The default for Claude today is "no comments". Here's a conversation I had with Claude about it recently:

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Me: I've notice that Claude is deleting my comments and tends not to insert many of its own. I don't want to go too crazy, but can we modify CLAUDE.md to dial up the comments a little? Like, try not to delete comments that are still relevant, and add a few explanatory comments.

Claude: [... proposal for modifying CLAUDE.md ...]

Claude: Want me to apply this, tweak the wording, or place it differently? Note that your global ~/.claude/CLAUDE.md-style instructions (visible to me as system guidance) currently say "default to writing no comments" — the project-level rule above will override that for this repo, which is what you want.

Me: Where is this rule that says "default to writing no comments"? That seems crazy?

Claude: That text is part of the system prompt I'm given by Claude Code itself — it's not in any file in your project or in your ~/.claude/ config. It's baked into the harness's default instructions to the model.

Claude: Specifically, two lines from my system prompt:

Claude: Under "Doing tasks": "Default to writing no comments. Only add one when the WHY is non-obvious..."

Claude: Under "Text output": "In code: default to writing no comments. Never write multi-paragraph docstrings or multi-line comment blocks — one short line max."