See live Codex traces with the jsonl-viewer tool

Melvin Vivas · X post · 2026-09-15 · Open on X

Topics: AI Dev Tools & Productivity, AI Agents, Tool Use & MCP, Fine-tuning & Model Customization · Level: intermediate

Summary

The creator's open-source jsonl-viewer tool can show which Codex traces are live and running. The tool views and edits .jsonl files, which are often used for fine-tuning and training datasets. That makes it handy both for checking agent sessions and for working with datasets.

Key points

• jsonl-viewer is an open-source tool for viewing and editing .jsonl files.
• It can show which Codex session traces are live and still running.
• JSONL is a common format for fine-tuning and training datasets, so the same tool helps you check that data.

Resources mentioned

• donvito/jsonl-viewer · repo · github.com · free
  Open-source tool for viewing and editing .jsonl files (fine-tuning datasets) and agent traces from Codex, Claude Code, Pi and Hermes.
  Also in: jsonl-viewer: Live Traces for Codex Orchestrator and Subagents (Melvin Vivas on X · notes), Melvin Vivas's open-source AI tools, built with Codex (Melvin Vivas on X · notes), Analyzing Codex Traces with jsonl-viewer (Melvin Vivas on X · notes), jsonl-viewer: Inspect Coding Agent Traces (Codex, Claude Code, Pi, Hermes) (Melvin Vivas on X · notes) and 12 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

Try this

• Use jsonl-viewer to watch your Codex traces or to check JSONL fine-tuning datasets.