Add Custom Compaction Instructions to Preserve Key Context

When Claude Code compacts your conversation (either automatically or via /compact), it summarises everything to free up context space. But the default summary might drop details you care about, like specific test output or API response formats.

You can tell Claude exactly what to prioritise:

> /compact Focus on code samples, test failures, and API response shapes

The text after /compact becomes the summarisation instruction. Claude will weight those areas more heavily when deciding what to keep and what to drop.

For project-wide defaults, add compaction instructions to your CLAUDE.md:

# Compact instructions

When you are using compact, please focus on:
- Test output and failure messages
- Code changes and their rationale
- API contracts and type signatures
- File paths that were modified

This way, every automatic compaction in this project preserves the context that matters most to your workflow.

This is especially useful for long debugging sessions where you need Claude to remember specific error messages and stack traces, or for refactoring sessions where the sequence of changes matters.

Don't let auto-compaction throw away the context you actually need.

via Claude Code Docs — Costs