krometrail-chrome

Krometrail — Browser Recording & Control (CLI)

Use the krometrail chrome commands to record browser sessions, drive Chrome with batch actions, and investigate what happened.

When to use

• The user reproduced a bug in the browser and dropped markers — investigate the session
• A web app has network errors, console errors, or unexpected behavior — search and inspect the recording
• You need to drive the browser (navigate, click, fill forms, wait) as part of a reproduction
• You need to compare browser state before and after an action — diff between markers

Recording

# Launch Chrome and record at a URL (isolated profile avoids conflicts)
krometrail chrome start --url http://localhost:3000 --profile krometrail

# With framework state capture (React, Vue)
krometrail chrome start --url http://localhost:3000 --framework-state auto

# Attach to an already-running Chrome (must have --remote-debugging-port=9222)
krometrail chrome start --attach

# Place markers at key moments
krometrail chrome mark "submitted form"
krometrail chrome mark "error appeared"

# Check status
krometrail chrome status

# Reload page and clear buffer (clean slate without restarting)
krometrail chrome refresh

# Stop recording
krometrail chrome stop
krometrail chrome stop --close-browser

Batch browser actions

Drive the browser with a sequence of steps in one call. Requires an active recording (start first).

# From a JSON file
krometrail chrome run-steps --file steps.json

# Inline JSON
krometrail chrome run-steps --steps '[{"action":"navigate","url":"/login"},{"action":"fill","selector":"#email","value":"[email protected]"},{"action":"click","selector":"#submit"}]'

# Save a named scenario for later replay
krometrail chrome run-steps --file steps.json --name login-flow --save

# Replay a saved scenario (no steps needed)
krometrail chrome run-steps --name login-flow

# Screenshot only on errors
krometrail chrome run-steps --file steps.json --screenshot on_error

# Disable auto-markers
krometrail chrome run-steps --file steps.json --no-markers

Each step is auto-marked (step:1:navigate:/login, step:2:fill:#email, etc.) and auto-screenshotted for investigation.

Steps JSON format

[
  { "action": "navigate", "url": "/login" },
  { "action": "fill", "selector": "#email", "value": "[email protected]" },
  { "action": "fill", "selector": "#password", "value": "secret" },
  { "action": "submit", "selector": "#login-form" },
  { "action": "wait_for", "selector": ".dashboard", "timeout": 5000 },
  { "action": "screenshot", "label": "after-login" }
]

Available actions: navigate, reload, click, fill, select, submit, type, press_key, hover, scroll_to, scroll_by, wait, wait_for, wait_for_navigation, wait_for_network_idle, screenshot, mark, evaluate

Key tips:

• Use reload (not navigate to the same URL) for a full page refresh — navigate may hit SPA client-side routing cache
• Use press_key with key: "Enter" to submit forms that lack a <button type="submit"> — this is common in chat UIs, search bars, and custom form components
• Start with a screenshot step before interacting to understand the current page state

Investigating sessions

# List recorded sessions
krometrail chrome sessions
krometrail chrome sessions --has-errors

# Overview of a session
krometrail chrome overview <session-id>
krometrail chrome overview <session-id> --around-marker <marker-id>

# Search events
krometrail chrome search <session-id> --query "payment failed"
krometrail chrome search <session-id> --status-codes 500
krometrail chrome search <session-id> --framework react --pattern stale_closure

# Inspect a specific event
krometrail chrome inspect <session-id> --event <event-id>
krometrail chrome inspect <session-id> --marker <marker-id>

# Compare two moments
krometrail chrome diff <session-id> --from <moment> --to <moment>

# Generate reproduction steps or test scaffolds
krometrail chrome replay-context <session-id> --format reproduction_steps
krometrail chrome replay-context <session-id> --format test_scaffold --framework playwright

# Export as HAR
krometrail chrome export <session-id> --format har --output session.har

See references/chrome.md for the full reference.

What gets captured

• Network: All XHR/fetch requests with headers, bodies, status codes, timing, WebSocket frames
• Console: All console output with levels, arguments, and stack traces
• DOM mutations: Structural changes — forms, dialogs, sections
• User input: Clicks, form submissions, field changes
• Screenshots: At markers, on errors, and during step execution
• Storage: localStorage/sessionStorage mutations
• Framework state (if enabled): React/Vue component lifecycles, state diffs, bug patterns

Investigation strategy

1. Start with the overview. Shows event counts, markers, and errors at a glance.
2. Narrow with search. Find specific errors, status codes, or framework patterns.
3. Deep-dive with inspect. Full event detail — request/response bodies, surrounding events, screenshots.
4. Compare with diff. What changed between two moments — new errors, state mutations, network failures.
5. Generate reproduction. Test scaffolds or step-by-step reproduction instructions.

Chrome launch failures

If chrome_start fails with "Chrome exited immediately":

1. Ask the user to close their Chrome browser, then retry
2. If they can't close Chrome, ask them to run: google-chrome --remote-debugging-port=9222 --user-data-dir=/tmp/krometrail-chrome <url> Then use: krometrail chrome start --attach
3. Do NOT use pkill -f chrome — this kills Electron apps (Discord, VS Code, Unity Hub, etc.)

Tips

• Markers are your anchors — search and diff around them
• Step markers (step:N:action:detail) appear automatically during run-steps execution
• Use --around-marker in overview to focus on a specific moment
• Framework patterns (stale closures, infinite re-renders, missing cleanup) are auto-detected when --framework-state is enabled
• Screenshots are captured automatically at markers, on errors, and during step execution
• 200 response but empty/broken page? The response body may contain streaming errors or unexpected content. Use inspect --event <id> --include network_body to see the actual response. Also check server logs (Docker, process output) — the error may be server-side
• Screenshot shows the same broken state after retry? Use reload (not navigate) to force a full refresh. SPAs may restore cached client-side state on navigate