Generating Data:

$et = new \EventTracer("myeventlog.json");

$et->begin("Eating Cake");
[...]
$et->end();

If filename isn't specified, then data will be buffered in-memory ($et->buffer) and can be written to disk in one go with $et->flush($filename).

Viewing Data:

Use Perfetto and "Open trace file"

Format Spec:

Google Doc

Uses the JSON Array Format because that's the one which can be appended to from multiple threads