The Context Window and Why It Matters

What it means for the model to 'see' all your code at once and how that changes the way you work.

The Context Window is the most important concept to understand if you want to use Claude Code effectively. Put simply: it is the amount of text the model can 'see' at once while processing your request.

What Goes Into the Context Window

The Conversation

what you said and what it replied

Code Files

what you sent or it opened

CLAUDE.md

project instructions

Command Output

errors, logs, tests

What Happens When the Context Fills Up?

The model starts forgetting parts of the older conversation
Quality drops because the context becomes incomplete
The fix: start a new session and give it a short context
Claude Code warns you as it approaches the limit

Best Practice

Do not stretch one session across hours. Prefer several focused sessions. One clear, specific problem per session.