Can you highlight while offline? Local-first reality across 14 Read-Later apps — Slax ← Slax Blog Try a quick test

In 2019, Ink & Switch published Local-first software: You own your data, in spite of the cloud. At the end, it gave engineers a one-line tip:

“Test your app by turning off your WiFi, or using traffic shapers such as Chrome Dev Tools network condition simulator”

Turning off Wi-Fi is the simplest way to check whether an app is actually local-first.

We tried it on three Read-Later apps. Open the app, kill Wi-Fi, select some text, hit highlight:

Raindrop : you can apply the highlight, but it never saves — close the app, reopen it, and it’s gone.

Cubox : an error pops up.

Slax Reader : the highlight shows up, state is saved, no difference from online.

Different architecture, different result.

What is Local-first

The Ink & Switch paper lays out seven ideals:

#Original wordingOne-line meaning1No spinners: your work at your fingertips Instant response, no loading indicator2Your work is not trapped on one deviceSync across devices3The network is optionalNetwork is optional, not required4Seamless collaboration with your colleaguesReal-time collaboration5The Long NowStill works after the company is gone6Security and privacy by defaultEnd-to-end encryption by default7You retain ultimate ownership and controlData lives on your own device<br>The first ideal reads: “local-first software has the potential to respond near-instantaneously to user input, never needing to show you a spinner .” Not making users wait on a spinner is, literally, ideal number one.

The RxDB engineers later wrote The Local-First Future, and their headline image caption is “loading spinner not needed.” Spritle’s primer opens with a memorable image: “Imagine using your favorite productivity app at 30,000 feet — no internet, no loading spinners, no freezes.”

The product references are the same crowd: Figma, Linear, Notion, Obsidian, WhatsApp.

The highlight test: Offline-mode is not Local-first

Plenty of apps say “even offline” on their homepage. What it actually means hinges on one action:

When the network is gone, can you still highlight, comment, archive?

If you can only read what was already downloaded but can’t write anything new, that’s Offline-mode .

If everything happens, saves, and renders just like online, that’s Local-first .

The difference:

DimensionOffline-modeLocal-firstArchitectureClient-Server with a “snapshot download” patchLocal DB as primary storage; server is the sync layerWritesNeed networkLand locally, instantlyUser feelSpinner / error / disabled UINo waitCost to buildLowHigh<br>Offline-mode is a patch. Local-first is an architecture.

How 14 Read-Later apps actually stand

We went through 14 Read-Later / reader products serving Chinese and English audiences — homepages, docs, FAQs, changelogs — and verified their actual Local-first and Offline-mode support.

Of the 14, only Readwise Reader publicly and explicitly calls itself local-first.

ProductLocal-firstOffline-modeKey evidenceReadwise Reader✅ Yes✅ YesSite says “local-first web app ”; sync across devices “even offline”; offline full-text searchSlax Reader (this article)✅ Partial✅ YesHighlights / comments / likes / archive all land locally; offline feel matches onlineGoodLinks⚠️ Close, not claimed✅ YesiCloud Sync + rich-text local archive; offline reading; never claims local-firstInstapaper❌✅ YesSite: “You can read anything you save… even offline ”Matter❌✅ YesApp Store: “Available offline by default ”Wallabag❌✅ Yes (Android)Self-hosted; Android app caches images for offline readingCubox❌⚠️ PartialRecently-saved text auto-cached for offline reading; image cache and offline management “still being improved”Screvi❌✅ YesSite: “Read anywhere, even offline ”; mobile can download for offlineBeeMind⚠️ Scope unclear⚠️ Scope unclearSite says “local-first privacy” and offers “local model (for full offline privacy)”; no complete definitionRecall⚠️ Browsing only❌Site: “Augmented browsing is local first , your knowledge base is stored safely in the cloud”; offline mode still a user-voted feature requestRaindrop.io❌❌Official FAQ: “An internet connection is required to sync changes and save new bookmarks ”Karakeep❌❌Docs call themselves “self-hosting first”; “Offline reading on mobile” tagged Planned Noverload❌❌Its own comparison page assigns Offline reading to competitors, not itselfMarkwise❌❌Official blog: “No offline reading mode (yet) “Readless❌❌Cloud-based AI digest; no offline / local-first claims<br>A few facts from the table:

Of 14 products, 1 explicitly claims local-first (Readwise) and 1 effectively is but doesn’t say so (GoodLinks).

7 do snapshot-style offline reading — readable offline, not writable.

4 support neither, including the most popular one, Raindrop.

Wallabag and Karakeep are self-hosted: you can put the server in your own home, but a server is still a required middleman. Self-hosted is not Local-first.

Two reasons

Why are so few Read-Later...