No Backend, No Build Step: A Spaced-Repetition Chrome Extension That Runs on chrome.storage.sync Alone

Most "save this for later" tools I've used eventually want a server: an account system, a database for your notes, a sync service with its own outage history. I wanted something narrower — capture text or a whole page while browsing, turn it into a spaced-repetition flashcard, and have it show up on my other machine — without running any infrastructure at all. MindStack is a Manifest V3 Chrome extension that does exactly that: capture, spaced-repetition scheduling, a full dashboard, and cross-device sync, built entirely on chrome.storage.sync and chrome.identity . No backend, no bundler, no npm install before you can load it unpacked. Here's what that constraint forces you to get right. Decision 1: The scheduler is SM-2-shaped, not SM-2 Spaced repetition apps usually reach for a full SuperMemo SM-2 implementation — ease factors computed from response quality on a 0–5 scale, per-review interval history. MindStack's actual scheduler is a compressed version that captures the two properties that matter for a lightweight capture tool and drops the rest: const scoreReview = async ( score ) => { const memory = state . memories . find (( item ) => item . id === activeReviewId ); const interval = { forgot : 1 , hard : Math . max ( 1 , Math . round (( memory . reviewCount || 1 ) * 1.5 )), good : Math . max ( 2 , Math . round (( memory . reviewCount || 1 ) * ( memory . ease || 2.5 ))), easy : Math . max ( 4 , Math . round (( memory . reviewCount || 1 ) * (( memory . ease || 2.5 ) + 1 ))) }[ score ]; const updated = { ... memory , reviewCount : ( memory . reviewCount || 0 ) + 1 , successCount : ( memory . successCount || 0 ) + ( score === " forgot " ? 0 : 1 ), ease : Math . min ( 3.4 , Math . max ( 1.3 , ( memory . ease || 2.5 ) + ({ forgot : - 0.35 , hard : - 0.12 , good : 0.05 , easy : 0.16 }[ score ]) )), nextReviewAt : addDays ( interval ), }; Two properties, deliberately preserved from SM-2: intervals grow multiplicatively with review count (so a card you keep getting righ