Rendering

go-session provides two output formats for visualising parsed sessions: a self-contained HTML timeline and an MP4 video rendered via Charmbracelet VHS.

HTML Timeline

RenderHTML generates a single HTML file with no external dependencies. The output includes:

Sticky header with session ID, start time, duration, tool call count, and error count
Search bar with real-time filtering (press / to focus)
Type filter dropdown: All events, Tool calls only, Errors only, Bash only, User messages
Collapsible event cards colour-coded by tool type:
- Green: Bash commands
- Blue (accent): Other tools (Read, Edit, Write, Grep, Glob)
- Yellow: User messages
- Grey: Assistant responses
- Red border: Failed tool calls

Usage

sess, err := session.ParseTranscript("session.jsonl")
if err != nil {
    log.Fatal(err)
}

if err := session.RenderHTML(sess, "output/timeline.html"); err != nil {
    log.Fatal(err)
}
// Open output/timeline.html in any browser

Event Card Layout

Each card displays:

Element	Description
Timestamp	`HH:MM:SS` of the event
Tool badge	Colour-coded tool name
Input summary	Truncated to 120 characters
Duration	Formatted as ms/s/min/hr
Status icon	Green tick or red cross for tool calls

Clicking a card expands it to show the full input (labelled contextually as Command, Message, File, or Target) and the complete output.

Labels

The input label adapts to the tool type:

Bash: "Command"
Read, Glob, Grep: "Target"
Edit, Write: "File"
User messages: "Message"
Assistant: "Response"

MP4 Video

RenderMP4 generates a terminal recording using VHS. VHS must be installed separately.

Prerequisites

go install github.com/charmbracelet/vhs@latest

Usage

sess, err := session.ParseTranscript("session.jsonl")
if err != nil {
    log.Fatal(err)
}

if err := session.RenderMP4(sess, "output/session.mp4"); err != nil {
    log.Fatal(err)
}

How It Works

A VHS .tape script is generated from the session events
The tape uses the Catppuccin Mocha theme at 1400x800 resolution
Only tool_use events are rendered:
- Bash: Shows the command being typed, abbreviated output, and a status indicator
- Read/Edit/Write: Shows a comment line with the file path
- Task: Shows an "Agent:" comment with the task description
Each event includes a brief pause for readability
VHS renders the tape to the specified MP4 path

Tape Configuration

The generated tape uses these defaults:

FontSize 16
Width 1400
Height 800
TypingSpeed 30ms
Theme "Catppuccin Mocha"
Shell bash