Strategic Compact Skill

Suggests manual /compact at strategic points in your workflow rather than relying on arbitrary auto-compaction.

When to Activate

Running long sessions that approach context limits (200K+ tokens)
Working on multi-phase tasks (research → plan → implement → test)
Switching between unrelated tasks within the same session
After completing a major milestone and starting new work
When responses slow down or become less coherent (context pressure)

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:

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. A valid native compaction budget can lower the default reminder threshold to 80% of that budget; model-capacity percentages still use the resolved model window
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, capped at 80% of a valid native compaction budget when earlier). An explicit positive threshold overrides that default cap; 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 auto-compact trigger, which may be smaller than the model's context window. For context-window resolution, ECC uses it only as a last-resort fallback, after an explicit ECC override, a [1m] model marker, a known large-window model family, and inference from observed tokens above 200k. It is not an exact model-capacity declaration.

Window precedence is: ECC_CONTEXT_WINDOW_TOKENS, then the [1m] marker, a known large-window model family, observed tokens above 200k, the native auto-compact fallback, and finally the inferred 200k default. Set ECC_CONTEXT_WINDOW_TOKENS when you know the actual window and automatic detection lacks that information; do not treat the native compact trigger as proof of model capacity.

The Stop-hook summary scheduler protects resume state before compaction. It uses the earlier of confirmed capacity and a valid native compaction budget. When capacity is inferred, it uses only a valid native budget, or treats the remaining budget as unknown if none is provided. Model-capacity resolution remains separate. The default /compact reminder threshold independently uses the earlier of its window-scaled default and 80% of a valid native compaction budget. An explicit COMPACT_CONTEXT_THRESHOLD, including 0, remains authoritative.

Compaction Decision Guide

Use this table to decide when to compact:

Phase Transition	Compact?	Why
Research → Planning	Yes	Research context is bulky; plan is the distilled output
Planning → Implementation	Yes	Plan is written down (a file, or the task list if you have one); free up context for code
Implementation → Testing	Maybe	Keep if tests reference recent code; compact if switching focus
Debugging → Next feature	Yes	Debug traces pollute context for unrelated work
Mid-implementation	No	Losing variable names, file paths, and partial state is costly
After a failed approach	Yes	Clear the dead-end reasoning before trying a new approach

What Survives Compaction

Understanding what persists helps you compact with confidence:

Persists	Lost
CLAUDE.md instructions	Intermediate reasoning and analysis
Files on disk	File contents you previously read
Memory files (`~/.claude/memory/`)	Multi-step conversation context
Git state (commits, branches)	Tool call history and counts
The task list — only if you have the todo tools (see below)	Nuanced user preferences stated verbally

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

Compact after planning — Once the plan is finalized and written to a file, compact to start fresh
Compact after debugging — Clear error-resolution context before continuing
Don't compact mid-implementation — Preserve context for related changes
Read the suggestion — The hook tells you when, you decide if
Write before compacting — Save important context to files or memory before compacting
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%+:

Trigger	Skill	Load When
"test", "tdd", "coverage"	tdd-workflow	User mentions testing
"security", "auth", "xss"	security-review	Security-related work
"deploy", "ci/cd"	deployment-patterns	Deployment context

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)

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