# I built a local-first tab manager and gave it an MCP server so Claude can organize my tabs > Source: > Published: 2026-08-14 23:57:41+00:00 I'm a designer and developer, and a hopeless tab hoarder. On a normal day I've got 70+ tabs open across a couple of windows, every favicon crushed into an unreadable sliver, and my "system" for finding anything is to just… open another tab. Bookmarks? A write-only graveyard I never revisit. I bounced between tab managers for a while. Toby was the one that stuck — until it capped the free plan at 60 saved tabs and started asking for an account. For a tab hoarder, a 60-tab cap is like a notes app that locks after 60 words. That was the nudge. So I did the reasonable thing and spent way too long building my own. It's called **Mos Tab**. This is the build story — the parts I'm proud of, the part that nearly broke me (multiple windows, I'm looking at you), and the weirdly fun part at the end where I let Claude reorganize my tabs. Three non-negotiables: Mos Tab overrides `chrome://newtab` (MV3). The data model is a boring normalized tree — **Space → Collection → Section → Tab** — records plus ID arrays for ordering. It's a single Zustand store with a `persist` middleware writing to `chrome.storage.local` . Your currently-open tabs show in a live side panel (`chrome.tabs` ); one click saves them into a collection, drag to organize, and a `cmdk` palette searches everything you've saved. Stack, for the curious: React 18 + TypeScript + Vite + `@crxjs/vite-plugin` , Tailwind, dnd-kit, zod, i18next (5 languages). Since the new tab is prime real estate, I threw in the stuff I open a tab for anyway — calendar, pomodoro, to-dos, sticky notes. All free. So far, so normal. Then I wanted sync. Local-first is lovely until you have two machines. I wanted **optional** cloud sync (the paid tier — more on money later) without turning this into a database migration. The backend is deliberately dumb: a **Cloudflare Worker + R2**, one JSON blob per user (`state.json` ). No per-row DB. To save, you `PUT` the blob back with an **ETag conditional request** (`If-Match` ). On a `412` (someone wrote first), you pull, **3-way merge** on the client, and push again. The 3-way merge (base + local + remote) handles the real cases: both sides added a tab → keep both; something in `base` vanished on one side → it was deleted, respect it; field conflicts → local wins. Sticky-note text conflicts resolve to a *symmetric* content-addressed copy, so two machines converge instead of endlessly duplicating. The part that actually broke me wasn't cross-device — it was **multiple windows on the same machine.** Every window wanted to push, each invalidating the others' ETag → 412 → merge → push → 412 → forever. A beautiful infinite loop. The fix: **only the focused window pushes.** Every window can pull (reads are idempotent), but writes are gated to the focused one, with a flush-on-blur so the last edit isn't lost when you switch away. Add adaptive polling backoff (15s active → 2min idle) and an "away mode" that stops polling after 20 min of no activity, and it stops hammering the Worker. Here's the part I'm actually excited about. I gave Mos Tab a remote **MCP server** so you can connect Claude or ChatGPT to it. Once connected, the assistant can search and summarize everything you've saved (tabs, notes, to-dos) and — the fun bit — **save new things it finds into a brand-new space**, add notes, or make a public share link. All from the chat. Concrete example. I told Claude: "Find the top-rated budget strollers on Amazon, save them to my tabs, and make a share link." A few seconds later there was a new "Stroller shortlist" space on my dashboard, organized into categories, and a public link I sent straight to my wife — she opened it in her browser, nothing to install. Two design decisions I'm happy with: `fetch` Worker — no Durable Objects, no McpAgent. Auth is a long-lived scoped token you mint in settings (JWTs expire, which is bad for a persistent connection). Reads filter the same per-user blob in memory; writes are read-modify-write with `If-Match` / 412 retry — so an AI-created space merges through the That last bit is the thing I like most: AI writes go through the same door as everything else. No special path, no separate store. Because someone always asks: the whole local app is free — unlimited tabs, spaces, all the widgets, import/export. **Local storage costs me nothing to run, so there's no reason to cap it.** The paid tier is only the stuff that actually hits a server: multi-device sync, public sharing, and the AI/MCP integration. I can't give the server stuff away free — kind of wish I could. That's the whole pricing philosophy, and it keeps me honest. Live on the Chrome Web Store (Chrome + Chromium — Edge, Brave, Arc, etc.): I'm a solo dev, so I read everything — feedback on the sync merge model or the MCP design especially welcome.