Beginner 3 min read

Context

Understanding Claude's working memory

Prerequisites

  • Basic Claude Code usage

What You'll Learn

  • Understand what context is and why it matters
  • Know what fills your context window
  • Use /compact, /clear, /cost commands
  • Optimize context for longer sessions
Claude's Context Window~200K tokensConversation HistoryUser: "Fix the login bug"Claude: "I'll investigate..."Files in Contextsrc/auth/login.tssrc/utils/session.tsTool ResultsGrep: 3 matches foundBash: Tests passedSystem InstructionsCLAUDE.md contentsProject conventionsCurrent Task: Everything Claude can "see" right nowContext = All the information Claude has access to in a conversation
01/05
0:00 / 0:26

Understanding Token Usage

Tokens are the units Claude uses to measure text. Roughly 1 token ≈ 4 characters or ¾ of a word.

Small File

~100 lines of code

~2,000 tokens

Medium File

~500 lines of code

~10,000 tokens

Large File

~2000 lines of code

~40,000 tokens

What Fills Your Context

System Prompt & Tools

~15-20%

Claude's base instructions and available tool definitions. This is always present.

Conversation History

~30-50%

All your messages and Claude's responses in the current session.

Files & Search Results

~20-40%

Contents of files you read, grep matches, and glob results.

Memory (CLAUDE.md)

~2-5%

Project and directory-level instructions loaded at session start.

Context Management Commands

/compact

Summarize the conversation to free up context space. Use when you get context warnings.

Tip: Auto-triggers when context gets very full

/clear

Clear all context and start completely fresh. Useful for unrelated tasks.

Tip: Warning: loses all conversation history

/cost

Show current token usage, costs, and context health.

Tip: Check periodically on long sessions

@filename

Reference a specific file to add it to context. Works in your messages.

Tip: Example: "Fix the bug in @src/auth/login.ts"

⚠️ When Context Gets Full

As your conversation grows, Claude automatically manages context to keep you productive:

Auto-Summarization

Older messages are condensed into brief summaries, preserving key decisions and context while freeing up space.

Context Pruning

Less relevant information (like old search results) may be dropped to make room for new, more relevant content.

You'll see a warning when context is getting full. Use /compact proactively to maintain quality.

Context vs Memory

Context (Session)

  • •Exists only during the current session
  • •Includes everything Claude can see now
  • •Limited by token window (~200K)
  • •Disappears when session ends

Memory (CLAUDE.md)

  • •Persists across all sessions
  • •Contains project instructions and preferences
  • •Stored in files on disk
  • •Loaded into context at session start

Memory (CLAUDE.md) is loaded into context each session. It's a way to give every session the same starting knowledge.

💡 Pro Tips

  • 1.Use /cost to check context usage before starting a large task—you might want to /compact first.
  • 2.Reference files with @filename instead of pasting contents—Claude will read exactly what it needs.
  • 3.For unrelated tasks, use /clear to start fresh rather than working with irrelevant context.
  • 4.Put persistent information in CLAUDE.md rather than repeating it—it's automatically included every session.
  • 5.Long sessions benefit from periodic /compact even before warnings appear.
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