Inventory sync software exists to do one thing: when a unit sells anywhere, every other channel learns before it can sell the same unit. That makes the category unusually easy to rank honestly, there is one decisive spec, propagation speed, and vendors either document it or hide it. This roundup ranks by the documented number, sourced from each vendor’s own pricing pages and help centers (July 2026). Disclosure up front: Unifystock is our product; the receipts below are checkable, and the afternoon test settles anything.
The cadence table, documented claims only
| Tool | Documented propagation | Source class | Pricing shape |
|---|---|---|---|
| Unifystock | Under 3 seconds, event-driven | Published spec | From $49/mo flat, unlimited orders |
| StoreAutomator | ~15 min quantities, ~4 min Amazon, hourly data | Their docs | Quote-only |
| Zentail | Feeds every 15 min (Shopify re-verify 24h) | Their help center | From $300/mo, annual only |
| Sellbrite | 15 minutes on paid plans | Their materials | $29-$179 order tiers |
| LitCommerce | 15 minutes (inventory, price, orders) | Their pricing table | From $29/mo, listing quotas |
| Koongo | 5 / 15 / 60 minutes by plan | Their pricing | From EUR 24 |
| Salestio | Real-time on Scale+ only; 15-30 min below | Their pricing | Free-$299 + per-order overage |
| ExportYourStore | “2 hours or less” | Their own number | $29-$249, listing caps |
| Listing Mirror, GeekSeller, M2E, SellerActive | “Real-time / near real-time”, no interval documented | Marketing copy only | Various |
Three readings of that table. First, honesty varies more than speed: the vendors who publish 15 minutes deserve credit over the ones who publish adjectives. Second, the paywalled-cadence model exists: Salestio sells real-time as a tier, your sync speed is a pricing lever there. Third, an undocumented cadence is a finding: assume polling on an interval until shown otherwise, the architecture divide explained.
Why the number is the product
The oversell window equals the propagation delay: two channels can sell the same last unit for exactly as long as they disagree about it. At 15 minutes, thin fast SKUs double-sell weekly; at two hours, the dropship-grade lag, it is a business model constraint; at seconds, the window rounds to closed, the full oversell mechanics and what cancellations cost on each marketplace. Every other feature, listings, rules, forecasts, sits on top of this number, which is why it belongs in the first question you ask a vendor, not the last.
Picks by situation
Thin stock, fast movers, or one-of-a-kind pieces: event-driven only. Unifystock is built as exactly that, a sale fires the update, under 3 seconds across every channel you connect (six native: Amazon, eBay, Etsy, Shopify, WooCommerce, OpenCart), with buffers as the second seatbelt, on published tiers from $49 that never meter orders.
Deep stock, slow velocity, EU feed channels: Koongo’s intervals may genuinely suffice, its bol/Zalando/Kaufland depth is real, the read, buffer accordingly.
Amazon/eBay/Etsy only, low volume, budget-first: Salestio below the real-time tier, with eyes open that your cadence is 15-30 minutes until the $199 plan, the analysis.
Mid-market US on annual contracts: Zentail’s 15-minute feeds are honest and consistent, the details, the floor is the price, not the sync.
Common questions
Is 15 minutes actually bad?
It is a known, priceable risk: fine at depth-of-stock 50, expensive at depth 1-3 with real velocity. Size buffers to the interval if you run one.
How do I verify a vendor’s claim?
Two channels, one test SKU at quantity 1, buy it on channel A, stopwatch channel B, the full protocol. Twenty minutes, no marketing survives it.
What does event-driven mean technically?
The platform pushes a sale notification the moment it happens (webhook or plugin event) instead of the tool asking on a timer, the integration-method guide.
Why do so many vendors hide the number?
Because polling architectures are cheap to run and unimpressive to print. Treat the silence as the spec sheet, the candor test.
The number, on the page
Under 3 seconds, event-driven, six native channels, unlimited orders on every plan, from $49/month. See pricing.