The short answer

Local-first software is built so your data and its working copy live on your own disk by default, with the application fully usable with no network connection at all — rather than a cloud service that happens to cache something locally for when the connection drops.

The distinction is about which copy is the real one. A cloud-first app treats the server as the source of truth and your device as a client of it. A local-first app treats the file on your disk as the source of truth, whether or not a network exists at all.

What that changes in practice

A few consequences follow directly from where the real copy lives:

• No account is required to use the app, because there's no server-side record for an account to attach to.
• The app keeps working if a company stops running its servers, because it was never depending on them to begin with.
• Backing up the disk backs up the software's data, without a separate export step, because there's nothing living anywhere else to export.
• Moving to a new machine means moving a folder, not requesting a data transfer from a service.

None of this rules out syncing between two of your own machines — it just means syncing happens through something you already trust with your files (a synced folder, an external drive) rather than through an account the software manages on your behalf.

The trade it makes

The thing given up in exchange is anything that genuinely needs a server: a shared workspace two people edit at once, a public link that shows a board to someone with no copy of the app, or a search that reaches into a model too large to ship inside the application itself. Local-first software can still do some of these — syncing a folder between two of your own Macs, for instance — but it does them by relying on infrastructure you already chose for another reason, rather than infrastructure the app installs a dependency on.

Where reference tools land on this

The category splits roughly the way most creative software does. Coii Ref keeps its database, thumbnails and canvases inside the folder you point it at, makes exactly two kinds of outbound request — a licence check on activation and a launch-time read of a Date header — and needs no account to run at all, trial or paid. refern takes a similar local-first stance on the workspace itself while still offering optional network-dependent features like its on-device tagger's component downloads, which is a different trade worth reading in full before assuming either app is "the" local-first option in this category.

If a library that survives a dead server, a lapsed subscription or a machine with no internet connection at all is the actual requirement, an organizer that never moves your files and an offline moodboard app with no account both start from that same premise. Or try Coii Ref — thirty days, no card, no account to create in the first place.