Building a Jev Session-History Tool with Codex and Astra

Melvin Vivas · X post · 2026-09-29 · Open on X

Topics: AI Dev Tools & Productivity, Portfolio Projects · Level: intermediate

Summary

The creator is building a tool for Typesafe AI's Jev that keeps a history of Jev sessions and lets you run experiments. He built it with the AI coding tools Codex and Astra. The finished tool became the JevDev repo.

Key points

• Goal of the tool: save a history of Jev sessions and run experiments on them.
• It was built with Codex and Astra.
• Jev comes from Typesafe AI (@typesafeai on X).
• The creator later published it as github.com/donvito/jev-dev.

Resources mentioned

• TypeSafe AI (@typesafeai) on X · person · x.com · free
  The X account of TypeSafe AI, the company that makes Jev and the System One models.
  Also in: Using Jev (TypeSafe AI) as a Decision Model for Email Classification (Melvin Vivas on X · notes), Not every problem needs an LLM: small fine-tuned models (Jev by TypeSafe AI) (Melvin Vivas on X · notes), Jev model added to the AIBackends API via Vercel AI Gateway (Melvin Vivas on X · notes), AIBackends: An API Layer Between Your App and AI Models (Now with Jev) (Melvin Vivas on X · notes) and 6 more
• Jev (TypeSafe AI) · tool · typesafe.ai · free
  TypeSafe's new post-training algorithm for calibrated, confidence-scored decisions, pitched as a replacement for RLHF.
  Also in: JevDev: Open-Source UI Tool for Experimenting with Jev (Typesafe.ai) (Melvin Vivas on X · notes), jev-dev: A UI Tool to Keep Run History When Experimenting with Jev (Melvin Vivas on X · notes), JevDev: Open-Source UI for Experimenting with Jev by Typesafe.ai (Melvin Vivas on X · notes), Model Routing: Fine-Tune Your Own Router on Your Prompts (Melvin Vivas on X · notes) and 7 more
• OpenAI Codex · tool · openai.com · paid
  OpenAI's coding agent. In the diagram it writes code, fixes review findings and drives the build loop. The creator also used it to make this video.
  Also in: An agent bot that installs and drives Codex on its own (Melvin Vivas on X · notes), Asking a Coder bot to install Codex (Melvin Vivas on X · notes), Sign in with ChatGPT: Setting Usage Limits for Each App (Melvin Vivas on X · notes), Codex Cloud Environments Must Be Saved & Published Before Use (Melvin Vivas on X · notes) and 240 more
• GPT-6 Astra · tool · openai.com · paid
  The model announced in the quoted launch post, pitched as the developer's most capable model for work, coding, science and cybersecurity, and able to operate a computer.
  Also in: Customizing Your Coding Setup with Pi Coding Agent Extensions (Melvin Vivas on X · notes), Pi Agent Council: Ask Multiple LLMs in Parallel and Compare Their Advice (Melvin Vivas on X · notes), Use GPT-6.1 Sol by Default, Save Astra for Emergencies (Melvin Vivas on X · notes), Dots in ChatGPT: always-on AI agents that you hand responsibilities to (Melvin Vivas on X · notes) and 49 more

Try this

• Build a tool that records the history of AI tool sessions and lets you run experiments on them.