Context Optimization

Manage Claude Code's context window efficiently for faster responses, better memory, and productive long sessions.

Quick Reference

Command	Effect	When to Use
/compact	Compress context, preserve key info	Approaching limit, slow responses
/clear	Reset to empty context	Fresh start, topic change
/cost	Show token usage	Monitor consumption
/resume	Continue previous session	Multi-session workflows
/rename	Name current session	Session organization

Understanding Context

What Is Context?

Context is everything Claude "remembers" in your conversation:

• Your messages and Claude's responses
• Files read during the session
• Tool outputs (bash results, search results)
• System prompts and loaded skills

Context Window Limits

Model	Context Window	Practical Limit
Claude Opus 4.5	200K tokens	~150K usable
Claude Sonnet 4	200K tokens	~150K usable
Claude Haiku	200K tokens	~150K usable

Note: Reserve 20-30% for Claude's responses. Hitting the ceiling causes degraded performance before hard failures.

Token Estimation

Content Type	Approximate Tokens
1 line of code	10-15 tokens
100 lines of code	1,000-1,500 tokens
Typical source file	500-3,000 tokens
Large file (1000+ lines)	5,000-15,000 tokens
Your message	~1 token per word

Context Pressure Indicators

Visual Indicators

1. Token counter - Watch the usage bar in the UI header
2. Response time - Noticeably slower responses
3. Cost increase - Higher per-turn costs (use /cost)

Behavioral Signs

Sign	What's Happening
Claude "forgets" earlier discussion	Context truncation
Repeated questions about context	Information pushed out
Slower, choppier responses	Processing large context
Incomplete tool outputs	Context conservation
Asking to re-read files	File content evicted

When to Act

Usage Level	Recommendation
Under 50%	Continue normally
50-70%	Plan for compaction soon
70-85%	Compact now, consider task splitting
85%+	Compact immediately or clear

/compact - Context Compression

What /compact Does

1. Summarizes conversation history
2. Preserves key decisions and context
3. Maintains file awareness
4. Keeps recent changes tracked
5. Reduces token count by 50-80%

When to Use /compact

• Token usage exceeds 70%
• Responses becoming slow
• Before starting a new sub-task
• Transitioning between phases
• After completing a major task

Compact Workflow

> /compact

Claude compresses the conversation, keeping:

• Current task objectives
• Key decisions made
• Files modified/created
• Important constraints
• Recent context (last few turns)

Best Practices

1. Compact at natural breaks - Between tasks, not mid-implementation
2. State important context first - Mention critical info before compacting
3. Verify understanding after - Ask "What are we working on?" post-compact
4. Don't over-compact - Once per major phase, not every few turns

/clear - Fresh Start

What /clear Does

• Completely resets context to zero
• No memory of previous conversation
• Like starting a new session

When to Use /clear

Scenario	Why Clear
Switching projects	Different codebase, different context
Major topic change	Unrelated to previous work
Context too polluted	Too much irrelevant history
Starting fresh approach	Previous direction was wrong
Testing from scratch	Need clean state

/clear vs /compact

Aspect	/compact	/clear
Memory retained	Summarized	None
Token usage after	~20-50%	~0%
Context continuity	Preserved	Lost
Use case	Continue work	Fresh start

Clear Workflow

> /clear

Now starting fresh on [task description]...

Always restate your objective after clearing.

Context Budgeting

Planning Sessions

Before starting work, estimate context needs:

Task: Implement user authentication
Estimated reads: 10 files (~15,000 tokens)
Expected tool use: High (~20,000 tokens)
Conversation: Medium (~10,000 tokens)
Buffer: 20% (~10,000 tokens)
Total estimate: ~55,000 tokens (28% of window)

Budget Allocation Strategy

Category	Allocation	Notes
System prompt + skills	5-10%	Fixed overhead
File reads	20-40%	Be selective
Tool outputs	15-25%	Limit verbose output
Conversation	20-30%	Your messages + responses
Response buffer	20%	Room for Claude's output

Reducing Context Usage

1. Read selectively - Request specific functions, not entire files
2. Use targeted searches - grep patterns instead of reading files
3. Limit tool verbosity - Ask for summaries, not full outputs
4. Break into sessions - Split large tasks across multiple sessions
5. Use subagents - Delegate to separate context windows

Subagent Delegation

Why Subagents Help

Subagents have their own context window. Delegating tasks:

• Preserves main conversation context
• Allows parallel exploration
• Isolates experimental changes
• Returns only relevant results

Delegation Pattern

> Use a subagent to analyze the database schema and report the key tables

[Subagent runs in separate context]
[Returns summary to main conversation]

Good Candidates for Delegation

Task Type	Why Delegate
File exploration	Many reads, minimal output needed
Code analysis	Deep dive, summary sufficient
Test execution	Verbose output, pass/fail matters
Documentation reading	Large content, key points needed
Search tasks	Many grep/glob operations

Agent Definition for Context Efficiency

---
name: explorer
description: Explore codebase and return concise summaries
tools: Read, Glob, Grep
model: haiku
---

You are a code explorer. Investigate thoroughly but report concisely.
Return only essential findings. Summarize, don't quote entire files.

See creating-subagents for full agent creation guide.

Session Management

Naming Sessions

> /rename authentication-feature

Benefits:

• Easy to identify in history
• Clear purpose documentation
• Resumable with meaningful names

Resuming Sessions

> /resume

Shows recent sessions. Select one to continue where you left off.

Or directly:

> /resume authentication-feature

Multi-Session Workflows

For large features, plan multiple sessions:

Session	Focus	Compact At
Session 1	Architecture design	End
Session 2	Backend implementation	70%
Session 3	Frontend implementation	70%
Session 4	Integration & testing	End

Session Checkpoints

Create natural checkpoints:

1. Before major changes - Compact to preserve state
2. After milestones - Document progress in conversation
3. At decision points - State decisions clearly for post-compact memory

Efficient Workflows

Task Batching

Instead of interleaving tasks:

Inefficient:

> Read file A
> Make change to A
> Read file B
> Make change to B
> Read file A again

Efficient:

> Read files A and B
> Make all changes to A
> Make all changes to B

Explicit Context Statements

Help Claude remember across compactions:

> We're building a REST API for user management.
> Key constraint: Must use existing auth middleware.
> Files involved: src/api/users.ts, src/middleware/auth.ts

Pre-Compact Checklist

Before running /compact:

• Stated current objective clearly
• Mentioned key constraints
• Listed important files/decisions
• Completed current sub-task

Monitoring Usage

/cost Command

> /cost

Shows:

• Total tokens used
• Input vs output breakdown
• Estimated cost

When to Check

• After reading large files
• After verbose tool operations
• Every 10-15 exchanges
• Before starting new task

Reference Files

File	Contents
STRATEGIES.md	Detailed optimization strategies
INDICATORS.md	Context pressure indicators and monitoring
WORKFLOWS.md	Efficient workflow patterns

Quick Decisions

Situation	Action
Slow responses	/compact
Topic change	/clear
Large task ahead	Plan sessions, use subagents
Forgot earlier discussion	Restate context, consider clearing
Mid-implementation	Avoid compacting, finish first
Starting new feature	Name session, budget context