hubcap trace - Capture a Chrome performance trace

When to use

Capture a Chrome performance trace for CPU profiling and runtime analysis. Open the output file in Chrome DevTools Performance panel to visualize flame charts, paint events, and layout shifts. Use metrics for a quick performance check without generating a full trace.

Usage

hubcap trace --output <file> [--duration <duration>]

Arguments

None.

Flags

Flag	Type	Default	Description
`--output`	string	`""`	Output file path (required)
`--duration`	duration	`1s`	Trace duration

Output

Field	Type	Description
`file`	string	Path to the written trace file
`size`	int	File size in bytes

{"file":"trace.json","size":54321}

Errors

Condition	Exit code	Stderr
Missing —output flag	1	`usage: hubcap trace --duration <d> --output <file>`
Chrome not connected	2	`error: connecting to Chrome: ...`
Cannot write to file	1	`error: writing file: ...`
Timeout	3	`error: timeout`

Examples

Capture a 1-second trace (default duration):

hubcap trace --output trace.json

Capture a 5-second trace:

hubcap trace --output trace.json --duration 5s

Navigate to a page and trace its load performance:

hubcap goto "https://example.com" && hubcap trace --output load-trace.json --duration 3s

Capture a trace with a timestamped filename and report the size:

hubcap trace --output "trace-$(date +%s).json" --duration 2s | jq '"Trace size: \(.size) bytes"'