I’m building this day by day, but you can begin with my new blog post on the topic, which has some great resources!
Synopsis: Although you can go to many individual agents’ websites to see their submission guidelines and sample query letters, it’s harder to find good synopsis advice or samples. That’s partly because the expectation is changing, and agents often lately want a 1-2 page version when not that long ago, the norm was much longer. I will keep updating this as I learn more about this process.
Reedsy (always a good resource despite steering you towards editorial service purchases)
An agent’s blog on synopses (very topical, but includes some other links)