Language
TypeScriptresend.com
Main language across the product, SDKs and React Email.
UI library
Reactbuiltin.com
Builds the interface and the email components.
Full-stack framework
Next.jsbuiltin.com
Framework for the web app.
Hosting
AWSresend.com
Main cloud, with serverless and container-based services.
Terraformbuiltin.com
Infrastructure as code, together with AWS CDK.
Database
PostgreSQLsupabase.com
Main database, hosted on Supabase.
Why: Supabase gave them Postgres and auth in one place so the team could move fast.
ClickHousebuiltin.com
Analytical database next to Postgres.
Login
Supabase Authsupabase.com
Signs in Resend's users, more than 300,000 of them by 2025.
Why: Bundled with the database, so they didn't need a separate auth tool.
React Emailgithub.com
Their own open-source library for writing emails as React components.
Why: They felt email development was stuck in 2010 and should work like modern web apps.
Build and runtime
Turborepogithub.com
Runs builds and tests in the React Email monorepo, with pnpm.
Backend framework
Node.jsresend.com
Runs the back-end services.
Used in the back end, including the MTA and sending systems.
Honobuiltin.com
Web framework for APIs, alongside Express.
Code quality
Biomegithub.com
Linting and formatting in the React Email repo.
Error monitoring
Datadogresend.com
Monitoring and observability for production.
Before Resend, the founders built React Email, a set of unstyled components for writing emails with React and TypeScript. Their argument: email development was stuck in 2010 and needed to work like modern web apps.
React Email is still open source and maintained by Resend, and it remains a core part of the developer tools team's work, alongside the SDKs, CLI and MCP server.
Sources:github.com resend.com
Resend came out of Y Combinator's Winter 2023 batch and picked Supabase for its database and auth. The reasoning: startups need to move fast, and Supabase gave them Postgres and authentication together, simple enough for two front-end engineers to handle.
It also had room to grow, with partitioning, read replicas and backups, and the YC credits meant they didn't worry about backend costs while looking for product-market fit. By 2025, more than 300,000 users signed in through Supabase Auth.
Sources:supabase.com ycombinator.com
Resend's current job posts describe a stack of TypeScript, Node.js, Go and Postgres running primarily on AWS, with infrastructure as code in Terraform or AWS CDK and monitoring in Datadog.
Earlier posts also listed Next.js, Express and Hono on the application side and ClickHouse next to Postgres for data.
Sources:resend.com resend.com builtin.com
Resend now has a team dedicated to MTA systems: SMTP delivery, routing, retries, backoff and IP pools. Engineers there work in TypeScript and Go.
Sources:resend.com
Found on the homepage with the open Wappalyzer rules (HTML, scripts and headers). It shows what runs in the browser, not the whole backend.
Checked on 2026-10-29. Every tool links to the public source that shows it.
