Strict runtime validation with Zod

In this episode, Gajus Kuizinas, co-founder and CTO of Contra, joins Aaron to talk about building the engineering world you want to live in, from strict runtime-validated SQL with Slonik to creating high-ownership engineering cultures. They dive into developer experience, runtime assertions, SafeQL, and even “Loom-driven development,” a powerful review process that lets teams move fast without breaking things.

Follow Gajus:
Twitter/X:  https://twitter.com/kuizinas
Slonk: https://github.com/gajus/slonik
Scaling article: https://gajus.medium.com/lessons-learned-scaling-postgresql-database-to-1-2bn-records-month-edc5449b3067

Follow Aaron:
Twitter/X:  https://twitter.com/aarondfrancis 
Database School: https://databaseschool.com
Database School YouTube Channel: https://www.youtube.com/@UCT3XN4RtcFhmrWl8tf_o49g  (Subscribe today)
LinkedIn: https://www.linkedin.com/in/aarondfrancis
Website: https://aaronfrancis.com - find articles, podcasts, courses, and more.

Chapters:
00:00 – Introduction
01:03 – Meet Gajus and Contra
01:48 – What Contra does and how it’s different
05:34 – Why Slonik exists & early career origins
07:47 – The early Node.js era and frustrations with ORMs
09:50 – SQL vs abstractions and the case for raw SQL
10:35 – Template tags and the breakthrough idea
12:03 – Strictness, catching errors early & data shape guarantees
13:37 – Runtime type checking, Zod, and performance debates
16:02 – SafeQL and real-time schema linting
17:01 – Synthesizing Slonik’s philosophy
21:29 – Handling drift, static types vs reality
22:52 – Defining schemas per-query & why it matters
27:59 – Integrating runtime types with large test suites
31:00 – Scaling the team and performance tradeoffs
33:41 – Runtime validation cost vs developer productivity
35:21 – Real drift examples from payments & external APIs
38:21 – User roles, data shape differences & edge cases
39:51 – Integration test safety & catching issues pre-deploy
40:52 – Contra’s engineering culture
41:47 – Why traditional PR reviews don’t scale
43:22 – Introducing Loom-Driven Development
45:12 – How looms transformed the review process
52:38 – Using GetDX to measure engineering friction
53:07 – How the team uses AI (Claude, etc.)
56:26 – Closing thoughts on DX and engineering philosophy
58:05 – Contra needs Postgres experts
59:00 – Where to find Gajus