Codex Thread Inspector

Visualize Codex agent session internals — timeline, token usage, tool calls, and context layers.

Built for a deeper look at what happens inside Codex agent sessions. Parses the JSONL rollout files that Codex writes to ~/.codex/sessions/ and renders them as an interactive web UI.

Quick Start

git clone https://github.com/jarrodwatts/codex-thread-inspector.git
cd codex-thread-inspector
pnpm install
pnpm dev

Opens a local dev server at http://localhost:3000 with your Codex sessions auto-discovered.

No Codex installed? You can also drag-and-drop any .jsonl rollout file directly into the upload zone.

Features

• Session timeline — Every turn, tool call, and context event in chronological order
• Token panel — Cache rates, per-turn token breakdown, cumulative usage chart
• Context layers — See system prompts, developer instructions, and turn context as the model sees them
• Search — Filter turns and tool calls by keyword
• Upload mode — Inspect any rollout file without Codex installed

Requirements

• Node.js 18+
• pnpm
• Codex CLI (for auto-discovery of sessions) — or use upload mode without it

How It Works

Codex writes a JSONL rollout file for each session to ~/.codex/sessions/YYYY/MM/DD/rollout-{id}.jsonl. Thread Inspector parses these files and builds a view model with:

• Session metadata (model, branch, working directory)
• Turn-by-turn timeline with tool calls and responses
• Token statistics with input/output/cache breakdowns
• Context events (compactions, developer instructions, system prompts)

License

MIT