How to Write TypeScript with Codex - Neel Rao, OpenAI

Description

OpenAI's Codex is an AI coding assistant that helps developers write code faster and smarter. In this talk, Neel Rao from OpenAI shares how to use Codex for TypeScript projects. Learn how to write TypeScript code that works better with Codex, and how to structure codebases to boost its performance. Neel explains why smaller, focused files and strong end-to-end typing matter. He also shows how to auto-generate typed API clients to make contracts clear for Codex. Beyond coding tips, Neil discusses incremental development, test-driven workflows, and managing Codex-generated pull requests. If you want to level up your TypeScript with AI, this talk is packed with practical insights. Neel Rao is a Software Engineer at OpenAI, where he builds internal tools for trust and safety on the Intelligence and Investigations team. He previously co-founded GameSnacks (CTO, 2018–2022) and Advr (Co-founder/CTO, 2016–2018). Neel has also worked at Google and studied at UC Berkeley. OpenAI is an AI research and deployment company with a mission to ensure artificial general intelligence benefits all of humanity. OpenAI developed ChatGPT, GPT-4, DALL-E, Codex, and other AI models and products. 🔗 CONNECT WITH NEEL RAO LinkedIn: https://www.linkedin.com/in/neel-rao-41797154 OpenAI: https://openai.com 📚 MASTRA RESOURCES Mastra: https://mastra.ai Learn Mastra in the world's first MCP-Based Course: https://mastra.ai/course Principles of Building AI Agents (Book): https://mastra.ai/book Patterns for Building AI Agents (New Book): https://mastra.ai/blog/patterns-book https://docs.google.com/forms/d/e/1FAIpQLSduJjc515f6RZJqtkR2ByqJZrB0iP8B7SUKnjjZE9IajH_I8w/viewform The TypeScript AI conference is the first conference for TypeScript AI developers. The inaugural event took place on November 6, 2025, in San Francisco and online. MASTRA? Mastra is an open-source TypeScript framework designed for building and shipping AI-powered applications and agents with minimal friction. It supports the full lifecycle of agent development—from prototype to production. You can integrate it with frontend and backend stacks (e.g., React, Next.js, Node) or run agents as standalone services. If you’re a JavaScript or TypeScript developer looking to build an agentic or AI-powered product without starting from first principles, Mastra provides the scaffolding, tools, and integrations to accelerate that process. 00:00 Introduction and Speaker Background 00:46 Practical Tips for Using Codex 01:07 Structuring Codebases for Codex 02:58 Using Codex for Design and Planning 03:36 TypeScript-Specific Advice: Types for Everything 05:02 Auto-Generating Typed API Clients 06:10 When to Use Codex for Small Fixes 08:02 Recommended Prompting Workflow: Incremental Development 09:50 Using Codex to Learn and Understand Codebases 10:22 Testing and Reviewing Code with Codex 11:40 Managing PRs Generated by Codex 14:11 Limitations and Differences of Codex in the Browser 15:14 How to Prompt Codex Differently from Other LLMs 16:33 Using Versions and Multiple Codex Responses 17:11 Future of Codex and AI Coding Tools 18:41 Using MCP Tools and Context Engineering with Codex 20:25 Measuring Codex Performance and Evals 23:07 How OpenAI Engineers Maximize Codex in Their Workflow