An open-source password manager publishes its client (and often server) code publicly, so independent researchers can inspect exactly how your data is encrypted — rather than taking a vendor’s word for it.
Why it matters for a password manager specifically
Password managers are a uniquely high-trust category: a flaw in the encryption implementation could expose everything at once. Public code review is one more layer of verification on top of a vendor’s own testing.
Open-source doesn’t mean unaudited
The strongest combination is open-source code plus regular independent professional audits — both boxes checked, not one instead of the other.
Our pick
Bitwarden is the only fully open-source option among the managers we’ve tested — client and server code are both public, alongside a regular audit cadence and an official self-hosting path. See our full open-source password manager list or the Bitwarden review.