Read your AI agent's session logs the way they were meant to be read.

A VS Code extension that turns raw .jsonl agent transcripts into a clean, inspectable, searchable conversation — with first-class support for sub-agent linking and side-by-side multi-session comparison on a shared timeline.

Install · Features · Getting started · Configuration · FAQ

Why?

If you've ever opened an AI agent's chat-history .jsonl file in a plain editor, you've seen this:

{"id":"chatcmpl-abc","parentId":"...","timestamp":1782133268740,"type":"function_call",
"providerData":{"messageId":"…","model":"…","argumentsDisplayText":"subagent_type: …"},
"callId":"tooluse_x9fHWvn496nS0JPI4QYdiB","name":"Read","arguments":"{\"file_path\": …}",
"sessionId":"…","cwd":"…"}

…one giant unreadable line per message, sub-agent calls scattered across sibling files, no way to tell which assistant turn produced which tool call.

Chat History Viewer parses these files, normalizes them into a uniform conversation model, and renders them as messages — with markdown, tool arguments, sub-agent links, and a timeline view for multi-session debugging.

Features

🧵 Single-session view

Per-message inspection: type · timestamp · id · role · tool name · tool arguments — all visible at a glance, click an id to copy.
Markdown rendering for assistant text and tool results, with auto-collapse of long blocks and an inline expand/collapse toggle.
Bulk selection & hide: tick messages, hide them to declutter, then Show hidden / Restore all to bring them back.
Type filter chips (USER, ASSISTANT, TOOL CALL, TOOL RESULT, SNAPSHOT, OTHER) and a free-text search across id / text / tool name / arguments.
Search with context: when you find a match, ±N surrounding messages are kept visible so you can read the up- and down-stream conversation without losing the filter. Adjustable from "match only" up to "all".
Raw JSON drawer on every message for when you really need to dig in.
Full IME support — Chinese / Japanese / Korean input works correctly in the filter box.

🔗 Sub-agent linking

When an Agent tool invokes a sub-agent, the viewer detects the link via three independent channels and resolves the sub-agent's .jsonl file. Click ▶ Open sub-agent on the tool call and the sub-session opens as a new tab, with breadcrumbs back to the parent.

📊 Side-by-side compare mode

Open N sessions as columns sharing a single time axis. Messages from every session interleave in real chronological order, with idle gaps collapsed into compact ↕ gap 12m separators so you can see who was doing what while another session waited.

   time      col1: main        col2: planner    col3: vision-reader
   10:01:23  user: 帮我...
   10:01:25  assistant: ok…
   10:01:30  ▶ Agent ─────────▶  …                ·
   10:01:42                       user: …            ·
   10:01:55                       assistant: …       ·
   ↕ gap 4m
   10:05:31  tool_result        ·                 user: 截图描述
   10:05:48  assistant: …       ·                 assistant: …

Two entry points:

Command palette → Chat History: Compare Multiple Sessions…
Explorer: select several .jsonl files, right-click → Chat History: Compare as Side-by-Side

Once you're in compare mode, clicking a ▶ Open sub-agent link appends the sub-agent as a new column to the right so you can watch parent and child agents collaborate on the same timeline.

� Supported formats

Out of the box this extension parses CodeBuddy / Claude-Code style JSONL transcripts. Support for additional formats (Cursor sessions, OpenAI Assistants logs, …) is on the roadmap.

Install

From a .vsix (recommended for now):

code --install-extension chat-history-viewer-<version>.vsix

Or, search "Chat History Viewer" in the VS Code Extensions view (publisher: devoszhang).

Getting started

Open a single session

Three ways, pick whichever is closest to where you are:

Where you are	How to open
`.jsonl` file in the Explorer	Right-click → Chat History: Open Current File
`.jsonl` file already open in the editor	Editor title bar → same command, or the Reopen Editor With… menu and pick Chat History Viewer
Nowhere in particular	`⌘⇧P` / `Ctrl+Shift+P` → Chat History: Open JSONL…

Compare multiple sessions

Command palette: Chat History: Compare Multiple Sessions…, then multi-select the files in the dialog.
Or, multi-select .jsonl files in the Explorer (Ctrl/Cmd + click), right-click, Chat History: Compare as Side-by-Side.

File layout convention

The default parser locates sub-agent transcripts by probing several common on-disk layouts, in this order, until one matches:

<dir>/<session>.jsonl                              # parent
<dir>/<session>/subagents/agent-XXXX.jsonl         # canonical
<dir>/<session>/agent-XXXX.jsonl                   # flattened (newer)
<dir>/subagents/agent-XXXX.jsonl                   # shared sibling dir
<dir>/agent-XXXX.jsonl                             # flat sibling

Sub-agent references are detected via three independent channels (most specific wins):

providerData.toolResult.subAgent.sessionId on a function_call_result
Trailing [Agent ID: agent-xxxx] text inside the tool output
Agent tool calls with arguments.subagent_type (provides the label; id is resolved from the matching result)

Configuration

Setting	Default	Description
`chatHistoryViewer.markdownCollapseThresholdLines`	`12`	Collapse a rendered message when it exceeds this many lines.
`chatHistoryViewer.markdownCollapseThresholdChars`	`600`	Collapse a message when its raw text exceeds this many characters.

FAQ

Q. My .jsonl file is huge (10MB+). Will this hang VS Code? No — the parser is streaming-friendly and the webview keeps the original records in memory but only renders visible messages. Files in the 100k-line range render in well under a second.

Q. Can I edit messages in this view? No, this is a read-only viewer. The original .jsonl is never written to. Use open source in the toolbar to jump to the raw file if you need to edit.

Q. The Chinese / Japanese / Korean filename in the tab is showing %E9%9C%80...? Fixed in 0.1.0 — file basenames are URL-decoded before being displayed.

Q. Does compare mode work with sub-agents? Yes, and it's where compare mode shines. Open a parent session, switch to compare view via the tab bar's ⇆ button, then click any ▶ Open sub-agent to append it as a new column.

Roadmap

Proportional timeline mode (row height ∝ real time elapsed)
Column-width drag handles in compare mode
Export filtered conversation to Markdown
Built-in parsers for Cursor and OpenAI Assistants logs

License

Released under the MIT License. See the LICENSE file shipped with the extension for the full text.

Chat History Viewer