Inspecting Coding-Agent Traces Live with JSONL Viewer (Codex, Claude Code)

Melvin Vivas · X video post · 2026-09-07 · 0:21 · 763 views · Open on X

Topics: AI Agents, Tool Use & MCP, AI Dev Tools & Productivity, LLMOps, Deployment & Monitoring · Level: intermediate

Summary

This short post (a silent video) shows JSONL Viewer v1.3.2, a tool that streams the session trace files (JSONL logs) written by coding agents like Codex, Claude Code, Pi and Hermes and displays them live. The point is observability: Codex's UI doesn't show detailed activity, but its trace logs do. Reading these traces lets you see each step, tool call and message the agent makes behind the scenes.

Key points

• Coding agents such as Codex, Claude Code, Pi and Hermes record their sessions as JSONL trace files (one JSON event per line).
• Codex's UI hides detailed activity, so reading its raw traces is the way to see what it is actually doing.
• JSONL Viewer v1.3.2 added live streaming of trace views, so you can watch an agent's steps as they happen, not only after the run.
• Supported agents in v1.3.2: Codex, Claude Code, Pi and Hermes.
• Use cases: understanding agent loops, debugging unexpected behavior, and seeing which tool calls the agent makes.

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), See live Codex traces with the jsonl-viewer tool (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) 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
• Claude Code · tool · code.claude.com · paid · recommended by both Bashiri Smith & Melvin Vivas
  Build agents and pipelines from the terminal; the guide's main agentic coding tool.
  Also in: Create Claude Code Plugins with /plugin-authoring (Melvin Vivas on X · notes), Claude Code mods: customize behavior and UI with plugins (Melvin Vivas on X · notes), AI Engineer Roadmap Overview: From ML Foundations to RAG, Agents & Ops (Bashiri Smith on Facebook · notes), SkillsBento: Free Plugin Marketplace for Codex and Claude Code (Melvin Vivas on X · notes) and 101 more
• Pi · tool · x.com · free
  A customizable coding agent that can be extended through its Extensions API and connected to several model providers.
  Also in: Sign in with ChatGPT: Setting Usage Limits for Each App (Melvin Vivas on X · notes), Pi reaches v1.0 (Melvin Vivas on X · notes), Claude Code mods: customize behavior and UI with plugins (Melvin Vivas on X · notes), Customizing Your Coding Setup with Pi Coding Agent Extensions (Melvin Vivas on X · notes) and 39 more
• Hermes Agent · tool · github.com · free
  Nous Research's open-source AI agent with CLI, TUI and desktop interfaces. It now supports hands-free activation with a wake word.
  Also in: Hermes Agent: each bot is its own profile (Melvin Vivas on X · notes), An X research bot built with Hermes (Melvin Vivas on X · notes), Run Your Hermes Agent on Free LFM2.5-2.6B via OpenRouter (Melvin Vivas on X · notes), Running a Local Ornith Model as the Backend for a Hermes Agent (Melvin Vivas on X · notes) and 55 more

Try this

• Install JSONL Viewer from the donvito/jsonl-viewer GitHub repo.
• Open the live trace of a Codex or Claude Code session and follow the agent's steps and tool calls as they happen.