Resend for SMS. SMS DEV is a free, open-source SMS development tool that lets you build & test messaging apps with zero costs. Beautiful web UI and works with any stack. Built by the Relay team for the soon-to-be launched Relay SMS stack. No number provisioning, no Twilio. Simple local SMS development tools.

Hey PH! I built SMS DEV after getting stuck in a testing loop with Twilio and burning through credits. I started out making a better SMS dev tool and while that's still in development, that I'd ship this little app. Every developer I talked to had the same story - expensive testing, complex setups, and teams juggling multiple phone numbers. What makes SMS DEV unique? Unlike other SMS testing tools that focus on just sending messages, SMS-dev creates a complete local SMS environment. You get a web UI for managing conversations, full webhook simulation, and it's drop-in compatible with the soon-to-be launched Relay API - so switching between dev and production will be seamless. What I'm most proud of? The bundled architecture. Getting a full Next.js UI to bundle directly into a CLI tool was technically challenging (for me) but it means devs can get a rich web interface with zero configuration. No separate servers, no complex setup - just npm install and you're testing SMS flows. The testing response has been incredible. It's being used by the engineering team I lead at UM. Try it out and let me know what you think. Dan