The notification layer for modern software - one API for in-app, email, SMS, push and chat.
KNOCK, NEW YORK — The quiet infrastructure moving hundreds of millions of messages a month for companies that decided not to build their own.
Every engineering team eventually builds a notification system. Preferences, digests, quiet hours, five channels, localization, an on-call page at 2am. Knock's argument is simple: this is real infrastructure, and infrastructure should be rented, not rebuilt.
Founded in New York in 2021 by Sam Seely and Chris Bell - who lived the problem as product and engineering leaders at Frame.io before its acquisition by Adobe - Knock gives developers a single API, dashboard, and set of SDKs to design and deliver messages across in-app feeds, email, SMS, push, and chat tools like Slack and Microsoft Teams. Instead of stitching together Twilio, SendGrid, and Firebase and then maintaining the glue forever, teams describe a workflow once and let Knock route, batch, and deliver it.
The pitch resonates because it is almost self-fulfilling: you will build this feature anyway, probably more than once, and probably badly the first time. Knock sells the version that already handles the hard parts - user preferences, batching, deduplication, compliance, and observability - and does it behind a 99.99% uptime SLA.
"Customers such as Amplitude, Vercel, and Webflow use Knock to power customer messaging without needing to build, maintain, and scale their own in-house notification system."
At its core, Knock is a workflow engine wrapped in a developer-friendly API. Teams design notification logic - conditions, delays, branches, batching - visually or in code, then trigger it with a single call. Knock fans that trigger out to every channel a user has opted into, respecting their preferences and quiet hours.
Around that engine sits a full toolkit: prebuilt in-app feed components, managed preference centers, content localization, audit logs, and cross-channel analytics. For developers there is a CLI, CI/CD integration, version control for workflows, and SDKs for Node, Python, Ruby, Go, Java, .NET, Elixir, and PHP.
Knock sells to developer, product, and engineering teams at software companies - the people who would otherwise own a home-grown notification service. More than 200 enterprises run on it today.
Design cross-channel notification logic - batching, delays, conditions, branching - without custom code.Since 2021
One integration ships to in-app, email, SMS, push, chat, Slack and Microsoft Teams.Since 2021
Prebuilt UI components and SDKs to embed real-time notification inboxes in web and mobile.Since 2022
Managed preference centers, per-user channel controls, quiet hours, and content localization.Since 2022
CLI, CI/CD, version control for workflows, and SDKs across eight-plus languages.Since 2022
Built-in logs, audit trails, and cross-channel analytics with Datadog, New Relic and Segment.Since 2023
Natural-language workflow generation and a local MCP server with human-in-the-loop approval.Since 2025
SAML 2.0 SSO, role-based access, and HIPAA, SOC2, GDPR & CCPA compliance out of the box.Enterprise
Notifications look trivial until you ship them. Then come the edge cases: which channel, at what time, in what language, batched or immediate, and only if the user hasn't muted you. Get it wrong and users tune out or churn. Building all of that in-house consumes months of engineering time on a system that is never the company's actual product.
Notifications are ultimately a trust problem disguised as an engineering problem. Knock gives teams the controls - preferences, workflows, analytics - to earn attention rather than burn it.
The common alternative is a home-grown system built on raw providers like Twilio, SendGrid, and Firebase - cheap to start, expensive to maintain. On the vendor side, Knock competes with Courier, Novu, MagicBell, OneSignal, and engagement suites like Braze and Customer.io.
Knock's wedge is developer-first depth: version-controlled workflows, a real CLI, SDKs in eight-plus languages, and an infrastructure posture - 99.99% uptime and enterprise compliance - aimed at teams that treat messaging like code.
Knock runs a B2B SaaS / usage-based model: subscription and usage pricing on its notification API, a free developer tier, and enterprise plans adding SSO, security, and compliance. It has raised about $18M to date.
The 2024 Series A was led by Craft Ventures, with existing backers Afore Capital and Preface Capital joining. Craft co-founder David Sacks took a board seat - a bet that unglamorous infrastructure, the kind that quietly powers everyone else's product, is where durable software businesses get built.
Sam Seely and Chris Bell, former Frame.io leaders, start Knock to fix the notification problem they lived firsthand.
A previously undisclosed seed led by Afore Capital funds the first version of the notification API.
In-app feeds, preference management, and SDKs across major languages ship.
Craft Ventures leads; David Sacks joins the board and total funding reaches $18M.
AI workflow generation, an agent toolkit, and a local MCP server bring machine-sent messaging under human control.
Co-Founder & CEO. Former product leader at Frame.io, where he first hit the notification problem Knock now solves.CEO
Co-Founder & CTO. Former engineering leader at Frame.io; architects Knock's delivery infrastructure.CTO
The team of roughly 28 works developer-first and remote-friendly, shipping modern tooling on a stack that spans Elixir, Rust, TypeScript, Kubernetes, and AWS.
Knock is notification and customer-engagement infrastructure. It gives developers a single API, dashboard, and set of SDKs to build and deliver messages across in-app, email, SMS, push, and chat channels without building an in-house system.
Knock was founded in 2021 by Sam Seely (CEO) and Chris Bell (CTO), who previously worked together on the product and engineering side at Frame.io.
About $18M total, including a $6M seed led by Afore Capital and a $12M Series A led by Craft Ventures announced in February 2024.
More than 200 enterprises, including Vercel, Webflow, Amplitude, Clay, Medium, Gorgias, and Outreach, collectively delivering hundreds of millions of messages per month.
Knock replaces months of engineering - workflows, preferences, batching, localization, multi-channel delivery, and compliance - with a managed platform offering a 99.99% uptime SLA and HIPAA, SOC2, GDPR, and CCPA compliance.