Knock | Customer engagement infrastructure | WarmIndex

Knock is a developer-first customer engagement infrastructure platform that enables teams to build and manage cross-channel messaging experiences including in-app notifications, email, SMS, push, and chat.

🚀 Overview

Knock provides the infrastructure for product, marketing, and transactional messaging, allowing developers to activate their data and ship notifications across multiple channels without the limitations of traditional tools.

It solves the problem of fragmented notification systems where devs struggle with custom builds or rigid marketer-focused platforms, offering full control over design, data modeling, workflows, and delivery.

Built for engineering teams at SaaS companies like Vercel, Amplitude, Webflow, and Discogs, who need scalable, reliable messaging that integrates seamlessly into their stack.

We built it to empower developers with flexible, high-performance tools that respect user preferences and scale to hundreds of millions of messages monthly with 99.99% uptime.

✨ Key Features

Multi-channel messaging across in-app, email, SMS, push, chat with intelligent routing and personalization
Drag-and-drop workflow builder for complex journeys triggered by APIs, events, or segments
Data unification from warehouses, CDPs, reverse ETL; dynamic segmentation and custom objects
Developer tools including SDKs in all major languages, Knock CLI for AI IDEs/CI/CD, version control, observability
Optional: In-app guides for paywalls/nudges, AI agent functions, preference centers

🛠 Tech Stack

Frontend: React (@knocklabs/react components), Next.js examples
Backend: Elixir (core platform), Node.js SDK
Database: Integrates with PostgreSQL, data warehouses; Redis possible for caching
Auth: Custom API keys, Google SSO, SAML for Enterprise
Hosting: Cloud-based (Vercel customers suggest similar), enterprise dedicated infra

👥 Who Is This For?

This project is useful for:

Developers who want to build custom notification systems without starting from scratch
Teams looking for scalable cross-channel engagement infrastructure
Indie makers building SaaS products with user messaging needs

📸 Screenshots / Demo

Live demo: https://knock.app
GitHub: https://github.com/knocklabs (example apps: https://github.com/knocklabs/knock-node-example-app)

🔥 Project Status

🟢 Actively building

Last updated: 2026-03-24

❓ FAQ

Is this project free?

Freemium — Free Developer plan up to 10k messages/mo; Starter $250/mo for 50k; Enterprise custom. Usage-based overages.

Is the source code available?

Partially — Open-source client SDKs (JS, Node, React, Python, etc.) at https://github.com/knocklabs. Core platform is proprietary.

Can I contribute?

Yes — Contribute to SDKs and example apps via issues and PRs on GitHub (https://github.com/knocklabs). Feedback welcome via support.

📬 Contact & Links

Built with ❤️ and kept warm on WarmIndex.

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