, compact to start fresh
2. Compact after debugging — Clear error-resolution context before continuing
3. Don't compact mid-implementation — Preserve context for related changes
4. Read the suggestion — The hook tells you when, you decide if
5. Write before compacting — Save important context to files or memory before compacting
6. Use /compact with a summary — Add a custom message: /compact Focus on implementing auth middleware next

Token Optimization Patterns

Trigger-Table Lazy Loading

Instead of loading full skill content at session start, use a trigger table that maps keywords to skill paths. Skills load only when triggered, reducing baseline context by 50%+:

Context Composition Awareness

Monitor what's consuming your context window:

• CLAUDE.md files — Always loaded, keep lean
• Loaded skills — Each skill adds 1-5K tokens
• Conversation history — Grows with each exchange
• Tool results — File reads, search results add bulk

Duplicate Instruction Detection

Common sources of duplicate context:

• Same rules in both ~/.claude/rules/ and project .claude/rules/
• Skills that repeat CLAUDE.md instructions
• Multiple skills covering overlapping domains

Context Optimization Tools

• token-optimizer MCP — Automated 95%+ token reduction via content deduplication
• context-mode — Context virtualization (315KB to 5.4KB demonstrated)

Related

• The Longform Guide — Token optimization section
• Memory persistence hooks — For state that survives compaction
• continuous-learning skill — Extracts patterns before session ends