I looked into it a bit. It stores memories near where it stores JSONL session history. It's per-project (and specific to the machine) Claude pretty aggressively and frequently writes stuff in there. It uses MEMORY.md as sort of the index, and will write out other files with other topics (linking to them from the main MEMORY.md) file.

It gives you a convenient way to say "remember this bug for me, we should fix tomorrow". I'll be playing around with it more for sure.

I asked Claude to give me a TLDR (condensed from its system prompt):

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Persistent directory at ~/.claude/projects/{project-path}/memory/, persists across conversations

MEMORY.md is always injected into the system prompt; truncated after 200 lines, so keep it concise

Separate topic files for detailed notes, linked from MEMORY.md What to record: problem constraints, strategies that worked/failed, lessons learned

Proactive: when I hit a common mistake, check memory first - if nothing there, write it down

Maintenance: update or remove memories that are wrong or outdated

Organization: by topic, not chronologically

Tools: use Write/Edit to update (so you always see the tool calls)