Novu, Knock and Courier solve the same problem: your product needs to notify users across email, push, SMS and in-app, and you would rather not hand-roll the delivery logic. All three do that well. Picking between them comes down to three questions: do you need to self-host, how do you feel about per-event pricing, and who besides developers will ever touch the system? (If the category itself is new to you, start with our notification infrastructure guide and come back.)
At a glance
| Novu | Knock | Courier | Messy | |
|---|---|---|---|---|
| Open source | SDKs only | |||
| Self-hostable | ||||
| In-app inbox component | Chat widget | |||
| Workflow / digest engine | Drips | |||
| Marketer-facing campaigns | ||||
| Segments on customer attributes | ||||
| Shared inbox for replies | ||||
| Pricing basis | Events | Notifications | Notifications | Flat $20/mo or free self-hosted |
Pricing specifics shift too often to reprint here; all three run a free tier in the low tens of thousands of sends per month, with paid tiers that climb by volume. The structural point stands regardless of the current numbers: their bills track your send volume, so the price of a successful product launch is a pricing-page visit.
The three tools in detail
Novu: the open-source default
Novu is the biggest open-source name in the category, with a workflow engine, digest support and a polished in-app inbox. Self-hosting is real but not light: the stack wants MongoDB and Redis plus several services, so budget actual ops time. Choose Novu when open source is a requirement and your needs stop at delivering product notifications.
Knock: the polished SaaS
Knock is closed-source and cloud-only, and it uses that focus well: the workflow model (batching, throttling, preference sets, per-tenant overrides) is the most thought-through of the three. Choose Knock when you want the most capable managed option and self-hosting is not on your checklist.
Courier: the multi-provider veteran
Courier has been at this the longest and supports an enormous provider list behind one API, with a drag-and-drop template designer non-developers can operate. The core platform is SaaS; the open-source parts are SDKs and components around it. Choose Courier when provider breadth is the deciding factor.
The gap all three share
None of these tools knows who your customers are. They hold subscribers as delivery endpoints, not as profiles you can query. The consequence shows up about six months in, when marketing asks a reasonable question: "can we email everyone on the Pro plan who has not logged in for 30 days?" With a pure notification layer the answer is a SQL query, a CSV export and a second tool, and now two systems each hold half of every customer.
Concretely, the jobs that stay unsolved after adopting Novu, Knock or Courier:
- Broadcast campaigns picked and sent by a marketer, not an engineer
- Audience segments built on attributes and behavior
- Onboarding drips that react to what users do
- Anywhere for a customer's reply to land besides a dead no-reply inbox
When none of them is the answer
If those unsolved jobs are on your roadmap anyway, buying a notification layer first means buying a marketing tool second and writing sync code third. That stack (a delivery layer, Customer.io, and glue) is what Messy collapses into one product: the trigger-based send API developers want, plus campaigns, segments, drips and a shared inbox on the same customer record. Open source like Novu, full-stack like none of them.
The decision rule we would use ourselves: notifications only, self-hosted → Novu. Notifications only, managed → Knock or Courier. Notifications plus campaigns, support or lifecycle email anywhere in the next year → skip the glue-code phase and run something full-stack from day one.
