Context manager

Context Manager

Prevent information loss when your Claude Code context window fills up. Automatically tracks usage, saves state, and restores after restart.

When to Activate

• User says /ctx or /ctx save or /ctx check
• User asks about context usage or remaining space
• User is working on a long task that might exhaust context
• Before starting a large task (reading many files, big implementation)

The Problem

Claude Code has a finite context window. When it fills up:

• The system compresses earlier messages (lossy)
• You lose working state, partial progress, and nuanced context
• Multi-step tasks break halfway through
• You repeat work you already did

Instructions

/ctx check — Check Current Usage

Read the context-usage.json file (updated by Claude Code hooks):

cat .claude/state/context-usage.json 2>/dev/null

Report to the user:

• Green (>60% remaining): Plenty of room. Work freely.
• Yellow (40-60% remaining): Getting warm. Save state before starting big tasks.
• Red (<40% remaining): Save state now. Consider restarting before continuing.

If no tracking file exists, guide setup (see Setup section).

/ctx save — Save Current State

Capture everything needed to resume after a restart:

1. Create state file at .claude/state/assistant-state.md:

# Assistant State

**Saved**: {ISO timestamp}
**Reason**: {why saving — manual save, low context, task checkpoint}

## Current Task
{What you're working on right now}

## What's Done
{Completed steps, with file paths and commit hashes}

## What's Next
{Remaining steps, in order}

## Key Context
{Important facts that would be lost — variable names, design decisions,
 user preferences expressed during this session, error messages that
 led to the current approach}

## Open Files
{Files currently being worked on, with relevant line ranges}

2. Confirm save — tell the user what was captured

/ctx restore — Restore After Restart

At session start, check for saved state:

cat .claude/state/assistant-state.md 2>/dev/null

If state exists:

1. Read and internalize the saved context
2. Summarize to the user: "Picking up where we left off — [task summary]"
3. Continue from "What's Next"

/ctx auto — Enable Automatic Management

Set up a hook that monitors context usage and auto-saves:

Create .claude/hooks/context-watchdog.json:

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": { "tool_name": "*" },
        "hooks": [
          {
            "type": "command",
            "command": "node -e \"const f='.claude/state/context-usage.json';const fs=require('fs');try{const d=JSON.parse(fs.readFileSync(f));if(d.remaining_percentage<35){fs.writeFileSync('.claude/state/context-watchdog-triggered','1');console.log('CONTEXT LOW: '+d.remaining_percentage+'% remaining. Run /ctx save now.')}}catch(e){}\""
          }
        ]
      }
    ]
  }
}

This checks context after every tool use and warns when it's getting low.

State File Best Practices

What to Save

• Current task description and progress
• File paths and line numbers being worked on
• Commit hashes of completed work
• Design decisions made during this session
• User preferences expressed (e.g., "keep it simple", "use TypeScript")
• Error messages that informed the current approach
• Open questions or blockers

What NOT to Save

• Full file contents (they're on disk — just save the path)
• Entire conversation history (save the conclusions, not the discussion)
• Stale information from earlier in the session that was superseded

Save Points

Good times to save:

• After completing a story or task step
• Before reading a large file or codebase exploration
• Before switching topics
• When the user takes a break
• After resolving a tricky bug (save the solution context)

Setup

Minimal Setup (5 minutes)

1. Create the state directory:

mkdir -p .claude/state

2. Use /ctx save and /ctx restore manually

Full Setup (15 minutes)

1. Create state directory and context tracking:

mkdir -p .claude/state
echo '{}' > .claude/state/context-usage.json

2. Add a Claude Code hook to track context usage (requires Claude Code hooks support)

3. Run your Claude Code session inside tmux for clean restart support:

tmux new-session -s claude "claude"

4. Enable /ctx auto for automatic warnings

Tips

• Save early, save often: The cost of saving is low. The cost of losing context is high.
• Restart > clear: /clear only clears history within the session. Restarting Claude Code gives a completely fresh context window.
• Front-load reading: Read all the files you'll need at the start of a task, before context fills up with working state.
• Use state files as TODO lists: "What's Next" in the state file doubles as your task list after restart.
• Checkpoint after breakthroughs: If you just figured out a tricky problem, save the insight immediately.